A Knowledge-Navigation System for Dimensional Metrology

Geometric dimensioning and tolerancing (GD&T) is a method to specify the dimensions and form of a part so that it will meet its design intent. GD&T is difficult to master for two main reasons. First, it is based on complex 3D geometric entities and relationships. Second, the geometry is associated with a large, diverse knowledge base of dimensional metrology with many interconnections. This paper describes an approach to create a dimensional metrology knowledge base that is organized around a set of key concepts and to represent those concepts as virtual objects that can be navigated with interactive, computer visualization techniques to access the associated knowledge. The approach can enable several applications. First is the application to convey the definition and meaning of GD&T over a broad range of tolerance types. Second is the application to provide a visualization of dimensional metrology knowledge within a control hierarchy of the inspection process. Third is the application to show the coverage of interoperability standards to enable industry to make decisions on standards development and harmonization efforts. A prototype system has been implemented to demonstrate the principles involved in the approach.     

Tolerance transfer in sheet metal forming

A literature review of sheet metal forming errors as well as geometrical dimensions and tolerances (GD&T) shows that the theoretical means for the allocation of process tolerances with respect to GD&T are insufficient. In order to judge the influence of geometrical process errors (e.g., angular errors of bends), two typical sheet metal designs with parallelism and a position tolerance are studied. These case studies comprise a detailed analysis of tolerance chains including angular errors of bends and their positions. The resulting errors are compared with those resulting from length dimensional process errors and conclusions are drawn.     

Integrating GD&T into dimensional variation models for multistage machining processes

Recently, the modelling of variation propagation in multistage machining processes has drawn significant attention. In most of the recently developed variation propagation models, the dimensional variation is determined through kinematic analysis of the relationships among error sources and dimensional quality of the product, represented by homogeneous transformations of the actual location of a product's features from their nominal locations. In design and manufacturing, however, the dimensional quality is often evaluated using Geometric Dimensioning and Tolerancing (GD&T) standards. The method developed in this paper translates the GD&T characteristic of the features into a homogeneous transformation representation that can be integrated in existing variation propagation models for machining processes. A mathematical representation using homogeneous transformation matrices is developed for position, orientation and form characteristics as defined in ANSI Y14.5; further, a numerical case study is conducted to validate the developed methods.     

Graph-based set-up planning and tolerance decomposition for computer-aided fixture design

Set-up planning plays an important role in integrating design with process planning and fixture design. Its main task is to determine the number and sequence of set-ups, and select locating datum, machining features and operations in each setup. Computer-based set-up planning may be used to generate automatically a setup plan based on tolerance analysis for minimizing locating error, calculating machining error stack-up and improving CAD/CAPP/CAFD (Computer-aided Fixture Design) integration efficiency. Most of the current set-up planning systems were based on empirical methods (such as rule and knowledge base) and their applications background was plus/minus a dimensioning and tolerancing (GD&T) scheme. Today, more and more industries are using a true positioning Geometric Dimensioning and Tolerancing (GD&T) scheme in design and manufacturing. To support this requirement, this paper presents an analytical set-up planning approach with three techniques, (1) an extended graph to describe a Feature and Tolerance Relationship Graph (FTG) and a Datum and Machining Feature Relationship Graph (DMG), which could be transferred to an analytical computer model; (2) seven set-up planning principles to minimize machining error stack-up under a true positioning GD&T scheme; and (3) tolerance decomposition models to partition a tolerance into interoperable machining errors, which could be used for locating error analysis or for feedback to design stage for design improvement. These techniques are implemented in a computer system and it is integrated with a commercial CAD/CAM system to support an automobile manufacturing enterprise in fixture design and production planning.     

Tolerance analysis of a product coupling geometric and architectural specifications in a probabilistic approach

This article describes tolerance analysis using a reliability-based approach to ensuring that a functional condition is satisfied. A particular feature of this procedure is that it defines the combined effects of geometric and dimensional ISO specifications for product parts, and the architectural parameters that define the relative positions of parts in contact. In the first part, we describe configuring the product parameters by geometric deviations, and from this, a global model is produced to characterise the variation in rotor/stator clearance in a turboshaft engine turbine. This model relies on tolerance zone dimensions, dimensional tolerances and architectural parameters. When clearance is examined using the reliability-based approach, links emerge between the turbine’s architectural parameters and its geometric and dimensional specifications. Indicators can then be deduced which guide the designer in selecting the optimum turbine architectures.     

