Development of a Step-based Dimensioning and ... - CiteSeerX

Proc. Natl. Sci. Counc. ROC(A) Vol. 22, No. 6, 1998. pp. 831-840

Development of a Step-based Dimensioning and Tolerancing Data Model J HY -C HERNG TSAI, T SAN -C HAO CHUANG,

AND

D E-N ING GUO

Department of Mechanical Engineering National Chung-Hsing University Taichung, Taiwan, R.O.C. (Received January 14, 1998; Accepted April 23, 1998) ABSTRACT STEP (STandard for the Exchange of Product model data) is an effort by the International Organization for Standardization (ISO) to develop an international standard for product modeling required for industrial automation. The product model involves both generic working standards and information models. As product accuracy becomes tighter, dimensioning and tolerancing (D&T) information also plays an important role in the product lifecycle. It is, therefore, important to develop a D&T data model based on STEP. This paper investigates the information required to build a STEP-based D&T schema and describes the development and implementation of such a D&T data model. It is found that the ISO draft model is not capable of representing the mating relationship between parts; hence, additional entities to model this relationship are suggested. Construction of a product D&T specifications based on the developed model is then described. Two examples, including a single part with an interface for constructing the corresponding tolerance network and an assembled product with D&T and mating specifications, are given to illustrate how the developed data model can be used in engineering practice. Key Words: STEP, product model, dimensioning and tolerancing, data model, ISO 10303

I. Introduction Due to the fast pace of technology and growing competition in the global marketplace, the lifecycle of a product has been greatly shortened, thus causing the development cycle from conceptual design to market to be highly reduced. One of the solutions to this challenge is the concurrent engineering approach, in which the functionality, manufacturability, inspectability, and serviceability of a product can be analyzed and adjusted in the design stage through distributed teamwork and simultaneous processing. Problems can be identified and solved in the early stage before the design is sent to manufacturing and subsequent processes. The product development cycle can consequently be reduced. To achieve this goal, a unified and shared product model which supports product data for design, analysis, manufacturing, inspection, and service is required. The model must provide information for related analyses and applications of the product, in addition to geometric specifications (Ranky, 1994). As the requirement of accuracy becomes more important, tolerances play a critical role in product development. In engineering practice, accuracy is often controlled by the dimensioning and tolerancing (D&T)

assignment on a blue print. Although D&T specifications can be specified in an engineering drawing, the data associated with these specifications, however, are not supported in current CAD/CAE/CAM (ComputerAided Design, Computer-Aided Engineering and Computer-Aided Manufacturing) systems. As a result, such important data are not available for information sharing and reasoning in design, analysis, manufacturing, inspection, as well as assembly processes. In order to achieve a unified data model which supports activities in the product lifecycle, it is important to develop a D&T data model based on international standards.

1. Literature Review Early efforts in defining product specifications focused on engineering drawings and their completeness. IGES (Initial Graphics Exchange Specification) was the standard under this effort (ANSI, 1987). However, IGES only supports certain geometric data that only incompletely supports activities in the product lifecycle. To compensate for the inadequacy of the product information, the Department of Defense (DoD) of the United States of American started to develop CALS (Computer-aided Acquisition and Logistic Support) as a product data standard used by the DoD and

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J.C. Tsai et al. its vendors in the 1980s (Henderson, 1991). There were other efforts which tried to define a standard during the same period, including MAP (Manufacturing Automation Protocol) and PHIGS (Programmer’s Hierarchical Interactive Graphics System) (Howard, 1991). Among these proposed standards, CALS had the widest coverage and was most detailed. However, CALS still lacked product applications. Furthermore, it was originally developed for military purposes and needed further modification for use in industry. Following this early progress, the International Organization for Standardization (ISO) formed the 184 Technical Committee (TC184: Industrial Automation Systems and Integration) with the goal of defining an international product data model, called the STEP (STandard for the Exchange of Product model data) standard or ISO 10303. The standard is described in a structured language called EXPRESS, also a part of ISO 10303. The product model consists of several parts, including the kernel and application protocols as well as validation tests and implementation methods (ISO, 1994). The basic structure and requirements of the standard were discussed and modified at a meeting in Tokyo in late 1988 (ISO, 1989). Since then, researchers and industry experts (e.g., Bloor and Owen, 1991; Curran, 1994; Gu and Chan, 1995; Schenck and Wilson, 1995) have been working together to define the standard better. Several drafts of the standard have been approved by ISO members and formally published. Some STEP centers, including those in the USA, UK, France, Germany, Japan, and China, were established and joined the effort. The US Department of Commerce (DoC) also joined the effort and modified the PDES (Product Data Exchange Specification) project in 1992. At the same time, DoC and DoD together announced their commitment to developing and promoting the standard. They strategically require that product specifications used in the two departments have to meet the standard. Furthermore, CALS was afterwards developed from its original military purpose into a methodology and tools for enterprise management under different names, such as Continuous Acquisition and Logistic Support and Commerce At Light Speed. However it still lacked product models and applications for industry. To remove this gap, CALS employs STEP as its standard for product definition to model detailed product information, in particular for use in CAD/CAE/CAM systems. The early D&T information model developed in STEP was based on the offsetting theory of Requicha (1983) and the virtual boundary theory of Jayaraman and Srinivasan (1989). As the tolerance model is related to the geometric model, work has focused on representing tolerancing information associated with

