基于粒子群算法的装配公差优化分配

装配公差分配是产品公差设计的重要组成部分.目前装配公差优化分配主要使用遗传算法.为了提高收敛速度,避免早熟收敛,提出了基于粒子群算法的装配公差优化分配方法.采用了基于实数的编码表示方法,以装配公差分配的优化目标函数作为评价函数,利用罚常数将约束条件并入评价函数中.一个实例的优化结果表明所提方法的收敛性、稳定性和算法效率均优于基于遗传算法的方法.     

Sub-micron position measurement and control on precision machine tools with laser interferometry

The trend towards tighter part tolerances from precision machine tools is placing increased demands on position transducers on these machines. Improved accuracy, repeatability and resolution from the position transducers is required to match this trend.This paper describes a new performance modelling technique for laser interferometer systems. Each error affecting the measurement accuracy and repeatability is described in detail, along with the method to determine these performance measures. Two products from Hewlett-Packard — wavelength tracking compensation and the high resolution interferometer — are also described that will help meet the future measurement requirements for precision machine tools.     

Verifying the geometric precision of machine tools

A method is proposed for determining the basic tests of the geometric precision of a metal-cutting machine so as to assess the influence of its error on the precision of the manufactured parts.     

尺寸公差与形位公差混合优化分配

为解决尺寸公差与形位公差混合优化分配问题,提出了一种公差优化分配方法.根据成本-公差函数和尺寸公差与形位公差的关系,建立了以最小制造总成本为目标的非线性公差混合优化分配模型.该模型的约束包括装配尺寸链的功能要求和加工能力.求解该模型能同时得到优化的尺寸公差和形位公差.最后,分别用公差混合优化分配法和传统方法对一个实例进行公差分配,结果表明所提方法比传统方法更优越.     

面向数控机床维修维护服务的任务分配模型

针对数控机床维修维护服务任务分配过程中需在保证服务技术质量的前提下进行多目标决策的问题,构建了一种面向数控机床维修维护服务的任务分配模型。首先解析了数控机床维修维护任务分配时所需的故障特征知识和人员特性,并对各特性知识进行了形式化说明,采用加权欧氏距离的方法计算维修维护质量需求与人员特性的匹配度;其次根据匹配度值剔除了不合理匹配的方案,并结合其它决策目标采用层次分析法(AHP)对保留方案进行了评估,最后通过实例进行验证。     

机床的光栅测量和数控系统的发展趋势

机床用光栅测量元件和数控系统是数控机床的两大核心部件,清楚地了解他们的发展趋势,对机床制造商和最终用户都有非常重要的意义。本文结合海德汉(H EID EN H A IN)公司的研究,阐述了现代数控机床用测量系统和数控系统的发展趋势,并着重介绍了机床的精度以及测量系统和数控系统     

一种混联精密装校平台的设计与分析

在分析LRU模块装校要求的基础上,提出了一种可实现6自由度调整的精密装校平台,研究了该平台调平机构和对接机构的自由度和运动类型,应用矢量法推导了各机构位置的正逆解,并将该解算式作为精密装校平台运动控制的核心算法,实现了样机的调平和对接两大主要功能,利用该功能实施了对LRU模块的自动化装校,证明了该精密装校平台可实现设计要求.     

Optimising tolerance allocation for mechanical components correlated by selective assembly

Selective assembly can enlarge the tolerances of mechanical components for easier manufacturing. However, the non-independent dimensions of correlated components make it difficult to optimise tolerance allocation for an assembly. This paper proposes a solution for this constrained optimisation problem consisting of tolerances and non-independent dimensions as design variables. The approach is to develop a simplified algorithm applying a Lagrange multiplier method to evaluate the optimal tolerances efficiently. The solution is shown to be a global optimum at the given correlation coefficients. The correlation coefficients are key elements in determining the optimal solution, which is demonstrated in the given examples. The results are helpful in designing tolerances for selective assembly.Notation A _j coefficient matrix off _j - B _i coefficient of cost function - C total manufacturing cost function - C _i manufacturing cost function forx _i - F _j thejth dimensional constraint function - f _j thejth quadratic constraint function - f quadratic constraint vector - H _j thejth Hessian matrix - J _kj element ofn×m Jacobian matrix - L Lagrangian - m number of assembly dimensions - n number of component dimensions - p number of equality dimensional constraints - T tolerance vector of component dimensions [mm] or [°] - tolerance ofx _i [mm] or [°] - tolerance ofZ _j [mm] or [°] - x component dimension vector - x midpoint vector - x _i component dimension [mm] or [°] - x _i midpoint ofx _i [mm] or [°] - Z _j assembly dimension [mm] or [°] - _j confidence coefficient forZ _j - _i confidence coefficient forx _i> - _j given design value ofZ _j [mm] or [°] - Lagrange multiplier vector - _j thejth Lagrange multiplier - * Lagrange multiplier vector at the optimum solution - correlation coefficient forx _i andx _k - _x standard deviation vector - _x ^* standard deviation vector at the optimum solution - _x ⁰ candidate point satisfying the constraintsf( _x ^* )=0 - standard deviation ofx _i      

Improving the dimensional precision of numerically controlled machine tools

In an era of rapid technological advances, manufacturing products must meet strict quality standards. In particular, metal-cutting equipment must ensure the required dimensional precision throughout its working life, with the minimum production costs. An appropriate mathematical apparatus is required to determine the errors in the system on the basis of preliminary and ongoing diagnostics.     

