Under Control

FASTER THAN REAL TIME

Most of us think of simulation as "merely" objective representation of things or processes. And they are. But bear in mind that language is also a kind of representation. "Natural language" - English, German, Chinese - is a map of the embedded belief of a culture. It contains one element of a game aimed at attaining some goal, be it getting work done or sharing a meal.

Computer languages such as Ladder, Drum and Paracell are all representations that reflect a particular "brand" of problem-solving. The same could be said of Lotus 1-2-3, HyperCard, or Windows. Natural language, computer language, and even commercial computer programs are all representations or simulations. The form of the representation is determined by its use.

Another type of simulation, of interest to manufacturers and engineers, allows modeling of chemical and other kinds of processes. Most simulations do not run on real-time basis, nor do they include direct sensory input from the process in question. A simulation tool frees engineers to tinker in a world of make-believe, to examine relationships between ingredients and play "what if" games. It allows them to methodically identify strategies for process optimization.

Computer-aided design (CAD) is simulation in the discrete manufacturing realm. Enhanced and virtual representations of the mechanical engineering world enable design optimization and concurrent engineering. Models can be used to examine relationships between objects for interference checking and allow structural, thermal, and other type analysis.

Narrow definitions for computer-aided design and simulation limit its application. A simulation must be a model of more than "just" a product or a process. Recently I visited Lockheed, where there is considerable interest in "space-age" composite materials. Controlling a composite's characteristics during its production can be difficult. And to get a handle on it, Lockheed has to be involved from the well head to the warrantee expiration. It wants to be able to "simulate" the entire life cycle of the composite material.

The design environment and associated system of today's simulation technologies are typically brittle, especially near the edge of the performance envelope of the software. Users either have to be experts in manipulating the platform or they have to bring in someone who is. But there is growing awareness that those who know the products and processes to be modeled must themselves be capable of manipulating the simulation.

Today there are three kinds of software; obsolete, OOPS, and rule-based systems. Two of the three hold within themselves the promise of user enablement-of increased productivity though advanced technology for more flexible manufacturing. OOPs (object-oriented programming systems) and rule based systems capabilities will be enhanced by direct coupling of the simulation to the "real" world. Real-time modeling is what will take process optimization to the next level.

Real time computing is fast, robust and predictable. And when modeling, the big question is always just how fast, how robust, and predictable do you want to be. Much like with a compact disk player for the home CD, the process must be over-sampled to make sure nothing is missed. The model must therefor be "faster than real time," and be able to anticipate how the modeled process will react, so that comparisons and projections are ready prior to an event's occurrence.

We know a incandescent light bulb lasts 1000 hours. So it should be replaced after 980hours. In the same way, we should be able to predict bearing failures in power turbines used to meet peak demand in power utilities. Predictive diagnostics are a powerful tool. But it's difficult to build a computer system capable of responding to what's going to happen tomorrow. To be real time, modeling systems must have the means to foresee developments.

A couple of other quick points. The mathematics used in most simulation packages assume linearity, for load as well as structure. This is a limitation. It may be that the use of standard operating systems such as DOS or UNIX hold back user enablement. Suppliers should examine the usefulness of a multi-user, object-oriented data base with n-dimensional representation.

Simulation and modeling technology today is at that level attained by aviation technology just after the Wright brothers arrived at Kitty Hawk. Someday, simulation capabilities will be comparable to the accomplishments of Boeing in the aerospace industry. Correctly used, we'll be able to see into the future.

As appeared in Manufacturing Systems Magazine May 1992 Page 58
http://www.manufacturingsystems.com




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