Fig. 1. Structure of the STEP product model.

geometry information, including the efforts made by Roy and Liu (1988), Shah and Miller (1990), and Lu and Wilhelm (1991). Others, such as Tsai et al. (1992) and Liu and Fischer (1995) have investigated D&T information associated with assembly models. Feng and Yang (1995) presented a draft of the STEP D&T data model as part of their involvement in the PDES/ STEP (Product Data Exchange using STEP) project. Basic information for the model is discussed in their article along with three developed schemes. Since the draft combines efforts made in research and industry, it forms a foundation for further investigation. This paper is based on the data model developed by Feng and Yang (1995) with further modification and revision from the standpoint of assembly. Examples are given to illustrate the use and application of the model.

2. Structure of the STEP Product Model The STEP product model consists of four layers as shown in Fig. 1. In the center, the model defines the standard description language, EXPRESS and related languages in parts 11 to 19. The kernel of the model consists of integrated resource models, including generic resource models and application resource models. Integrated generic resource models, numbered from 41 to 99, are those generally required for product data, such as fundamentals, geometry and topology, product structure, and tolerances. Integrated application resource models, on the other hand, consist of parts 101 to 199, which are commonly required for product data but are more application oriented including draughting, finite element analysis, and kinematics. As

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STEP-based D&T Data Model an information model, the standard also defines the implementation methods and conformance testing methodology. Implementation methods, such as the data exchange structure and format, data access interface, and mapping among different software languages, are numbered as parts 21 to 29. The conformance testing methodology, including abstract test suites and methods, requirements placed on testing clients, and general concepts, are defined in parts 31 to 39. Around the kernel, application protocols of models, such as associative draughting, configuration-controlled design, and the product life cycle, are defined based on the integrated resource models and implementation methods. As the number of applications can grow to be large, parts 201 to 1199 are reserved for their use. Applications of abstract tests based on the conformance testing methodology are still under development. Parts 1201 to 2199 are reserved for this purpose. This paper describes the development of a STEPbased D&T data model. In the following sections, the STEP D&T draft data model is first investigated, followed by presentation of a proposed model used to compensate for the missing assembly relationship among the parts. Implementation of such a data model and construction of the D&T specifications of a product based on these models are then described in Section III. Two examples, including a single part with an interface used to construct a tolerance network for a

tolerance analysis application and an assembled product, are given to illustrate the use of the schema in Section IV with conclusions following.

II. A Proposed Dimensioning and Tolerancing Data Model Geometric D&T specifications constitute the designed functional and behavior requirements of a product. These specifications also imply required manufacturing and inspection processes to carry out such requirements. Furthermore, the tolerance specifications are assigned to meet product function, part manufacturability, part interchangeability, and design robustness. Therefore, a D&T data model must be capable of supporting product design, analysis, manufacturing, inspection, and service. We will first discuss the information required for such a model. In the product development stage, the required D&T information is related to the parts and their relationships, in particular, the geometric feature, part assembly, and part D&T information. Such information includes the relative locations of parts and features in addition to the part geometry. The information consists of geometric shapes and dimensions, geometric dimensioning and tolerancing, limits and fits, and interval and statistical tolerances. Tolerances, which specify the allowable variation

Table 1. Classification of Tolerances tolerance item Linear size tolerance Angular size tolerance Diameter/Radius tolerance

classification (based on constraint) size tolerances

single-feature tolerances

Flatness Straightness Circularity Cylindricity

shape tolerances

Profile of line Profile of surface

profile tolerances

Perpendicularity Angularity Parallelism

orientation tolerances

Circular run-out Total run-out

run-out tolerances

Position Concentricity or Coaxiality Symmetricity

classification (based on feature)

location tolerances

Source: Tsai et al. (1995).

