STEP Modified

Click to edit Master title style

Neutral File FormatsCADPresentation 1Prepared by: Ahmed Hassan Ibrahim Mustafa Sherif IbrahimPrepared to: Dr. M. Awad

MANF 2014

Ain Shams UniversityFaculty of EngineeringNew Programs

Manufacturing Engineering Program2ContentIntroductionNeutral file formatsImport File FormatsSTEPSTEP structureExampleAdvantages

Introduction A large number of applications are used In CAD/CAM, which are manufactured by different vendors. Therefore, there is a need to establish standards in CAD that help in linking different hardware and software systems from different vendors to be integrated to serve the requirements of the industry. With the proliferation of computers and software in the market, it became necessary to standardize certain elements at each stage, so that investment made by companies in certain hardware or software was not totally lost and could be used without much modification on the newer and different systems. Standardization in engineering hardware is well known. Further, it is possible to obtain hardware and software from a number of vendors and then be integrated into a single system. This means that there should be compatibility between various software clement? as also between the hardware and software. This is achieved by maintaining proper interface standards at various levels. The following arc some of them.

4Neutral file formatsNeutral files and neutral file interfaces are needed in order to exchange product data between CAD systems. Also direct translators exist but the number of needed translators is becoming large if there are many CAD systems involved in the data transfer. A neutral CAD file is a CAD format, generally governed by a commercial, government or international standard and is open source. Many can write it, and many can read it. It is not a CAD specific, proprietary format.5

Situation with direct data transfer

FIG 5.6 Data interchange method between two different CAD systems using neutral data format such as IGES or STEP

For each pair of CAD systems to be communicated two translators are required, one for each direction.

With proliferation of computers (o do a number of tasks related to design and manufacturing, n becomes a necessity to have a means of communication between the various systems in the same plant or between different plants. Since the CAD/CAM software is available from a number of vendors, it becomes necessary that there should be a means by which different systems are able to interchange information to avoid the duplication of effort involved in the geometric model creation, which often happens to be the highest.This means that the data format used by all the software should be the same. However, as explained earlier, the database formats are identified on the basis of the modelling requirements and is therefore not possible to have identical format for all the systems. However, it is possible to identify a certain format for drawing exchange and make it a standard so lhat the various systems can convert their internal format to this standard format or vice versa as shown in Fig. 5.4. 6

situation of the data transfer using a neutral file format. Using a neutral file format only one pre- and post-processor is needed for each CAD system.7Import File FormatsA number of neutral file formats are provided. Here is a list of file extensions and the source that the data may come from:.dxf Neutral 2D fie format.igs, .ige, .iges Neutral 3D surface fie format.stp, .ste, .step Neutral 3D solid fie format.xgl, .zgl Neutral 3D graphic viewing format

Standard for the Exchange of Product Model Data (STEP)Standard for the Exchange of Product Model Data (STEP), officially the ISO standard 10303. Product Data Representation and Exchange, is a series of international standards with the goal of defining data across the full engineering and manufacturing life cycle.

structure it is easy to read with typically one instance per line.

The ability to share data across applications, across vendor platforms and between contractors, suppliers and customers, is the main goal of this standard.

The development of STEP started in 1984 as a world wide collaboration. The goal was to define a standard to cover all aspects of a product (i.e. geometry, topology, tolerances, materials, etc.), during its life time.

necessary to completely define a product for the purposes of design, analysis, manufacture, test, inspection and product support.

10STEP files are created from converting the proprietary design geometry into solids and surfaces

Proprietary CAD formatSTEP formatTo generate STEP files, different export options are available based on the CAD software being usedOptions include solids only, surfaces only, and assembly hierarchyA STEP file will typically have a smaller file size than the original CAD file for simple geometryLibrary parts such as nuts and bolts which are all thesame and used multiple times can greatly increase file size

11Overview of STEP process model

The STEP documentation is split into eight major areas:Overview It gives the general introduction and overview of the standard and forms part one of the ISO standard 10303.Overview and Fundamental Principles: defines the principles of STEP; Description Methods: the EXPRESS data modelling language which represents product information;

1-

-----2-Description Methods: EXPRESSIntegrated resources and application protocols are expressed using the EXPRESS data modelling language. It defines entities in terms of data and behavior. Data represents the properties of an entity and behaviour is represented by constraints. Entities are defined in terms of attributes. An attribute can be a simple data type or another entity type. If the attribute is an entity, it is a reference to this entity. Entity is a basic concept in EXPRESS.

14Description Methods The application protocols planned in STEP are far reaching compared to any other existing standard or models. Hence, a new descriptive formal information modelling language called EXPRESS is developed such that the protocols be properly defined.