Automatic evaluation of form errors in high-density acquired surfaces

In this paper the authors present an original methodology aiming at the automation of the geometric inspection, starting from a high-density acquired surface. The concept of intrinsic nominal reference is herein introduced in order to evaluate geometric errors. Starting from these concepts, a new specification language, which is based on recognisable geometric entities, is defined. This work also proposes some surface differential properties, such as the intrinsic nominal references, from which new categories of form errors can be introduced. Well-defined rules are then necessary for the unambiguous identification of these intrinsic nominal references. These rules are an integral part of the tolerance specification. This new approach requires that a recognition process be performed on the acquired model so as to automatically identify the already-mentioned intrinsic nominal references. The assessable errors refer to recognisable geometric entities and their evaluation leaves the nominal reference specification aside since they can be intrinsically associated with a recognised geometric shape. Tolerance specification is defined based on the error categories which can be automatically evaluated and which are an integral part of the specification language.     

等值原则及其在圆度误差评定中的应用研究

 坐标测量机和计算机技术的发展, 在公差检测、描述以及数学定义等方面都提出了新的挑战。文章尝试性地提出了基于材料力学中固体连续性假设的等值原则, 阐述了按等值原则确定实际要素的理想形状要素, 在该理想形状要素的基础上, 进行相似胀缩来形成便于计算机描述的公差带, 通过坐标轴平移和旋转来完成公差带的精确数学描述, 从而实现尺寸公差、形状公差和位置公差等统一的思想。最后, 在圆度误差评定中进行了应用举例, 并得到了一些有价值的结论。     

Locating error analysis and tolerance assignment for computer-aided fixture design

Based on the considerations of locating the error source and true positioning geometric dimensioning and tolerancing (GD/T), this paper presents a locating error analysis approach for set-up planning and fixture design. It includes three techniques: (1) by synchronizing locating elements with locating features, a fixturing coordination system is defined to simulate the actual locating situation; (2) a vectorial tolerance zone definition is explored. Compared with the tolerance zone definition published in ISO and ANSI Y14.5 standards, the biggest difference is that this definition is built up on the fixturing coordination system. Consequently, it is especially suitable for locating error analysis; (3) a locating error evaluation algorithm is developed with sensitivity analysis functions. The proposed models and techniques have been implemented with commercial CAD systems and have been applied to automobile manufacturing companies.     

Hybrid neuro-fuzzy approach to the generation of measuring points for knowledge-based inspection planning

A knowledge-based inspection planning system is presented that can generate effective and consistent inspection plans automatically. The knowledge-based inspection planning system integrates part geometry information, tolerance information and heuristic knowledge of experienced inspection planners to determine the numbers and positions of measurement points. The system receives the tolerance information from users and stores it in the common database with 3D CAD geometry. A set of fuzzy rules and membership functions is automatically extracted from historic learning data using a hybrid neuro-fuzzy method. After the fuzzy rules are generated by the hybrid neuro-fuzzy model, a genetic algorithm is applied to optimize the weight parameters to find the best values for the constants. The proposed knowledge-based inspection planning system provides the stable and consistent inspection plan by removing the subjectivity of a human planner.     

Synthesis of a web-based dimensional verification system for styling processes

A design methodology is proposed for a web-based collaborative system applicable to styling processes in the distributed environment. By using the developed system, design reviewers of new products are able to confirm geometric shapes, inspect dimensional information of products through measured point data and exchange views with other design reviewers on the internet. Functional requirements for the design of this web-based dimensional verification system are suggested. ActiveX-server architecture and OpenGL plug-in methods using ActiveX controls realize the proposed system. Visualization and dimensional inspection of the measured point data are conducted directly on the web; conversion of point data into a CAD file or VRML form is not required in the styling process. Dimensional verification results and design modification ideas are uploaded through markups and/or XML files during the collaboration processes. The XML files, allowing information sharing on the web, are independent of the platform. It is possible to diversify the information sharing capability among design collaborators. The validity and effectiveness of the developed system are confirmed by case studies.     

