基于Ontology的装配公差规范的自动生成

针对几何产品公差规范设计中存在的不确定性问题,文章将本体理论引入到装配公差规范的设计中,为装配公差规范的自动化、智能化设计提供一种可行的方法。首先构建装配公差规范层次化表示模型,并采用OWL DL断言表示模型层次间的约束关系;其次,根据装配公差规范中的概念和关系,构建装配公差规范的本体模型;再次,根据装配公差规范设计领域的专家知识,使用语义网规则语言(SWRL)构建装配公差规范设计的推理规则;然后,根据构建的本体表示模型及定义的推理规则,构建装配公差规范设计知识库,在此基础上编写装配公差规范智能化设计算法;最后,以齿轮减速器为实例说明了装配公差规范自动生成的过程,并分析验证了该方法的有效性。     

Quantitative circularity tolerance analysis and design for 2D precision assemblies

Circular, cylindrical, or spherical features are fundamental geometric features in engineering. As precision requirement becomes more stringent, it is not sufficient to consider only size tolerance of circular and cylindrical parts. However, currently there is no quantitative and systematic way of assigning circularity and cylindricity tolerances. This paper investigates how to specify circularity tolerance quantitatively for 2D assemblies. Statistical matrices to quantify positioning error of two perfectly circular mating parts subject to size tolerance for both clearance and transition fit conditions are first developed. The analysis is then extended to nonideal profiles whose profile errors are assumed to deviate from a best-fit circle according to a normal distribution. The assumption of the normal distribution is then removed for more general results via computer simulation. For this purpose, an experimentally verified profile model is used to generate realistic profiles as those produced by various machining processes. Numerous pairs of these realistic profiles are then assembled virtually using Monte Carlo simulation to quantify their positioning errors. The simulation results and the analytical results are compared for cross-checking. Finally, systematic design procedures are proposed to assign circularity tolerance by prescribing a fit condition with a desirable process capability. By the nature of circularity tolerance, this paper addresses a 2D assembly. The result of this 2D analysis can be a foundation for more complicated 3D problems, such as assigning cylindricity tolerance.     

Geometric analysis of investment casting turbine blades based on digital measurement data简

A turbine blade is one of the key components of the aero-engine.Its geometric shape should be inspected carefully in the production stage to ensure that it meets the tolerance specification.In the present paper,an approach for investment turbine blade geometric shape analysis based on multi-source digital measurement is presented.Its key technologies,such as measurement data collection,blade model reliable alignment,geometric shape deviation fast calculation and visualization,were investigated.Actual measurement data from a structure light measurement device and a Coordinate Measuring Machine （CMM） for turbine blades were used to validate the presented method.The experimental results show that the proposed method is accurate,quick and effective to implement.     

机械零件几何知识及工艺知识计量理论和方法的研究

根据空间因素理论、零件表达的特征和计量的要求,定义了零件的表达空间,提出了一种新的零件表达模型。并从信息和描述复杂性两个方面对零件几何知识和工艺知识的计量理论与方法进行了研究,提出了运用最低加工机床的调整信息量作为零件尺寸及其公差知识量的计量方法。     

An expert system for generation of machine inputs for laser-based multi-directional metal deposition

Laser-based multi-directional metal deposition (LBMDMD) is a very effective way of fabricating a part directly from its digital model. The method, however, requires a lot of human intervention during the process planning. Driven by already developed expert systems for the process planning in Computer Aided Design (CAD) and manufacturing, this paper intends to suggest a task framework for the automation of the process planning for LBMDMD using principles of Artificial Intelligence (AI). The process can be divided into distinct steps, and geometric reasoning can be applied to determine a set of facts and rules for the automation. The principles of first order logic are applied for the representation and further simplification of the process into a set of “if–then” based rules. This paper explains the framework, the facts, and the rule base used for the process planning.     

A strategy for identifying static deviations in universal spindle head type multi-axis machining centers

This research was conducted in order to investigate the effectiveness of the checking method specified in ISO 10791-6 and to propose an additional method for identifying the geometric deviations inherent to five-axis machining centers with a universal spindle head. The specified method is not sufficient for assessing the influence of individual geometric deviations. Therefore, additional measurements are needed in order to use this checking method effectively. The spherical motion in the additional measurements is a modified version of the ISO standard. Some of the deviations are presumed based on the result of the additional measurements, and so the method of identifying the remainder of the geometric deviations was designed by analyzing the link geometry of the machine. The identification procedure consists of three steps. In the first and second steps, after performing two measurements, six out of ten deviations are identified by means of an observation equation. In the third step, four of the ten deviations are identified by means of the link geometry. The exactness of the proposed procedure for identifying the deviations inherent to the five-axis machine is confirmed through simulations.     