An example of the EXPRESS specification of the entity circle, defined in the STEP

ENTITY circleSUBTYPE OF (conic); position : axis2_placement; radius : length_measure;DERIVE dim : INTEGER := coordinate_space(position);WHERE WR1 : radius > 0.0;END_ENTITY;Implementation Methods This provides specifications as to how the STEP information be physically represented for the exchange environment. This, therefore, refers to the actual implementation levels. Implementation Methods: contain the definitions of the physical representation of product information;Conformance Testing: a conformance testing methodology and framework;

3-Implementation MethodsImplementation methods specify the mapping of EXPRESS product information representation to physical format and are independent of the application protocol. At the moment, in STEP there are three implementation methods. These are:File Exchange: defines the physical file format syntax for the STEP data exchange. STEP file is an ASCII file where the information is separated using special characters and words;Application Programming Interfaces: SDAI (STEP Data Access Interface) specifies the services available to an application to acquire and manipulate the data which structure is modelled in EXPRESS. It also offers a set of functions to retrieve and manipulate STEP data. It is not important for an application to know how the data is stored or ordered;Database Implementations: defines the methods for implementing data storage and retrieval in databases.

--4- A lot of activities are going on to develop tools and data exchange applications for implementing STEP technologies. These applications, existing as public domain and commercial products, can be divided, for instance, as follows: STEP editors: help to edit and navigate along the STEP physical file. They check the syntax and internal consistency of the file;

EXPRESS editors and modellers: help to edit, create and navigate along EXPRESS models. They check the EXPRESS syntax and cross-references, and help to find entities and references to other entities;EXPRESS compilers: compile EXPRESS models into a programming language (e.g. C++ classes) or database application structures. They generate I/O-libraries which operate STEP physical files or databases which are equipped with SDAI;Conversion applications: convert one application protocol into another one. They convert also between IGES and STEP or DXF and STEP;STEP pre- and post-processors: to handle STEP file I/O in CAD systems.

174- Conformance and Tools This part provides the specifications for conformance testing of the processors used for STEP information. They provide information on methods for testing of software-product conformance to the STEP standard, guidance for creating abstract-test suites and the responsibilities of testing laboratories.

Integrated-generic Resources These contain the specifications of the information models that support various application areas that form part of STEP. The topics that form part of this specification are: geometric and topological representation, product structure organization, materials, visual presentation, tolerances, form features and process structure and properties. Integrated Resources: contain the definitions of representation of product information which are common for different application protocols;

Integrated Resources The part of the STEP standard which is defined in integrated resources is common to every application protocol and independent from implementation methods. Integrated resources offer concepts to different applications areas to use in their application protocols.

Integrated resources are divided in two parts: Integrated Generic Resources and Integrated Application Resources. Integrated generic resources are common to every application protocol and integrated application resources are common to application protocols of same type.

The different parts of integrated generic resources are: Fundamentals of Product Description and Support, Geometric and Topological Representation (STEP part 42), Representation Structures, Product Structure Configuration, Materials, Visual Presentation, Shape Tolerances, and Form Features. The different parts of integrated application resources are: Draughting, Ship Structures, Electrical Functional, Finite Element Analysis, and Kinematics.

19Application Information Models These specify the information models to be used for specific application areas such as draughting, finite element analysis, kinematics, building core model and Engineering analysis core. Application Protocols: contain the definitions of representation of product information which are specific to a particular application area;

7-Application Protocols Integrated resources are not sufficient to support product information of a specific application area without addition of more specific constraints and relationships. An application protocol is a combination of a suitable part of integrated resources with additional constraints and specific concepts of this particular application area. CAD systems have to use the same application protocol before they can exchange STEP data. Application protocols that currently are approved as an international standard are: Explicit Draughting [#ap201##1#] (AP-201) and Configuration Controlled Design [#ap203##1#] (AP-203). Application protocols under development are for instance: Associative Draughting, Mechanical Design Using B-Rep, Mechanical Design Using Surface Representation, Mechanical Design Using Wireframe, Sheet Metal Products, Life Cycle Product Changes Process, Design through Analysis of Composite and Metallic Structures, Printed Circuit Assembly: Design and Manufacturing, Printed Circuit Assembly: Test and Integrated Diagnostics and Re-manufacturing, Electrotechnical Plants, Numerical Control Processes for Machined Parts, and Automotive Mechanical Design.

20Application Protocols These are the main protocols to be used as subsets of STEP information model for exchange of data between specific application systems (such as between two finite element systems or between a CAD and Process Planning system).