Manufacturing signature and operating conditions in a variational model for tolerance analysis of rigid assemblies

The need of a univocal language for geometrical product specification considering all steps of the product life cycle such as design, manufacturing, and inspection is inevitable. Most models for Computer-Aided Tolerancing proposed by researchers and used in industry do not fully conform with standards. Moreover, most of them make severe assumptions on observable geometric deviations and can therefore hardly handle all kinds of 3D tolerances. These lacks inspired the idea and the development of a discrete geometry framework that is capable of considering geometric deviations of different stages of the product life cycle and is versatile regarding current and future tolerancing standards. This work uses a point cloud-based geometry representation scheme to implement the pattern left on the surfaces by a manufacturing process; then, this scheme has been inserted in a variational approach for tolerance analysis. Moreover, gravity and friction among the parts to assemble have been simulated too. In this way, a new Computer Aided Tolerancing (CAT) simulation tool has been developed; it approaches reality more than existing software packages do. To verify the effectiveness of the new CAT simulation tool, it has been applied to two case studies. The obtained results have been compared with those due to a geometrical model that has been developed by simulating what happens among the parts in the actual assembly. The obtained results show how the new CAT simulation tool gives results nearer to reality than literature models do.     

设计与制造中的统计几何公差建模及应用

几何与尺寸公差(形位公差GD&T)广泛用于机械工程设计与制造中重要几何特征的偏差控制.相对较成熟和简单的尺度公差建模与分析,几何公差统计建模与分析更具挑战性,是当前CAD技术中尚未但亟待解决的课题之一.现提出采用统计几何模态模型(SMA)方法解决这一问题.SMA可识别刻划与解释测量数据中的几何特征信号模式及其变化,从而服务于制造中的(公差)质量检验、诊断及变化模式的统计建模.在设计中SMA可进行模态重组综合,从而再现或仿真几何特征偏差的随机变化进行统计几何公差分析.     

Structured approach to the design of a production data analysis facility. Part 1: Conceptual design and information requirements

The paper reports research into a workshop-oriented machine and inspection framework for a contemporary metalworking small manufacturing enterprise (SME) that cannot be satisfactorily achieved by the rigid scaled-down versions of software applications employed within larger companies. It identifies a structured approach to the design and conceptualization of a production data analysis framework that is supported by the use of order and manufacturing data. A major feature of the framework is its generic applicability and totally integrated approach to provide rapid manufacturing control from intelligent feedback data from the inspection and manufacturing data analysis activities of manufactured components. This production data analysis approach is formally expressed through the combined application of both the activity analysis formalism of IDEF0 and object-oriented information analysis methodology of Booch. The systematic approach employed by the integrated production data analysis framework provides both product and manufacturing process control in order to close the manufacturing feedback loop. These integrated phases are described and involve the concurrent machine operation and inspection planning, simultaneous production code generation, comparative tolerance analysis, and manufacturing data analysis of manufactured components. The final part of the paper provides a critical discussion on a number of major issues of the approach and identifies the advantages and limitations of the research.     

Structured approach to the design of a production data analysis facility Part 2: Implementation and evaluation

This paper reports research into a novel machining, inspection and analysis facility directed towards a small manufacturing enterprise. A major feature of the facility is the ability to produce rapid manufacturing control through feedback data generated from the seamless integration of machining, inspection and production data analysis activities in order to influence the regeneration of NC part programs. The major contribution of the paper explores the implementation and evaluation of a prototype production data analysis facility that consists of four constituents: machine and inspection planning, production code generation, comparative tolerance analysis, and manufacturing data analysis, the execution of which is supported by the use of order and manufacturing information models. An integrated multifunctional prototype production data analysis software tool has been developed for a limited number of manufacturing features for 2½D prismatic components. This prototype software tool has been tested and is critically reviewed with future work.     

