Modelling Geometrical Tolerances with Intervals Using ISO-Standard STEP

A development of complex mechatronic systems requires a multitude of decentralised designing and processing systems. The various software and file formats which are involved in the development process need a quick and smooth data exchange via standardised data models and interfaces. The ISO 10303 norm STEP (STandard for the Exchange of Product model data) has been developed by the International Organisation for Standardisation (ISO) within the Technical Committee 184 “Industrial Automation System & Integration”. STEP provides a basic approach for an unambiguous representation of computer interpretable product information throughout the whole life-cycle of a product [1]. There are three key components of STEP: the EXPRESS data specification language is used to define data structures, entities, attributes, relationships and constraints together with EXPRESS-G, which is intended as a graphic representation of data models [10]. The Implementation Forms provide a physical file format for data that conforms to any EXPRESS schema and a Standard Data Access Interface (SDAI) to databases and applications. The Standard Data Models include integrated resources for almost universal applicability and specific models fulfilling the requirements of a particular industrial application. Around the kernel, the Application Protocols of models are defined, based on the integrated resources and implementation methods. Thus, the ISO-Standard STEP can be interpreted as a construction kit with application protocols, which use predefined elementary construction kits under specific rules and norm methods. An application protocol consists of three parts. The first part is the application activity model (AAM), which describes the functionality and life-cycle of a product using the SADT (Structure Analysis and Design Technique) method. The second part contains the application reference model (ARM). In this part the formal descriptions of the objects take place which are identified in AAM using the description language EXPRESS or EXPRESS-G. The Application Interpreted Model (AlM) stands at the end of the application protocol and concerns the mapping of the ARM-model into an