Part 2-3 - STEP NC-The End Of G-Codes

The First STEP

The biggest step in this direction has already been taken. It's STEP, the STandard for the Exchange of Product model data, a comprehensive ISO standard (ISO 10303) that describes how to represent and exchange digital product information. STEP replaces IGES as the means by which graphical information is shared among unlike computer systems around the world. The big difference is that STEP is designed so that virtually all essential information about a product, not just CAD files, can be passed back and forth among users.

The core of the standard is a library of engineering definitions that can be assembled into various "application protocols" customized for the product models needed by particular industries and activities. A common library covers geometry, topology, tolerances, relationships, attributes, assemblies, configuration and other characteristics. New product models can be added as the need arises.

An extension to STEP has been created to cover product information related to CNC machining. This is STEP NC. STEP NC forms the basis for the scenario that caught your attention at the beginning of this article. The development effort to make STEP NC product model data usable as direct machine tool input has already progressed substantially.

In May 2000, a prototype for the sets of data required to add machining information to the product model of a test part was demonstrated. A later phase of this project will develop the machine tool controller capable of accepting this "super model" as input. The current test part is a milled workpiece. Turning and grinding are on the horizon. The "super model" demonstrated in May used an emerging Internet language called XML to add information about machining strategy, tool path planning, and tool selection. XML makes the resulting database "Internet ready'—a key requirement for global e-manufacturing.

STEP Vs. IGES

To understand STEP NC and where it's headed, a look at STEP and its relationship to IGES is the place to begin. IGES was about exchanging data and only the data contained in graphics files. STEP is about sharing data, allowing parties to work together by communicating information interactively.

IGES had its start 20 years ago when designers and engineers were turning to computers to create product designs. Instead of drawing lines and segment of circles on paper to make graphic representations of what a product should look like, they started making those lines and arcs on a computer screen. The completed design could be saved as a digital file. Although creating the original design file might take longer than preparing the engineering drawing on paper, the design file could be quickly copied, modified, printed and otherwise manipulated. These time savings more than made up for the extra time it took to prepare. Moreover, the digital nature of the design file allowed it to contain much more information in a much more flexible format.

One big problem quickly emerged. The computer-aided design (CAD) systems used to create these digital design files were not compatible with each other. A design created on a Computervision system was meaningless to an Applicon system, for example. Companies with unlike CAD systems could not exchange CAD data.
The effort to resolve this situation got underway in the spring of 1980. Representatives of U.S. user groups, vendors and standards organizations began meeting regularly to create a neutral, non-proprietary database structure and data format for CAD files, dubbed the Initial Graphics Exchange Specification (IGES). In theory, CAD files translated into IGES could be exchanged with any CAD system that could translate IGES files into its own proprietary format.

Although IGES eventually became a workable, if imperfect, approach to exchanging CAD files, a major shortcoming with this approach became apparent right away. IGES allowed one system to communicate the lines and symbols of a computerized engineering drawing, but IGES failed to communicate the meaning of the information the drawing was intended to convey. It did not provide a reliable means by which product features could be transmitted with the geometry so that computer-based applications could "understand" the engineering drawing.

While IGES was being developed and gradually made more functional as it moved through the standards formation process, efforts to develop a true "product data exchange specification" were launched. The goal of this effort was to capture and convey "logical" information about product features and provide "physical" mechanisms for data exchange. Originally conceived as a U.S. initiative, this effort was soon seen as requiring international participation.

By 1984, this international effort to develop a Product Data Exchange Specification had been established under the auspices of ISO, the international standards making body. The goal was to define the methods for creating product data models that could be interpreted by computers. These models were intended to allow the exchange and sharing of product data in a way that the meaning of the data would not change throughout the product life cycle.

The international standards covering these product data models became known as STEP. For the last 15 years, various groups and committees (mostly comprising users rather than vendors) have been meeting regularly to develop standards for product data models. They have made considerable progress. Because the STEP standards are now sufficiently developed to cover all of the original purposes of IGES, IGES will receive no further development and refinement. STEP has officially taken its place.

By July 2000, every major and almost all minor CAD system vendors had STEP translators in the latest releases of their CAD products. Moreover, these translators have been tested for conformance and interoperability. With only a few exceptions did any of the translators fail to operate effectively. (Indeed, one of the innovative features of the STEP formation process was the early commitment to include testing procedures for assuring that STEP-compliant systems would truly function as intended. This provision may have slowed development but it appears to have paid off in the end.) In short, STEP is working. According to industry analysts, more than one million STEP enabled CAD stations are in place around the world.