Characteristics of and measurement methods for geometric errors in CNC machine tools

The characteristics of geometric errors in CNC machine tools have been investigated in detail. These characteristics include position dependence, relativity, synthesis, and continuity. Tests have been designed to verify these properties, which can be used to guide the error measurement procedure. A new measurement procedure, called the relay method, has been developed. This method has high resolution and can be applied to measure geometric errors in the whole workspace. A machine has been calibrated by the relay method, and the results of error compensation show that the machine tool accuracy has been improved.     

Optimal tolerance design for mechanical assembly considering thermal impact

In this paper, a cost–tolerance model based on neural network methods is proposed in order to provide product designers and process planners with an accurate basis for estimating the manufacturing cost. Tolerance allocation among the assembly components is carried out to ensure that the functionality and design quality are satisfied considering the effect of dimensional and geometric tolerance of various components of the assembly by developing a parametric computer aided design (CAD) model. In addition, deformations of various components of mechanical assembly due to inertia and temperature effects are determined and the same is integrated with tolerance design. The benefits of integrating the results of finite element simulation in the early stages of tolerance design are discussed. The proposed method is explained with an application example of motor assembly, where variations due to both dimensional and geometric tolerances are studied. The results show that the proposed methods are much effective, cost, and time saving than the ones considered in literature.     

Coupling evaluation for material removal and thermal control on precision milling machine tools

Machine tools are one of the most representative machining systems in manufacturing. The energy consumption of machine tools has been a research hotspot and frontier for green low-carbon manufacturing. However, previous research merely regarded the material removal (MR) energy as useful energy consumption and ignored the useful energy consumed by thermal control (TC) for maintaining internal thermal stability and machining accuracy. In pursuit of energy-efficient, high-precision machining, more attention should be paid to the energy consumption of TC and the coupling relationship between MR and TC. Hence, the cutting energy efficiency model considering the coupling relationship is established based on the law of conservation of energy. An index of energy consumption ratio of TC is proposed to characterize its effect on total energy usage. Furthermore, the heat characteristics are analyzed, which can be adopted to represent machining accuracy. Experimental study indicates that TC is the main energy-consuming process of the precision milling machine tool, which overwhelms the energy consumption of MR. The forced cooling mode of TC results in a 7% reduction in cutting energy efficiency. Regression analysis shows that heat dissipation positively contributes 54.1% to machining accuracy, whereas heat generation negatively contributes 45.9%. This paper reveals the coupling effect of MR and TC on energy efficiency and machining accuracy. It can provide a foundation for energy-efficient, high-precision machining of machine tools.     

Research on surface normal measurement and adjustment in aircraft assembly

Drilling and riveting are commonly used in aircraft panel assembly process. Due to the fixture positioning error and the deformation of workpiece, the real position and orientation of the workpiece as well as its 3D geometry at the drilling position varies from the nominal CAD model, which would cause an unfavorable impact on assembly quality. Therefore, surface normal measurement and adjustment at the drilling position is of great importance. In this paper, a fast and effective non-contact measurement method for normal vector and height of moderately curved surfaces is accomplished by four laser displacement sensors, and a dedicated NC machine tool is also developed for normal adjustment. Firstly, a novel sensor calibration method based on laser tracker is introduced, which can acquire the sensors’ position and orientation in Tool Coordinate System (TCS) at the same time. The normal vector at hole position is calculated by cross product of any two non-parallel vectors constructed by the four laser projection points on the panel surface. Secondly, the kinematic model of the machine tool is established to calculate the adjustment of each axis of the machine tool with the Homogeneous Transformation Matrix (HTM). Besides, an innovative method to identify the distance of two rotary centers based on two laser interferometers is proposed. Finally, a series of experiments are conducted to validate the feasibility of the proposed method. The results show that the angle deviation can be reduced to less than 0.5° after adjustment, while the accuracy of the surface height is ±0.04 mm.     

精密机床主轴轴承振动的测量

着重介绍了在BVT-6仪器上测量精密机床主轴轴承振动的方法。通过对测量心轴结构的改进,保证了精密机床主轴轴承振动的测量,为该轴承的质量评价提供了可靠依据。     

基于任务的数控机床模糊可靠性分配方法

在分析现有数控机床可靠性分配技术局限的基础上,针对数控机床加工零件过程的动态性特征,将多阶段任务系统理论和任务可靠性原理结合起来,提出一种基于任务的可靠性分配方法。根据数控机床加工零件总任务的实际情况,建立数控机床的任务剖面层次模型。通过对数控机床元任务层的分析与研究,确定了运行时间、重要程度、复杂程度、技术水平和工作状况5个影响可靠性分配的重要因素。运用模糊集理论,充分考虑到多领域专家的意见和数控机床研发过程的风险性,定义了一种判定模糊真值的函数,给出一种确定隶属度的方法,并建立起数控机床可靠性分配指标体系和权重,以及元任务的模糊评判矩阵。以一个数控机床主加工元任务组为例,证明了该方法的可用性。     

数控机床误差检测技术新进展

介绍了现有的各种典型的检测方法和技术特点,重点介绍了国内外近二十年、特别是最近十年来数控机床误差检测领域的研究新进展,具体包括DBB法、激光干涉仪法应用研究的最新成果以及平面光栅和R-test等新型检测仪器和方法;分析了当前数控机床误差检测研究中存在的问题,并对今后的研究趋势做了进一步展望。