Early cost estimation for tolerance verification

This paper presents a methodology for estimating the verification cost of geometric tolerances at the design stage, which is useful for optimizing the tolerance specifications of mechanical products. The tolerance verification cost may be seen as the sum of the measurement and uncertainty costs. The measurement cost depends on the adopted device and on the measurement time. The uncertainty cost is related to type A (declaring a conforming part non-conforming) and type B (declaring a non-conforming part conforming) errors: these errors are strongly influenced by the measurement procedure, which depends on the measurement device and determines the measurement time. The methodology is illustrated and validated using simulation and industrial case studies.     

Swept volume generation for the simulation of machining processes

To enhance the accuracy of five-axis milling processes, a simulation based NC-path optimization provides an efficient approach. The key to a reliable simulation of cutting processes is the accurate geometric modeling of engagement conditions and the resulting workpiece geometry. The article proposes a novel approach to calculate the cutter profile for modeling swept volume with respect to trajectory of the cutter. In terms of envelope theory, a swept volume is created as a NURBS surface representation. The proposed method is robust and the results can be applied to material removal simulations based on Boolean operation, as well as discrete methods.     

Real-time NURBS command generators for CNC servo controllers

This study proposes a real-time Non-Uniform Rational B-Spline (NURBS) motion command generator for computer numerical control (CNC) machines to achieve the goal of high-speed and highly accurate machining. Different numerical algorithms for implementing the NURBS motion command generator are compared on the basis of both the computation time and the precision of geometric representation. In addition, to reduce the computation time such that the corresponding servo control laws can be executed in real time, both the NURBS motion command generator and the servo control laws are realized using a digital signal processor. Experimental results indicate that the proposed real-time NURBS command generator is able to provide a satisfactory performance.     

面向加工程序优化的铣削过程模拟技术

针对CAD/CAM系统不能自动生成加工参数的问题,国内外许多学者提出了利用加工过程模拟技术加工程序的思想,随着对切削机理认识的不断加深和计算机仿真技术的发展,铣削加工模拟优化系统得到了大量的研究和开发。对铣削过程模拟中的两个关键技术-几何模拟技术和物理模拟技术进行了归纳和分析。     

数字式电／气控制元件计算机辅助测试系统的研究

本文对数字式电／气控制元件CAT系统进行了初步研究，并着重介绍了数字式电／气控制元件试验装置、CAT系统的硬件组成及软件模块结构。     

Computer-aided operational dimensioning for process planning

One of the important steps of process planning is to determine the tolerance and mean size for each working dimension. This paper presents a computer-aided operational diminsioning systems which can determine tolerances systematically and calculate mean sizes of working dimensions automatically for a process plan. The system is based on the tolerance charting technique. Firstly, a tree theoretic representation for a tolerance chart is described in this paper. Three trees can be generated from blue print dimensions, stock removals and working dimensions of a tolerance chart. The algorithms for generating the trees are provided, and these trees can be used to identify dimensional chains and solid stock removals in a tolerance chart. Then a linear programming model is built to determine the tolerance of each working dimension. Finally, a mathematical model of linear equations for calculating mean working dimensions is formulated from the dimensional chains.     

A non-rigid registration method for the efficient analysis of shape deviations in production engineering applications

A common requirement in production engineering applications is the comparison of designed and as-built parts. Due to manufacturing influences and geometric changes incorporated during physical prototyping, there may exist significant deviations between these shapes. In order to compensate the manufacturing influences and to incorporate geometric changes into the virtual design, a detailed analysis of the deviations is required. The designed (or reference) shape is usually given in terms of a CAD data set, while the as-built (or test) geometry is acquired by digitization of the physically manufactured prototype. Given these two geometries, one is faced with the problem of determining points of correspondence between them. This is also referred to as registration. In rigid registration, correspondences are determined by first aligning the two geometries rigidly using a best-fit approach. Subsequently, the correspondences between the aligned geometries are determined by finding for a point of one shape the closest surface point on the other. While several efficient rigid registration methods exist, they do not account for shape deviations, resulting in inaccurate correspondences when applied to such geometries. Non-rigid registration methods, conversely, do not search for a global best-fit alignment, but instead affect a deformation of the one geometry onto the other, allowing for an improved correspondence calculation. Most published state-of-the-art non-rigid registration methods are not necessarily applicable to production engineering scenarios due to, among others, the typical data sizes and the required level of accuracy in the correspondence determination. A further hindrance is their lack of shop-floor applicability, attributable to their calculation times as well as to the expertise that their application requires on behalf of the user. This paper presents a non-rigid registration method for the efficient calculation of correspondences in production engineering scenarios. By combination of several established methods from the field of geometric modeling, the test shape is iteratively deformed onto the reference shape. When the deformed test shape satisfiably approximates the reference geometry, correspondences are determined by projection. The procedure is applied to the problem of springback behavior, which arises in sheet metal forming. A validation of the method is achieved by comparing the calculated correspondences with the ideal correspondences, as determined by finite element simulation.     

