COAT OF ARMOR

As the world leader in armored prestige vehicles, CARAT-Duchatelet (Liège, Belgium) counts sheiks, kings, presidents, CEOs and other wealthy VIPs among its customers.

This Belgian company is recognized as the world leader in armor integration and the manufacture of specialty vehicles in the automotive industry. Far away from mass and series production, CARAT-Duchatelet integrates the highest level of security and luxury into prestige sedans, limousines and off-road vehicles. Currently, over 40 heads-of-state from Africa, Europe, Middle East, Far East and the former Soviet Republics are driven in CARAT-Duchatelet vehicles.

Next to integrating armoring into VIP vehicles, engineers and craftsmen stretch these vehicles in both length and height, and create personalized luxury interiors. The armor development and integration process starts with crafting armor component shapes in wood. As wood is easy to manipulate, engineers quickly gain a rough idea of how new armoring will fit into a particular vehicle brand or type. This is the point where reverse engineering comes into play.

Before stretching and armoring luxury vehicles, engineers remove the seats and trim, and scan the entire vehicle body by using a Metris K-Scan MMD. The geometric 3D scan acquired by this portable metrology solution forms the basis for drastic vehicle modifications and detailed craftsmanship. This portable unit enables them to ergonomically capture vehicle interior and exterior in one go.

"Using the K-Scan MMD, we scan the entire vehicle body, one time with the wooden parts attached and one time without," says Eric Appelmans, an R&D engineer at CARAT-Duchatelet in Liège. "This approach allows us to accurately digitize the vehicle body and generate digital CAD information. Detailed CAD data provides the insight we need to create some sort of invisible bullet-tight cage by optimizing the design of steel plate and glass armor parts."

The setup of this inspection system is fairly straightforward. The engineer positions the camera of the Optical CMM module next to the vehicle body. The three high-resolution CCD cameras of the Optical CMM dynamically track the precise location and orientation of the handheld 3D laser scanner. "The absence of mechanical constraints creates a superior comfort level when scanning the surfaces of the body," explains Appelmans. "The scanner is equipped with a laser stripe of 100 mm, which enables us to acquire measurement points at a rate of tens of thousands per second. With this system, we easily and consistently reach the required measurement accuracy of 100 micron. But most important for us is the ergonomic handgrip of the scanner and the unmatched ease-of-use delivered by the system's optical CMM technology."

While the scanning is an ongoing process, it is important for the user to see the point cloud being acquired as it develops on the laptop screen in real time. The system's software manages the captured point cloud of the vehicle body, which typically consists of hundreds of thousands or even millions of accurate measurement points.

To conveniently access all locations inside the car body, engineers carefully select optical CMM positions that provide optimum coverage of the scan area. To compensate for any vehicle movement during measurement, the operator applies the CMM's unique dynamic reference feature. Three to six small LEDs are stuck to the car body and dynamically tracked by the CMM ensure that all movement is compensated accurately.

Using this information, the inspection system is able to dynamically relocate the laser scanner position, avoiding leap frogging or part re-alignment altogether. The system additionally supports multiple standpoints for the CMM. Data acquired from different CMM locations refer to the same reference axes system and contribute to a single unified point cloud.

To reduce the amount of measurement data, engineers apply curvature-based filtering algorithms to eliminate obsolete measurement data in flat plane surface areas. "After point filtering, we export the point cloud in IGES or ASCII format, and import the file in CATIA V5 software," explains Appelmans. "On the basis of the point cloud data, we create a surface mesh and generate CAD surfaces. For us, the process of fitting freeform CAD surfaces through measurement points represents a largely automatic procedure. Only for particular edges and roundings that are deemed critical, we manually fit surfaces and select the optimum level of smoothening. This kind of flexibility enables us to take control of the CAD generation process and obtain high CAD definition quality."

According to Appelmans, scanning this system provides better insight in a shorter time frame compared to taking manual touch probe measurements using an articulated measurement arm. "This inspection system offers a comfort level and data acquisition rate that are simply beyond comparison. Our approach of digitizing a complete car in one go at the start of the project avoids many costly and time-consuming iterations later on the process. This enables us to design and develop all different vehicle modifications in the most effective way."

Starting from the CAD data they generated, the R&D team specifies detailed requirements for steel and glass armoring and interior design. For radical vehicle modifications ? such as vehicle extension and raised roof ? a pre-scan may be executed to design adaptations to body, doors, hinges and windows, and driveline transmission. "The system helps us a great deal in streamlining all our vehicle modification actions, providing top quality in the shortest time frame possible," notes Appelman. "With accurate and complete CAD data, we minimize the risk for development surprises that may introduce expensive rework and process delay."

CARAT-Duchatelet, Rue Winston Churchill 413, B-4020 Liège, Belgium, +32 4349 55 55, Fax: +32 4343 84 29, www.carat-duchatelet.be.

Metris, 1577 Star Batt Drive, Rochester Hills, MI 48309, 248-853-6907, Fax: 248-853-6945, www.metris.com.