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single-feature or related-feature tolerances

related-feature tolerances

J.C. Tsai et al. Table 2. Basic D&T Information in the STEP Draft Model Element

Component

dimension value dimensioned feature

magnitude, unit one feature two feature

shape aspect shape aspect

measure path

linear, curvilinear, angular

plus minus tolerance

tolerance value

limit and fit

grade, deviation, fitting type

statistical tolerance

type of distribution function

tolerance value

magnitude, unit

tolerance type

a list of text strings

toleranced feature

shape aspect

tolerance zone form

a list of all possible forms of tolerance zones used in geometric tolerancing

material condition

MMC, LMC, RFS

datum reference

a set of datums

datum

shape aspect

datum feature

shape aspect

datum target

shape aspect

composite tolerance

two geometric tolerances

Source: Feng and Yang (1995).

of geometric constraints, are treated as special attributes of geometric constraints. Such constraints and tolerances can be classified according to the nature of constraints, or according to the way they constrain features. Table 1 lists different kinds of tolerances used in engineering practice (ASME, 1994; ISO, 1983). It shows that tolerances can be classified either based on the nature of the associated constraints, such as the size, shape, orientation or location, or based on the way in which they constrain features, i.e., single-feature or related-feature tolerances. From the standpoint of constraint management, the latter is better since it is better defined and easier to implement. Conventional size tolerance (plus-minus tolerance) is related to limit and fit and is treated as a kind of single-feature tolerance in Table 1 (Tsai et al., 1995).

1. D&T Draft Model in the STEP D&T specifications are often treated as part of the geometry in a design. These specifications are assigned in the design process based on the level of abstraction. During conceptual design in the early design stage, a designer works with nominal dimensions, i.e., dimensions without variation. Tolerances, except limits and fits, are not considered until manufacturing and costs

are taken into consideration. Information associated with the process, therefore, is required in the D&T data model. Table 2 lists the basic elements of the STEP D&T draft model proposed by Feng and Yang (1995). These elements are then used to construct data structures in the STEP D&T draft data model. However, two other elements, the part relationship and datum reference frame (DRF), are required in design practice; thus, they should also be treated as basic items in D&T assignment. Details of the two items will be discussed in the following section. Although the tolerance model of STEP (part 47: Tolerances) has not yet been published, the project participants have discussed the draft in Feng and Yang (1995). In that article, the proposed model uses three schemes to define required data structures. They are shape_dimension_schema, shape_tolerance_schema, and shape_aspect_schema. Graphic representations of the three schemes in EXPRESS-G are attached in Appendices for reference. The first schema describes the dimension and relative position of a product, corresponding to the first seven elements shown in Table 2. This schema consists of two parts. One part describes the magnitude and unit of dimensioning and the other one describes dimensioned geometric entities and their relative positions. The second schema mainly describes the data structure for dimensional and geometric tolerances, corresponding to the remaining elements shown in Table 2. It defines data structure in accordance with the classification of tolerances as presented in Table 1. Tolerances are defined as two entities, “geometric_ tolerance” and “geometric_tolerance_with_datum”. As discussed in the previous section, tolerances can be classified into two groups thus single-feature tolerances can be established based on the former entity while related-feature tolerances can be instanced based on the latter entity. The data structure of the first entity is defined based on the required elements shown in Table 2. The latter, however, requires a datum reference and is defined as a “child” of “geometric_tolerance”; therefore, it inherits predefined attributes besides elements in the datum system. As the first two schemes refer to geometric entities, or “shape_ aspect” in STEP, the third shema is based on shape_ aspect in order to define datum_system related entities, such as datum, datum_feature, and datum_target_ feature.