Prediction of the dynamic behaviour of machine tools during the design process using mechatronic simulation models based on finite element analysis

Increased productivity, higher velocities and acceleration for feed and cutting motions are requirements for innovative machine tools. At the same time the production process must achieve reduced form and position deviations of the work-piece. Therefore knowledge of the dynamic behaviour of machine tools during the design process is essential to develop high-performance machines. Using finite element analysis and mechatronic simulation, taking the mechanical, electrical and control systems into account, is the first step for optimisation. Developing the control parameters using these simulation techniques is one of the major steps in detecting the mechatronic characteristics. This paper presents a method for developing the control parameters concerning tool to work-piece deviations of mechatronic simulation models including disturbance variables. As an example a 2-axis CNC test stand for feed drive axes will be visualised with its simulation and measurement results in the time and the frequency domain.     

数控系统圆形工件智能测心定位研究

为解决数控机床钢环套装圆形工件定位精度问题,对圆形工件测量定位进行研究,从而保证套装精度.采用计算机仿真软件分析并确定圆形工件内部有效测量点分布位置,建立几何模型,选取测量方式.通过实验对仿真结果以及几何模型进行验证,利用数字测量探头配合数控系统计算工件圆心坐标.与理论圆心坐标相比,测量圆心坐标误差小于0.2 mm,满...     

Generative adversarial networks for tolerance analysis

Many activities in design and manufacturing rely on realistic product representations considering geometrical deviations to assess their effects on the product function and quality. Though several approaches for tolerance analysis have been developed, they imply several shortcomings, such as the lack of form deviations consideration and the high manual modelling effort. In this paper, a novel shape-agnostic approach supported by generative adversarial networks is developed for the automated generation of part representatives with geometrical deviations. A workflow for generating these variational part representatives is highlighted and tolerance analysis case studies demonstrate the effectiveness of the proposed approach.     

A new geometric error modeling approach for multi-axis system based on stream of variation theory

This paper introduces a new geometric error modeling approach for multi axes system (MAS) based on stream of variation (SOV) theory, especially for multi-axis precision stage. SOV is used for measuring product quality for some complicated multi operations system, which is widely used in error propagation in engineering field. This paper introduces SOV concept into geometric error modeling for MAS. Instead of different process in manufacture, the new error modeling approach regards each axis as a station in MAS, and calculates the deviations after each station which is considered as upstream factor to next station. It is clear to observe how geometric errors give influence and how deviations accumulate. Different with conventional methods which are only used for error compensation in machine tools, the new error model is beneficial for sensitive error control and optimal configuration selection in design part. In addition, the new error modeling has some merits such as debugging easily due to observe the deviations after every station. A case study of new error modeling procedure for six-axis stage (SAS) in optoelectronic packaging system (OPS) is developed, and applications related to error reduction order and optimal configuration selection are processed based on the new error model.     

The skin model,a comprehensive geometric model for engineering design

The modelling of product shapes and dimensions is now largely supported by geometric modelling tools. However, the underlying geometrical variations cannot be addressed efficiently when covering the overall product life cycle. The fundamental concept of skin model has been developed as an alternative to the nominal model and covers geometric deviations that are expected, predicted or already observed in real manufacturing processes.     

Enhancement of geometric accuracy of five-axis machining centers based on identification and compensation of geometric deviations

The present paper describes the enhancement of kinematic accuracy of five-axis machining centers with a tilting rotary table. Geometric deviations inherent to the five-axis machine are calibrated through the actual trajectories measured by two different settings of a ball bar in simultaneous three axis motion. Measurement using a cylindrical coordinate system is superior to measurement using a Cartesian coordinate system from the viewpoint of the number of measurements. In order to verify the effectiveness of the calibration method, the inherent geometric deviations measured on the cylindrical coordinate system were corrected through the post processing of NC data for cutting the cone-frustum.The relative displacement between the tool center point and the workpiece was detected by the ball bar. Based on the experimental results, it is confirmed that the radius, center position, and roundness of the three-dimensional circular trajectory are improved when the inherent geometric deviations are corrected.