Reliability analysis of fault tolerant memory arrays

A model is developed to represent computer memory module reliability as a function of memory array reliability under a fault tolerant design. The fault tolerance feature of the array actually results from a revision in the use of the array so that with respect to some failure modes, the array becomes a K out of N rather than a series system. The model is used to determine array reliability under fault tolerance. The ratio of module reliability under fault tolerance to that without this feature is used as a measure of the benefits of revising array use. A key feature of the analysis is the fact that not all faults can be tolerated. The elemental memory devices examined conform to a decreasing Weibull hazard model. Consequently, evaluation of the general model for the K out of N system realized must be done numerically. However, for the special case in which K=N-1, a closed form expression for the performance measure is obtained. This special case occurs for the application of interest and it is shown that the performance measure always exceeds one and depends directly upon the proportion of faults that can be tolerated. Thus the value of fault tolerance is shown to depend upon the extent to which the array will tolerate faults. This provides a basis for deciding whether or not fault tolerance should be implemented.     

Concurrent process planning for finish milling and dimensional inspection of sculptured surfaces in die and mould manufacturing

With the introduction of computer-aided tools, traditional manufacturing tasks such as design, machining and inspection are now highly automated. However, due to the complexity and enormous knowledge involved in each process, most of these activities are still dealt with separately. Recent development of concurrent engineering emphasizes the importance of bringing manufacturing knowledge into the early design stage for optimum product and process design. In this paper, a knowledge-based CAD/CAM system which integrates process planning for finish milling and dimensional inspection of sculptured surfaces in die and mould manufacturing is presented. Optimum production plans are determined by minimizing the integral cost of machining and inspection. NC path generation and inspection planning are then verified by dynamic geometric simulations which provide the designer with the evaluations of machinability and inspectability. The implied significance is that strong inter-dependency may exist among various design life-cycle activities and that optimum solutions can be obtained by taking into account the interactions of the life-cycle events.     

The RGM data structure: a nominal interpretation of an acquired high point density model for automatic tolerance inspection

In a previous paper (Di Angelo, L., Di Stefano, P. and Morabito, A., 2011. Automatic evaluation of form errors in high-density acquired surfaces. International Journal of Production Research, 49 (7), 2061–2082) we proposed an original methodology for the automation of the geometric inspection, starting from an acquired high-density surface. That approach performed a recognition process on the acquired data aiming at the identification of some intrinsic nominal references. An intrinsic nominal reference was detected when a geometric property was recognised to be common to a set of adjacent points in the 3D data set representing the acquired object. The recognition of these properties was carried out based on some rules. Starting from these concepts, a new specification language was defined, which is based on recognisable geometric entities. This paper expands the category of intrinsic nominal references to include new mutual intrinsic orientation, location and dimensional properties pertaining to 3D features. This approach involves the automatic construction of a geometric reference model for a scanned workpiece, called recognised geometric model (RGM). The domain of the representable entities within the RGM strictly depends on the rules used for the recognition of the intrinsic properties. In particular, this paper focuses on the rules for the recognition of the orientation and location properties between non-ideal features. When using the RGM, tolerances are specified according to the set of available and recognisable intrinsic nominal references. Based on the geometric product specification, the RGM data structure can be queried to capture some quantitative information concerning special intrinsic geometric parameters and/or non-idealities.     

Estimation of measurement uncertainties using virtual fringe projection technique

One of the main tasks of the quality test is the inspection of all relevant geometric parts related to the predefined tolerance range, whereas the uncertainty of measurement has to be less than the tolerance range. The reachable uncertainty of measurement can be determined using method A of the ISO Guide to the Expression of Uncertainty in Measurement (GUM), which is expensive and time consuming and has to be carried out for each individual metrologic case. Furthermore, it is possible to check the suitability of the measurement system for the planned inspection using virtual measurement techniques and therewith to reduce the time and money spent. This means that the uncertainty of measurement is estimated using method B of the GUM. In this paper, a virtual fringe projection system is used for the estimation of the uncertainty of measurement, which is compared with the uncertainty of measurement determined with a real measurement system using method A of the GUM. With the presented method, it is possible to calculate an optimal measurement position within the measurement volume, based on a minimum uncertainty of measurement. Thereby, the influence of the operator related to the uncertainty can be significantly reduced.