2. Additional Information Required for the D&T Data Model

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In addition to the basic information required for

STEP-based D&T Data Model Table 3. Definition and Description of the Entities Part, DRF, and Matting_relationship Definition of Entity

Description of Attributes

ENTITY part name : label; of_product : product_definition; feature_component : SET OF [1:?] shape_aspect; END_ENTITY;

Name is the name of the product. Of_product is the product name that this part belongs to. Feature_component is the set of the features that belong to this part.

ENTITY datum_reference_frame name : label; of_part : part; components : LIST OF [1:?] shape_aspect; END_ENTITY;

Name is the name of the DRF. Of_part represents the part name to which this DRF belongs. Components is a sequence of datums that are used to construct this DRF.

ENTITY matting_relationship; name : label; matting_constraint : matting_type; related_part : SET OF [1:2] part; shape_aspect_applied_to : SET OF [1:?] shape_aspect; END_ENTITY;

Name is the name of this relationship. Mating_constraint represents one of the defined mating types. Related_part is the set of parts that is constrained by this constraint (relationship). Shape_aspect_applied_to means the set of shape_aspects that is constrained by this relationship.

the STEP D&T draft model, other information is required for the D&T of a product. Considering that a product is a combination of parts, it is essential for a data model to be able to represent the relationships between the parts. As opposed to relationships among shape_aspects defined in STEP, it is necessary to define an entity that describes part relationships. Meanwhile, the attributes of the entity “part” must be able to recognize such a relationship in an assembly. That is, an entity that is capable of showing the matting relationship is needed, and modification of the entity “part” is required to accommodate this information. Another item of required information for the model is the DRF. A DRF is a set of datums that establish a common frame for D&T in a part. DRF is an important geometric entity used to set up a part in manufacturing and inspection. It is, therefore, a required item of basic D&T information in the product model. In other words, at least one DRF is required in a part. Furthermore, a datum should be a basic geometry entity, i.e., a shape_aspect, that can be used as a reference datum for manufacturing and inspection. As a result, two entities, “datum_reference_frame” and “matting_relationship”, are created along with the entity “part” modified in the proposed model. Data structures for the three entities are listed in Table 3 with graphic representation shown in Fig. 2. Together with the D&T model drafted by ISO, the proposed additional D&T model establishes a more complete D&T model that is capable of providing the required D&T information used in activities in the product lifecycle.

Fig. 2. EXPRESS-G representation of the additional D&T data model.

III. Implementation According to STEP, three methods can be used for the implementation defined in parts 21 to 23. Part 21 defines a neutral text file for data exchange, sometimes called the STEP physical file. Part 22 defines a standard data access interface (SDAI) for accessing the data model. Part 23 is more application orientated and defines C++ programming language binding to the SDAI specification. In this paper, we use the last method to implement the data model and to construct product data with output in compliance with the STEP physical file defined in part 21. To use the D&T data model discussed in the previous section, we first establish a class library by compiling related data models, including the schemes from STEP parts 41, 42, 43, and 47, and additional schemes defined in the previous section. To compile these data models, a CASE (Computer-Aided Software Engineering) tool, the ST-Developer, is used in the developing process. Data models are first compiled

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J.C. Tsai et al. tolerance value, the feature toleranced, and the type of tolerance region. A related-feature tolerance requires a datum_reference in addition to the above information. A datum_reference consists of its notation (name), its datum_feature, and its order in the datum_system. The DRF of a part is also constructed in this stage.

IV. Examples

Fig. 3. Flow chart used to construct the STEP D&T data model and product D&T data.

As the developed D&T data models can be applied to a product as well as to a part, two examples, a single part and an assembled product, are given here to illustrate its application in engineering practice. In the first example, a single part with dimensional tolerances and geometric tolerances, including both self-reference and cross-reference tolerances, is used to show the capability of the data model. The DRF of the part is also established as a datum_reference_frame for dimensioning and tolerancing. The other example, a