Application Interpreted Constructs These relate to the specific resources useful for defining the generic structures useful for applications. These are reusable groups of information resource entities that make it easier to express identical semantics in more than one application protocol. Abstract Test Suites: abstract test cases for an application protocol to support the conformance requirements.22Examples include edge-based wireframe, draughting elements, constructive solid geometry, etc. These are given in part numbers 501 onwards. Examples include edge-based wireframe, shell-based wireframe, geometry-bounded 2D wireframe, draughting annotation, drawing structure and administration, draughting elements, geometry-bounded surface, non-manifold surface, manifold surface, geometry-bounded wireframe, etc.

23

STEP Application Protocol AP 203 Explicit Draughting

In order to support specific business functions, STEP contains a number of subsets known as Application Protocols (APs), which constrain the standard to a particular business context. STEP also supports a wide range of IT services, ranging from simple file exchange through databases and language bindings to XML and schemas. STEP does not constrain the process modeling tools which can be used to express the context of the information exchanges.

Deliverables Relevant STEP APs available for ASD deployment (see separate blips for more detail):AP203 for configuration controlled 3D data, including full PDM information, parametrics, and PMI (Geometric dimensioning and tolerancing, annotations, )AP209 for finite element analysisAP210 for electronic assembly, interconnect and packaging AP212 for electrotechnical design and installation AP214 for core automotive mechanical design AP224 for mechanical definition data for process planning based on form featuresAP232 for technical data packagesAP233 for systems engineering (under ballot as a Draft International standard)AP235 for Engineering properties for product design and verificationAP238 for NC machiningAP239 for Product Life Cycle Support (see separate blip on PLCS)

24STEP Application Protocol AP207 Configuration Controlled Design

25

Example for STEP file generation Sheet Metal Die Planning and Design

26Measurement in Product

ExampleISO-10303-21;HEADER;FILE_DESCRIPTION(/* description */ ('A minimal AP214 example with a single part'),/* implementation_level */ '2;1');FILE_NAME(/* name */ 'demo',/* time_stamp */ '2003-12-27T11:57:53',/* author */ ('Lothar Klein'),/* organization */ ('LKSoft'),/* preprocessor_version */ ' ',/* originating_system */ 'IDA-STEP',/* authorization */ ' ');FILE_SCHEMA (('AUTOMOTIVE_DESIGN { 1 0 10303 214 2 1 1}'));ENDSEC;HEADER section

As seen in the above example, the file is split into two sections following the initial keyword ISO-10303-21;:

The HEADER section has a fixed structure consisting of 3 to 6 groups in the given order. Except for the data fields timestamp and FILE_SCHEMA all fields may contain empty strings.

FILE_DESCRIPTION description implementation_level. The version and conformance option of this file. Possible versions are "1" for the original standard back in 1994, "2" for the technical corrigendum in 1995 and "3" for the second edition. The conformance option is either "1" for internal and "2" for external mapping of complex entity instances. Often, one will find here the value __'2;1'__. The value '2;2' enforcing external mapping is also possible but only very rarely used. The values '3;1' and '3;2' indicate extended STEP-Files as defined in the 2001 standard with several DATA sections, multiple schemas and FILE_POPULATION support. FILE_NAME name of this exchange structure. It may correspond to the name of the file in a file system or reflect data in this file. There is no strict rule how to use this field. time_stamp indicates the time when this file was created. The time is given in the international data time format ISO 8601, e.g. 2003-12-27T11:57:53 for 27 of December 2003, 2 minutes to noon time. author the name and mailing address of the person creating this exchange structure organization the organization to whom the person belongs to preprocessor_version the name of the system and its version which produces this STEP-file originating_system the name of the system and its version which originally created the information contained in this STEP-file. authorization the name and mailing address of the person who authorized this file. FILE_SCHEMA. Specifies one or several Express schema governing the information in the data section(s). For first edition files, only one EXPRESS schema together with an optional ASN.1 object identifier of the schema version can be listed here. Second edition files may specify several EXPRESS schema.

The last three header groups are only valid in second edition files.

FILE_POPULATION, indicating a valid population (set of entity instances) which conforms to an EXPRESS schemas. This is done by collecting data from several data_sections and referenced instances from other data sections. governing_schema, the EXPRESS schema to which the indicated population belongs to and by which it can be validated. determination_method to figure out which instances belong to the population. Three methods are predefined: SECTION_BOUNDARY, INCLUDE_ALL_COMPATIBLE, and INCLUDE_REFERENCED. governed_sections, the data sections whose entity instances fully belongs to the population. The concept of FILE_POPULATION is very close to schema_instance of SDAI. Unfortunately, during the standardization process, it was not possible to come to an agreement to merge these concepts. Therefore, JSDAI adds further attributes to FILE_POPULATION as intelligent comments to cover all missing information from schema_instance. This is supported for both import and export. SECTION_LANGUAGE allows assignment of a default language for either all or a specific data section. This is needed for those Express schemas that do not provide the capability to specify in which language string attributes of entities such as name and description are given. SECTION_CONTEXT provide the capability to specify additional context information for all or single data sections. This can be used e.g. for STEP-APs to indicate which conformance class is covered by a particular data section.

