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STEP-NC is an advancement still searching for its markets.

You could say that NC code (RS274D) is the devil that most manufacturers have learned to live with when it comes to working with CNC machine tools.

Though NC code has a base structure, each make, model, and configuration of machine tool potentially introduces its own subtle nuances. To fully utilize the machine tool's full set of capabilities, each of its unique codes needs to be supported. Some classes of machines are simple enough to be programmed by hand; the programmer writes complete programs specifying tool changes and coolant control, as well as performs the necessary mathematical calculations to determine the coordinates of the move to, go-to commands. But the complexity of machine tools and parts being machined is making hand programming more and more impractical, if not down right impossible.

As a result of this ever increasing complexity, CAM systems are being used more and more commonly to create programs for CNC machine tools. It has fallen onto the CAM systems' post processors to generate the appropriate NC code for the targeted machine tool. Creating a post processor to output good NC code is not necessarily an easy or straightforward task, particularly when dealing with advanced machine tools. It is not uncommon to have to maintain vast libraries of post processors to support the machine tools within a manufacturing facility. Even when good NC code is generated by a CAM system, the amount of process information that is lost severely diminishes the level of functionality that can be supported down at the machine tool's controller.

It was because of this incredible overhead to manufacturing--introduced by post-processing, machine-specific NC code along with the minimized data content of conventional NC code--that the International Standards Organization (ISO) initiated an activity to define the next-generation NC exchange format, or STEP-NC.

At this point, STEP-NC is on the verge of being declared a Draft International Standard (DIS), just a step away from receiving its full International Standard (IS) status. Usually, when a STEP standard receives DIS status it begins to receive attention from vendors, which begin to implement support for it. At this point, it is unclear just how quickly STEP-NC will be put into use after it has received DIS status and possibly even IS status.

The background

STEP-NC, also referred to as AP238 in the ISO standards community, is intended to replace RS274D and all its proprietary dialects. Moreover, it is expected to provide the data foundation for next-generation intelligent machine tools.

Because of its ties to ISO, STEP-NC has been an international activity, with different project teams around the world focusing on different types of machining. In the United States, the STEP-NC effort, led by STEP Tools, Troy, NY, has focused primarily on two- through three-axis milling, with an eye to five-axis milling.

Initially funded through an Advanced Technology Program grant from the National Institute of Standards and Technology, STEP Tools has over the past four years overseen the development of a number of STEP-NC prototypes, which were then used to demonstrate the potential and viability of the STEP-NC format and the technologies it enabled.

It was through these prototyping projects that the original concept envisioned for STEP-NC evolved to a more practical definition. In its original concept, STEP-NC captured all the part data and process information required to create a part, and the STEP-NC-enabled controller was expected to generate the toolpath. The explicit toolpath was a by-product used only to statically document the toolpath generated by the controller. In this way, the STEP-NC file was transferable between various machine tools because each machine tool was responsible for generating its own toolpath, given the information contained in the STEP-NC file.

Automatically generating toolpath turned out to be a fairly daunting requirement for supporting STEP-NC, so STEP-NC's notion of explicit toolpath was revisited. It was decided that rather than defining explicit toolpath in the STEP-NC as a by-product, the STEP-NC file would embrace explicit toolpath as a fundamental data structure. As a result, STEP-NC became more an evolutionary change from the current RS274D format than a revolutionary change. All of a sudden, STEP-NC was transformed into a more practical approach.

Based on this new orientation using explicit toolpath, a series of conformance classes, which define subsections of the standard to allow partial support (and reduced implementation cost) were defined for STEP-NC. The conformance classes defined for STEP-NC were:

CC 1--explicit toolpath geometry

CC2--part geometry (B-Rep solid)

CC3--feature and operation data

CC4--design specification data (dimensions and tolerances)

Like other STEP standardization activities, STEP-NC is following a structured approach to defining the data format, though it has greatly benefited from the various prototypes developed so far.

The influencers

A DIS declaration draws closer, but STEP-NC's adoption in industry really depends on how a number of different industrial communities--CAD and CAM software vendors, machine tool vendors, and end users--respond to STEP-NC. And like the tumblers on a lock, each of these communities needs to fall in line for STEP-NC to play a role in manufacturing. Each of these communities has different concerns and different hurdles to overcome before it can adopt the new standard.