into C++ class source codes by an EXPRESS compiler, and are then compiled into a class library by a C++ compiler, as shown in Fig. 3. The classes constructed in the library are then used by user-defined product D&T data. Figure 3 shows the process for constructing the class library and product data. The process used to construct the product data includes constructing part geometric shape data, part matting data, and part D&T data. Part geometric shape data is constructed using Constructive Solid Geometry, defined in ISO 10303 part 42: Geometric and Topological Representations. The defined geometric entities (single or composite CSG primitives) are linked to the attribute feature_component in the entity “part” defined in the previous section. Part matting data is based on the entity “matting_relationship” discussed in Section II. A matting relationship points to shape_aspects that match together. The matting condition can be a fitting (e.g. peg-in-hole), a planar match (e.g. face contact), or a special contact (e.g. socket) with associate attributes. Part D&T data comprises dimensioning data, the dimensional tolerancing data, and geometric tolerancing data. Dimensioning data consists of the value, dimensioned shape feature, and the location of the feature. Dimensional tolerancing data is defined by “plus_minus_tolerance”. It contains tolerance_range or limits_and_fits, depending upon the feature and mating relationship it applies. The attribute toleranced_dimension in the entity is used to identify the toleranced shape features and their relative positions. Geometric tolerancing data, on the other hand, is defined based how it is classified, as shown in Table 1. A single-feature tolerance contains data about the − 836 −

Fig. 4. Example 1, a single part.

STEP-based D&T Data Model ERENCE (‘position_tolerance’, #1320, (#960)); #1410 = GEOMETRIC_TOLERANCE (‘circularity_tolerance’, #1300); #1440 = SHAPE_ASPECT (‘datumA’, ‘’, $, .F.); #1450 = SHAPE_ASPECT (‘datumB’, ‘’, $, .F.); #1460 = SHAPE_ASPECT (‘datumC’, ‘’, $, .F.); #1470 = DATUM_REFERENCE_FRAME (‘A_DRF1’, $, (#1440, #1450, #1460));

Fig. 5. The tolerance network of example 1.

simplified manipulator, consists of several parts. This example illustrates how the relationship between the parts can be constructed using the developed data model. A STEP-formatted neutral file, as defined in part 21: Clear Text Encoding of the Exchanges Structure, is also presented for discussion.

1. Single Part Example Figure 4 shows a simple part with holeA and holeB in a rectangular block. HoleA is positioned with respect to the DRF established by datums A, B, and C, while the location of holeB is based on datum A and holeA (labeled as D). Both dimensional and geometric tolerances are applied to the two holes as shown in the figure. This information is constructed by following the process described in Section III. The product data is then saved to a text file following the format defined in STEP part 21. A portion of the 146-line product data is listed below: #200 #340 #900 #960 #1030 #1050 #1120 #1140 #1210 #1230 #1300 #1320 #1370

= SHAPE_ASPECT (‘holeB’, ‘ ‘, $, .F.); = SI_UNIT (*, .MILLI., .METRE.); = DATUM (‘holeA’, ‘primary’, $, *, ‘ D ‘); = DATUM_REFERENCE (#900, 1); = MEASURE_WITH_UNIT (LENGTH_MEASURE (0.06), #340); = MEASURE_WITH_UNIT (LENGTH_MEASURE (0.1), #340); = SIMPLE_TOLERANCE_ZONE (‘The tolerance zone is limited by two concentric circles separated by t’); = SIMPLE_TOLERANCE_ZONE (‘The tolerance zone is limited by a circle of diameter t’); = TOLERANCE_ZONE (#1120); = TOLERANCE_ZONE (#1140); = TOLERANCE_ELEMENT (#1030, #200, #1210); = TOLERANCE_ELEMENT (#1050, #200, #1230); = GEOMETRIC_TOLERANCE_WITH_DATUM_ REF-

Line #1370 defines the position tolerance applied to holeB with respect to hole A in a circular tolerance region of diameter 0.1mm. HoleB, the applied shape feature, is defined in line #1320, where #200 points to the name of the feature. The datum feature, holeA, of the tolerance points to #960. The tolerance specification is defined in #1320, #1050, and #340. The tolerance zone of the specification is defined in #1320 by the pointer #1230, which points to #1140. The DRF of this part is established by the datums A, B, and C, as can be found in lines 1470 and 14401460. The above data can be managed to construct a tolerance network (Tsai and Cutkosky, 1997) for application in tolerance analysis. In the network, shape features are represented as nodes and geometric D&T specifications are represented as arcs that connect nodes. As discussed in Section II, tolerances are classified as single-feature and cross-feature tolerances. A single-feature tolerance forms a loop around the shape feature to which it applies while a cross-feature tolerance links the feature to which it applies to a corresponding datum feature. Therefore, the tolerance network of this example can be represented as shown in Fig. 5 and can be retrieved from the output STEP physical file. As tolerance analysis is not within the scope of this paper, we will only briefly describe the process of constructing the network. One way to construct the network is to first tolerance specifications defined by the entities geometric_tolerance and geometric_ tolerance_with_datum_reference. As discussed in Section II, the former represents a single-feature tolerance and, thus, forms a loop around the feature to which it applies. In this example, line #1410 shows a circularity tolerance by pointing to line #1300, which shows that this tolerance specification is 0.06mm and is applied to feature holeB by tracing back to lines #1030, #340, and #200. Geometric_tolerance_with_ datum_reference, on the other hand, represents a crossfeature tolerance that links the feature, to which it applies, to datum features. In this example, line #1370 shows a position_tolerance applied to holeB with datum feature holeA. This is constructed by tracing line #1370 back to lines #1320, #1050, #340, #200, #960,