28DATA;#10=ORGANIZATION('O0001','LKSoft','company');#11=PRODUCT_DEFINITION_CONTEXT('part definition',#12,'manufacturing');#12=APPLICATION_CONTEXT('mechanical design');#13=APPLICATION_PROTOCOL_DEFINITION('','automotive_design',2003,#12);#14=PRODUCT_DEFINITION('0',$,#15,#11);#15=PRODUCT_DEFINITION_FORMATION('1',$,#16);#16=PRODUCT('A0001','Test Part 1','',(#18));#17=PRODUCT_RELATED_PRODUCT_CATEGORY('part',$,(#16));#18=PRODUCT_CONTEXT('',#12,'');#19=APPLIED_ORGANIZATION_ASSIGNMENT(#10,#20,(#16));#20=ORGANIZATION_ROLE('id owner');ENDSEC;END-ISO-10303-21;DATA section

The DATA section contains application data according to one specific express schema. The encoding of this data follows some simple principles.

Instance name: Every entity instance in the exchange structure is given a unique name in the form "#1234". The instance name must consist of a positive number (>0) and is typically less than 263. The instance name is only valid locally within the STEP-file. If the same content is exported again from a system the instance names may be different for the same instances. The instance name is also used to reference other entity instances through attribute values or aggregate members. The referenced instance may be defined before or after the current instance. Instances of single entity data types are represented by writing the name of the entity in capital letters and then followed by the attribute values in the defined order within parenthesis. See e.g. "#16=PRODUCT(...)" above. Instances of complex entity data types are represented in the STEP file by using either the internal mapping or the external mapping. External mapping has always to be used if the complex entity instance consist of more than one leave entity. In this case all the single entity instance values are given independently from each other in alphabetical order as defined above with all entity values grouped together in parentheses. Internal mapping is used by default for conformance option 1 when the complex entity instance consists of only one leave entity. The encoding is similar to the one of a single entity instance with the additional order given by the subtype definition. Mapping of attribute values: Only explicit attributes get mapped. Inverse, Derived and re-declared attributes are not listed since their values can be deduced from the other ones. Unset attribute values are given as "$". Explicit attributes which got re-declared as derived in a subtype are encoded as "*" in the position of the supertype attribute. Mapping of other data types: Enumeration, boolean and logical values are given in capital letters with a leading and trailing dot such as ".TRUE.". String values are given in " ". For characters with a code greater than 126 a special encoding is used. The character sets as defined in ISO 8859 and 10646 are supported. Note that typical 8 (e.g. west European) or 16 (Unicode) bit character sets cannot directly be taken for STEP-file strings. They have to be decoded in a very special way. Integers and real values are used identical to typical programming languages Binary values (bit sequences) are encoded as hexadecimal and surrounded by double quotes, with a leading character indicating the number of unused bits (0, 1, 2, or 3) followed by uppercase hexadecimal encoding of data. It is important to note that the entire binary value is encoded as a single hexadecimal number, with the highest order bits in the first hex character and the lowest order bits in the last one. The elements of aggregates (SET, BAG, LIST, ARRAY) are given in parentheses, separated by ",". Care has to be taken for select data types based on defined data types. Here the name of the defined data type get mapped too. See also "Mapping of Express to Java" for more details of this.[clarification needed]

29Advantages of STEPSTEP files will reliably transfer simple solids and surface geometrySTEP translators are available for most major CAD formatsOther neutral file types such as IGES cannot capture complex shapes without creating files of a huge size STEP files can be imported and exported into various CAD software to fix bad geometryProviding a single interface from a supplier to all their customers, reducing the cost of creating and maintaining multiple processes and tools.International standard facilitates collaboration with international partners and sales to international customersEnsuring that the product information flow is independent from the different software tools used to support the business processes, allowing organizations to select and update their systems without disrupting the complete network of services.Enabling information on a product to be maintained in a usable form over its full life cycle, which is often measured in decades, far longer than the software tools, operating systems and equipment used to create the information in the first place.

Use of a single integrated model to support different business functions with consistent information, avoiding the cost of synchronizing different information sources.Enforcement of information quality rules, avoiding costs arising from decisions made on inaccurate data.Translation to a standard form has additionally demonstrated significant improvements in information quality and cost reductions through early elimination of inconsistencies and errors

30

Original CAD 20 MBSTEP 10 MB IGES 35 MBMBSTEP 10 MBIGES35 MB31References:Cad/Cam: Prin & Appl 3E By Posinasetti Nageswara Raohttp://en.wikipedia.org/wiki/ISO_10303-21