End-users in manufacturing are fairly predictable. These are the folks who subscribe day-in and day-out with the motto "If it isn't broken, don't fix it!" With good reason. They've got systems in place that, though probably not perfect, work well enough; and they use them to get the job done. Introducing a new technology, even if it displaces a less desirable one, is not necessarily a straightforward decision. In addition to figuring out how to transition from their legacy environment, they need to look at the overall picture to determine what potential risks will be introduced versus the gains that could be potentially made. If the gain is only a slight increment and the risk is great, in all likelihood the change won't be made. On the other hand, if the gain is great and the risk is slight, then there is a greater incentive to change. Unfortunately, when it comes to STEP-NC, it's really too early to have more than a glimmer of gain, and the risks are primarily related to STEP-NC's adoption by vendors.

Machine tool vendors rely upon being able to differentiate their products from other machine tool vendors' products. Part of that differentiation depends on the unique functionality they can incorporate into their machine tools. That unique functionality often requires NC code specific to that particular machine tool configuration. A standard NC code such as STEP-NC levels the playing field by providing a common input across all machine tools. The STEP-NC file that runs on the high-end machine tool from one vendor will potentially run on a machine tool from another vendor. Differentiation becomes more difficult. Of course, what machine tool vendors produce can be influenced by what end users are asking to buy. Unfortunately, most buyers aren't in the market for a machine tool that operates off STEP-NC, even if one exists, because currently there isn't an easy way to generate a STEP-NC file for it.

For the most part, CAM software vendors are focusing their resources on improving the functionality of their applications, expanding capabilities to support more styles of manufacturing or other market segments. They are driven by market demand and market opportunity. They recognize a good opportunity when they see one.

A recent example of responding to the market was when CAM vendors recognized the opportunity with multi-task machining and created versions of their software to support multi-tasking machine tools. Unfortunately, though post processing continues to be a critical aspect of CAM, with considerable overhead for many CAM vendors, the opportunity for STEP-NC hasn't materialized yet. Certainly the lack of machine tools that operate off STEP-NC is a key contributing factor. On the technical side, CAM systems will also need to be re-engineered to support the full range of STEP-NC as a number of data elements are not readily supported in CAM today. And part of this re-engineering is dependent on the quality of information provided to CAM systems from CAD systems as the STEP-NC file contains a more complete product specification.

Therein lies the final hurdle--CAD systems providing a complete, computer-interpretable product data model with geometry and product specifications (such as dimensions and tolerances) that could be used to drive manufacturing applications. Today, most CAD systems do geometric modeling, creating a nominal part model. But the product data, or specifications, are usually handled by a drafting subsystem whose data are neither stored as part of the core product model nor encoded in a way that is readily computer-interpretable.

To realize the full promise of STEP-NC. the design-to-manufacturing pipeline needs to be operating from product data models. CAD vendors are gradually beginning to fully appreciate the value of product data models and are evolving their geometric modeling systems into product modeling systems, but the evolution is still not complete or widespread.

If this all sounds a little Catch-22, maybe it's because in many ways it is. Though STEP-NC holds a lot of promise for the manufacturing industry by significantly advancing the quality of information made available to machine tools, an approach still needs to be developed that successfully introduces STEP-NC into the market.

If that finally occurs, what a fantastic coming out party it will be. Until then, STEP-NC runs the risk of being all DIS'ed up with no place to go. Gibbs and Associates,

John Callen

Vice President-Marketing

Gibbs and Associates

John Callen, vice president of marketing at Gibbs and Associates, has been a strong advocate of STEP-NC since participating on the Model-Driven Intelligent Control of Manufacturing program's Industrial Review Board. His current STEP-NC involvement has branched out into other next-generation manufacturing technology programs such as Open Modular Architecture Controller, Smart Machine Platform Initiative, and Next Generation Manufacturing Technology Initiative.
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Title Annotation:machine controls
Author:Callen, John
Publication:Tooling & Production
Date:Dec 1, 2005
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