Conversion of ACIS file to STEP Exchange file

Project Background

We have developed a CAD model translator and included it in the VM ( Virtual Manufacturing ) Web site in order to demonstrate the feasibility of making generic VM tools availabl e to designers and planners over the Internet. We chose this example for two reasons. First, CAD model translators from application-specific formats to a neutral one (such as STEP) are necessary for product data exchange between heterogeneous manufactur ing applications. Secondly, it is possible with current technology to provide such services over the Internet, since the information exchange between sites involves simple file transfers.

ACIS is a powerful solid modelling kernel used in many CAD systems, such as AutoCad and Microstation. It uses typical entities for the boundary repr esentation of a solid, including bodies, lumps, shells, faces, edges, loops, vertices, surfaces, directions and points. For data archival it stores this information in files in a special format ( ACIS .sat files ). STEP is the international standard for product data exchange(ISO 10303), and defines generic as well as application specific information models. Examples of the former include geometry and topology models while examples of the latter include application protocols for printed circuit assemblies of NC process plans for machined parts.

The STEP entities for geometry and topology are similar to the ones used by ACIS for shape representation; however, certain basic differences exist in the contents and format of these entities as well as in the structure of the two information models. A s a part of an ongoing project in the Optimal Selection of Partners in Agile Manufacturing (OSPAM) we have studied these differences, determined ways to construct one information model given t he data of the other, and have built ACIS to STEP and STEP to ACIS translators for boundary representations. In doing so, we have used the STEP standard to define the schema of an Object Oriented database (OODB), in which the STEP information models are stored. The ACIS to STEP translator accepts an ACIS .sat file, performs the necessary information transformation and stores the results in the STEP OODB; the reverse is performed by the STEP to ACIS translator.

For this VM project, the ACIS to STEP translator has been extended to accept ACIS .sat files and provide STEP files. In addition it can be called from the VM Web site, made to accept an ACIS sat file from a remote site and return a STEP file to that remo te site. Figure (1) describes the functionality of the extended translator. A user from a remote site may call the translator by clicking on the VM Web site. In response the user will be taken to the web site at which the translator description is prese nt. The remote user can then access the user manual or the translator directly from the translator web site by clicking on the appropriate hypertext. The translator routine then reads the appropriate ACIS .sat file, performs the necessary data transformations and populates the STEP OODB database. Subsequently, a file generator routine accesses this OODB and converts into the STEP file. The STEP file is then both displayed on the screen and sent to the user by email.

Limitations of this translator

The scope of this translator is limited to shapes with planar, cylindrical and conical surfaces only. All other surfaces will not be processed by this translator.

Product Example

To demonstrate the ability of the translator we have included an example (cube with a cylindrical through hole) of a STEP file which has been translated from an ACIS .sat file usin g the UMCP/ACIS-STEP translator.

How to use the translator?

• Read the user's manual to get step by step instructions on using the translator.

• Run the translator.

Feedback

• Please provide us suggestions, comments, and bug reports.

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Institute for Systems Research - November 17 1995 - webmaster@isr.umd.edu

@ The Institute for Systems Research, University of Maryland will not take any responsiblity for the consequences resulting from the use of the translator. Users access the translator at their own risk.