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J.C. Tsai et al. way. It also shows that these parts are decomposed from the product ‘simplified_robot’ defined in #5850. The tolerance network corresponding to this product is constructed by connecting the network of each part by means of mating_relationships among them. The above two examples show that the added scheme in the modified D&T data model is part of the basic information of the product definition. Application interfaces, such as the tolerance network for tolerance analysis, can be developed based on the basic product definition.

V. Conclusion Fig. 6. Example 2, a simplified robot with assembled parts.

and #900. This process is implemented by means of recursive algorithms to construct the tolerance network of each part based on its D&T data model.

2. An Assembled Part Example Figure 6 is a simplified manipulator with nine parts assembled together. The parts are mutually allocated with matting constraints between them. Product data is constructed following the process described in Section III with parts decomposed from the product as well as the matting relationships between the parts. The data is then saved to a STEP-format text file. A partial list of the 642-line data file is listed as the following for discussion of the matting relationship. #5850 #6040 #6050 #6060 #6070 #6080 #6090 #6100 #6150 #6160 #6380

= PRODUCT(“,‘manipulator’,‘simplified robot’,$); = SHAPE_ASPECT(‘partD_cylinder1’,“,$,.F.); = PART(‘partD’,#5850,(#6040)); = SHAPE_ASPECT(‘partE_blockA’,“,$,.F.); = SHAPE_ASPECT(‘partE_slotA’,“,$,.F.); = SHAPE_ASPECT(‘partE_hole1’,“,$,.F.); = SHAPE_ASPECT(‘partE_hole2’,“,$,.F.); = PART(‘partE’,#5850,(#6060,#6070,#6080,#6090)); = SHAPE_ASPECT(‘partF_cylinder1’,“,$,.F.); = PART(‘partF’,#5850,(#6150)); = MATTING_RELATIONSHIP(‘shaft_hole_matting’,. SHAFT_HOLE.,(#6050,#6100),(#6040,#6080)); #6390 = MATTING_RELATIONSHIP(‘shaft_hole_matting’,. SHAFT_HOLE.,(#6100,#6160),(#6090,#6150));

This partial list shows the matting relationship between part E and parts D and F as shown in Fig. 6. Line #6380 defines the relationship between parts D and E, identified in #6050 and #6100, as a shaft_hole_ matting with matting features partD_cylinder1 (#6040) and partE_hole1 (#6080). Line #6390 defines the matting relationship between parts E and F in the same

As STEP is becoming an international standard for product data exchange and serves as the product data standard for CALS, it is important to develop a STEP-based data model to serve industry needs. This paper has investigated the current D&T draft model developed by the participants of the PDES/STEP project (Feng and Yang, 1995) and proposed a STEP-based D&T data model in order to compensate for the inadequate capability of the draft model. These models are implemented in compliance with STEP part 23. The proposed model, together with other STEP models, can be accessed by other applications via a languagebounded interface, as defined in part 23. Two examples, a single part with an interface used to generate a tolerance network and a product with assembled parts, have illustrated the use and application of the data model. The two examples showed that the proposed D&T data model can provide D&T information required in product definition. It has also been shown that application interfaces can be developed based on the models. As STEP is becoming an international standard for product data exchange, further efforts is needed to make it more complete and more widely used. However, as the schemes of STEP are inter-connected and complicated, EXPRESS-G and IDEF-based diagrams are useful representations for those not familiar with but interested in STEP to obtain a quick understanding of the schemes. Furthermore, as the data model proposed in this article is implemented based on language-bounded method, it is suggested that future development should be based on platformindependent approaches, such as JAVA-based algorithms and SQL(Structure Query Language)-based databases.

