QMT Features: July 2008
Nice body, fit car
PSA Peugeot Citroën quadruples scanning productivity with Metris ModelMaker  to ensure an accurate fit of car body assembly.

Europe’s second-largest carmaker has a history with digitalizing that dates back to 2001. Since then, PSA gained significant experience in applying laser scanning to digitize the geometry of vehicle body parts of prototype or early production vehicles.

“Dimensional accuracy is of prime importance in vehicle body assembly,” states PSA Poissy’s metrology department responsible. “During the assembly process of a trunk lid, for example, the geometry of the lid slightly changes due to the mechanical interaction between frame, glass, trim, lock, etc. When we prototype vehicle body parts, we closely monitor geometry using Metris MMD to ensure assembled body elements will fit perfectly. The use of a wide variety of materials – including composites and plastics – sets specific manufacturing and measurement challenges, and increases the need for reliable and efficient metrology solutions.”

 ESP enables the operator to scan a shiny logo as well as the dark base surface in one go.    The all-digital operation and wide laser stripe width of the Metris MMD scanner step up productivity.

Physically the largest part that PSA metrology engineers scan using the handheld Metris MMD is a body-in-white structure. Positioning the articulated measurement arm at one or two locations is sufficient to digitize a hood or the entire backside of a vehicle body, for example. Metrology engineers at PSA also use Metris MMD to scan interior trim parts, light units and various other parts. To deliver top data quality for different surface types even under difficult lighting conditions, the Metris MMD scanner features ESP (Enhances Sensor Performance).

ESP is an algorithm that automatically adapts camera and laser settings to accommodate varying surface shape, colour and reflectivity. This helps PSA engineers accurately deal with sheet metal, composites and plastics – without having to apply spray or other preparation measures. With a laser line that counts as many as 1028 measurement points, the scanner reliably digitizes freeform surfaces as well as the edges of individual features. Another reason why PSA opted for a non-contact scanning solution is the capability to reliably digitize softer trim material, eliminating the risk to scratch fragile components or press flexible parts. On finished cars, the system serves as an optical gauge for flush & gap inspection between body panels.

 The process of acquiring scan data to delivering optimized polygon mesh is managed by Metris KUBE. The obtained polygon mesh enables PSA metrology engineers to analyze geometric deviations.

Reducing scanning
When scanning a vehicle body part, a PSA engineer operates the laser scanner while the scanned surface takes shape in real time on the laptop screen. The displayed information provides instant feedback regarding scanning speed, coverage and progress. Scanning takes place at a relentless pace, thanks to the scanner’s extra large laser stripe and fast digital signal processing. “The result of the scan is a cloud of hundred thousands or even millions of measured surface points,” explains a PSA scanner user. “After filtering the point cloud to eliminate excess points, we generate a polygon surface mesh and optimize it, the entire process being smoothly managed by Metris KUBE. The tight integration between scanner software and hardware not only streamlines the scanning process, but also cuts the remaining post-processing effort in half compared to the previous scanning solution.”

According to PSA Poissy’s metrology department responsible, the metrology team represents a centralized unit that runs measurements at PSA sites across France to support vehicle development from prototype to release. “Regardless whether measurements are scheduled to take place in the PSA Poissy facilities, or at PSA sites in Rennes or Sochaux, for example, metrology engineers take the portable system with them and start scanning right away. This pragmatic approach offers maximum measurement flexibility and saves on logistics by reducing transportation of vehicle body (parts) to our metrology laboratory.”

 PSA applies laser scanning to verify the shape of lighting units and their positioning onto the body. Consistent body panel spacing and perfect-fit interior trim offer consumers a sense of quality.

Besides monitoring the geometric quality of vehicle body parts – Metris laser scanning forms an essential step in verifying numerical calculations PSA performs as part of virtual simulation. Metrology engineers at PSA systematically use the Metris MMD scanner to acquire digital 3D copies of structural components such as body frames, doors, windscreens and other parts. This touch with reality increases simulation accuracy and helps reduce the number of lengthy and costly physical prototype cycles. “Overall, when using the all-digital Metris laser scanner with wide laser stripe, we are able to complete scanning jobs four times faster than before,” says the PSA scanner user. “Productivity improvements of this degree enable us to take on additional metrology assignments and yet increase the level of data quality, all within the current capability of our metrology team.”


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