Case Studies: Reverse Engineered Armor
As a provider of armored prestige vehicles, Carat-Duchatelet (Liège, Belgium) counts sheiks, kings, presidents, CEOs and other wealthy individuals among its customers. Currently, more than 40 heads-of-state from Africa, Europe, the Middle East, the Far East and the former Soviet Union are driven in Carat-Duchatelet vehicles. Besides integrating armoring into luxury vehicles, Carat-Duchatelet engineers and craftsmen stretch vehicles both in length and height, and create personalized luxury interiors. Today, the Belgian company is recognized as a leader in armor integration and the manufacture of specialty vehicles in the automotive industry.
At Carat-Duchatelet, 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 where reverse engineering comes into play.
Carat-Duchatelet engineers remove seats and trim, and scan the entire vehicle body using a K-Scan MMD from Metris (Brighton, MI). The geometric 3-D scan acquired by this portable metrology solution forms the basis for drastic vehicle modifications and detailed craftsmanship. The portable Metris K-Scan MMD enables them to ergonomically capture vehicle interior and exterior in one go.
“Using Metris K-Scan MMD, we scan the entire vehicle body, one time with the wooden parts attached and one time without,” says Eric Appelmans, research and development engineer at Carat-Duchatelet. “This approach allows us to accurately digitize the vehicle body and generate digital computer-aided design (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.”
Ergonomic, Efficient ScanningThe setup of the Metris K-Scan MMD system is fairly straightforward. The engineer positions the camera of the optical coordinate measuring machine (CMM) module next to the vehicle body. The three high-resolution, charge-coupled device (CCD) cameras of the optical CMM dynamically track the precise location and orientation of the handheld 3-D Metris MMD laser scanner.
“The absence of mechanical constraints creates a superior comfort level when scanning the surfaces of the body,” says Appelmans. “The scanner is equipped with a laser stripe of 100 millimeters, which enables us to acquire measurement points at a rate of tens of thousands per second. With Metris K-Scan MMD, we easily and consistently reach the required measurement accuracy of 100 microns. 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.”
When scanning is ongoing, it is important for the operator to see the point cloud being acquired on the laptop screen in real time. Metris Kube 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, Carat-Duchatelet 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 optical CMM’s unique dynamic reference feature. Three to six small LEDs applied to the car body and dynamically tracked by the optical CMM ensure that all movement is compensated accurately. Using this information, the K-Scan MMD system is able to dynamically relocate the laser scanner position, avoiding leapfrogging or part realignment altogether. K-Scan MMD additionally supports multiple standpoints for the optical CMM. Data acquired from different optical CMM locations refer to the same reference axes system and contribute to a single unified point cloud.
Streamlining Vehicle ModificationTo reduce the amount of measurement data, Carat-Duchatelet 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,” says 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 Appelmans, scanning with K-Scan MMD provides better insight in a shorter time frame compared to taking manual touch probe measurements using an articulated measurement arm. “K-Scan MMD 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. This enables us to design and develop all different vehicle modifications in the most effective way.”
Starting from CAD data, the research and development team of Carat-Duchatelet 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 the body, doors, hinges and windows, as well as the driveline transmission.
“The K-Scan MMD helps us a great deal in streamlining all our vehicle modification actions, providing top quality in the shortest time frame possible,” says Appelmans. “With accurate and complete CAD data, we minimize the risk for development surprises that may introduce expensive rework and process delay.”