JUNE 2007
Is Time Travel Possible with History-based Modeling?
Looking for a Time Machine? Try History-based Modeling.
By John Wright McCullough, Kubotek USA
Remember Doctor Emmett Brown’s Flux Capacitor from the film Back to the Future? To jog your memory, Back to the Future was the top grossing U.S. film of 1985, coincidently the same year PTC released Pro/Engineer and Coca-Cola released New Coke. The popular second-term U.S. President Ronald Reagan actually referenced the film in his 1986 State of the Union address.
1.21 Gigawatt Flux Capacitor
In the film, the Flux Capacitor, mounted in a DeLorean DMC-12 driven at 88 MPH, made time travel possible for the young, acid-wash jeans-clad Marty McFly. Of course, the best scientists can offer at this time is that the possibility of time travel has not been ruled out, but it continues to be a popular plot for fiction.
Possibly the closest we will get to time travel for a while is the history-based approach to CAD modeling, which is the foundation of Pro/Engineer and has been adopted by most MCAD products in the industry. The promise of the history-based modeling approach is that after you have built a model once you can easily go back and change it. This is done by attempting to interface with a higher-level Historic Model made of precisely documented construction steps. The Historic Model is run through a playback engine to generate the required end result, a new geometric model.
The History-based Modeling Process
By altering the parameters, or adding or re-arranging the steps used in the original Historic Model an alternative Geometric Model can be output by the Playback Engine. When all the future changes that will be needed are well understood, a skilled history-based CAD operator can build a Historic Model that truly automates design iterations.
However, as Marty McFly found out in the film, altering history can be very dangerous. Upon arrival in 1955 Marty put his very existence at risk by accidentally disrupting the events of his parents courtship. Similar dependencies exist in complex Historic Models. Later steps in the Historic Model are often based on results from earlier steps. Numerous, difficult to track down errors in later steps can result from making a change that had not been fully planned into the original Historic Model.
In the challenging world of innovating new designs and solving new problems the changes to a model which will be needed in the future are usually not well understood before hand. The design engineer who authors the original Historic Model also can not predict the challenges of the downstream manufacturing engineer who will work with the model. As much as everyone would love to have a Flux Capacitor to get back to the beginning of a project and communicate what is known at the end, it is still not possible.
Kubotek’s answer to this conundrum is for engineers in challenging design situations with many unknown variables to abandon History-based Modeling. The alternative modeling approach on which KeyCreator is based is known as Direct Modeling (aka Dynamic Modeling). While the end result of changes using either process is a new precise 3D geometric model, the Direct Modeling approach does not store or use the original construction steps to facilitate editing.
The Direct Modeling Process
The fundamental difference between these two approaches is often difficult for engineers reviewing competitive CAD products to see. In the controlled and predictable environment of a prepared demonstration the history-based problems described here don’t show up. Once problems do start to appear the history-based vendor usually tells the customer they need more training in order to do a better job of putting the ‘design intent’ into the Historic Model. Engineers using history-based CAD have accepted that they frequently need to discard the original Historic Model and start the model over from scratch.
The Direct Modeling alternative to History-based Modeling is rapidly gaining acceptance in the MCAD press. Significant new innovations, technologies, and product announcements related to Direct Modeling are being introduced on a quarterly basis across the industry. It seems the era in which MCAD was dominated by History-based Modeling is ending. In potentially related news, Universal Studios Florida closed its attraction Back to the Future: The Ride on March 30, 2007. Flux Capacitors, however, are still available on eBay.