Acknowledgment Funding for this research was supported by the National Science Council, R.O.C., under contract NSC 85-2612-E005-001.

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STEP-based D&T Data Model

Appendix 1

Appendix 2

EXPRESS-G Representation of the shape_ dimension_schema in the STEP D&T Draft Model.

EXPRESS-G Representation of the shape_ tolerance_schema in the STEP D&T Draft Model.

Appendix 3 EXPRESS-G Representation of the shape_aspect_ definition_schema in the STEP D&T Draft Model.

References ANSI (1987) Initial Graphics Exchange Specification: Digital Representation for Communication of Product Definition of Data. ANSI Y14.26-M, The American National Standard Institute, New York, NY, U.S.A. ASME (1994) Dimensioning and Tolerancing. ASME Y14.5M, The American Society of Mechanical Engineers, New York, NY, U.S.A. Bloor, M. S. and J. Owen (1991) CAD/CAM product data exchange: the next step. Computer Aided Design, 23(4), 237-243. Curran, L. (March 1994) STEP bridges the way to better product modeling. Machine Design, 137-140. Feng, S. C. and Y. Yang (1995) A dimension and tolerance data model for concurrent design and systems integration. Journal of Manufacturing Systems, 14(6), 406-426. Gu, P. and K. Chan (1995) Product modelling using STEP. Computer-Aided Design, 27(3), 163-172. Henderson, L. R. (1991) CALS as a solution for digital delivery of technical documents. Computer-Aided Design, 23(4), 252256.

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J.C. Tsai et al. Howard, T. L. J. (1991) Evaluating PHIGS for CAD and general graphics applications. Computer-Aided Design, 23(4), 244-251. ISO (1983) ISO 1101: Technical Drawings-Geometrical Tolerancing. International Organization for Standardization, Geneve, Switzerland. ISO (1989) ISO STEP Baseline Requirements Document, Tokyo Version. International Organization for Standardization, Geneve, Switzerland. ISO (1994) ISO 10303-1, Industrial Automation Systems and Integration − Product Data Representation and Exchange − Part1: Overview and Fundamental Principles. International Organization for Standardization, Geneve, Switzerland. Jayaraman, R. and V. Srinivasan (1989) Geometric tolerancing: I. virtual boundary requirements. IBM Journal of Research and Development, 33(2), 105-124. Liu, T. H. and G. W. Fischer (1995) An assembly code classification and coding scheme based on a STEP mechanical product model. Manufacturing Review, 8(1), 33-46. Lu, S. C. Y. and R. G. Wilhelm (1991) Automating tolerance synthesis: a framework and tools. Journal of Manufacturing Systems, 10(4), 279-296. Ranky, P. G. (1994) Concurrent engineering and enterprise modelling. Assembly Automation, 14(3), 14-21.

Requicha, A. A. (1983) Toward a theory of geometric tolerancing. International Journal of Robotics Research, 2(4), 45-60. Roy, U. and C. R. Liu (1988) Feature-based representational scheme of a solid modular for providing dimensioning and tolerancing information. Robotics and Computer− Integrated Manufacturing, 4(3/4), 335-345. Schenck, D. A. and P. R. Wilson (1995) Information modeling the EXPRESS way. Manufacturing Review, 8(2), 155-163. Shah, J. J. and D. W. Miller (1990) A structure for supporting geometric tolerances in product definition systems for CIM. Manufacturing Review, 3(1), 23-31. Tsai, J. C. and M. R. Cutkosky (1997) Representation and reasoning of geometric tolerances in design. Artificial Intelligence in Engineering Design, Analysis, and Manufacturing, 11(4), 325341. Tsai, J. C., D. N. Guo and K. D. Cheng (1995) Variational kinematic models for geometric tolerances and fittings. Proceedings of the 4th National Applied Mechanisms and Robotics Conference, paper AMR95-107. Cincinnati, OH, U.S.A. Tsai, J. C., R. Konkar, and M. R. Cutkosky (1992) Issues in incremental analysis of assemblies for concurrent design. In: Artificial Intelligence in Design ’92, pp. 617-635. J. Gero Ed. Kluwer Academic Publishers, Dordrecht, the Netherlands.

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