Smart Camera Helps the Wheels Go ’Round and ’Round MACHINE VISION-BASED ASSEMBLY SYSTEM FITS AND MOUNTS WHEELS ONTO CARS IN CONTINUOUS OPERATION. Using manual assembly methods to mount wheels onto cars in continuous operation is extremely costly for automotive manufacturers. This is mainly because several assembly workers are required to perform the work. IBG Automation GmbH (Neuenrade, Germany), an automation solutions provider, has designed a sophisticated assembly system for the automotive industry that automatically fi ts and mounts wheels onto car bodies moving continuously along the line. This fl exible system can be used for a variety of vehicles and wheel types. By automating this process, automotive manufacturers not only see labor costs drastically reduced, but overall manufacturing quality improve as assembly errors are eliminated. Two six-axis Kuka industrial robots—one located on each side of a car body—gather wheel bolts and rims from their supply stations and screw them onto the car. The robots are synchronized with the conveyor and follow the car’s movement during assembly. Attached to each robot is specialized lighting with polarized and infrared fi lters. A Matrox Iris GT smart camera also is attached to each robot. The smart camera locates the rim’s center point and calculates its position (X, Y), rotation (Rz) of the bolt circle and distance to the camera (Z) in calibrated coordinates. Before these coordinates are given to the robot, the smart camera checks to see whether the rim design that it has located matches the rim that is expected to be given by the PLC. This last test prevents the wrong rim design from being mounted on the vehicle. Thirteen different wheel combinations— seven rim designs and four types of lacquer (white, silver, anthracite, and black)—are identifi ed. The entire automated wheel assembly process has a cycle time of only1 minute. SMART-CAMERA-BASED IMAGE PROCESSING The image processing system is based on the Matrox Iris GT smart camera. The application was developed with Matrox Design Assistant, an integrated development environment (IDE) that is bundled with the camera. The IDE lets users create machine vision applications by constructing a fl owchart instead of coding programs or scripts using languages like C++. Once development is fi nished, the project (or fl owchart) is uploaded and stored locally on the Matrox Iris GT. The project is then executed on the smart camera and monitored from the Web-based Human Machine Interface (HMI) running on a PC. A number of Design Assistant tools or fl owchart steps are used. Image acquisition and processing are triggered by a command from the network link, which contains information about the measurement job and the expected rim type. Several Model Finder steps are used to locate the wheel’s bolt circle and to verify the expected type of design. The Metrology step then calculates the rim’s position and orientation based on data provided by the Model Finder occurrences. A TCP/IP connection ensures communication between the smart cameras and the PLC. Results and images are logged to a shared network folder—using TextWriter and ImageWriter steps— and can be downloaded by remote maintenance staff for fault analysis. SOME CHALLENGES IBG is a longtime user of Matrox smart camera technology. Kai Kluwe, head of software development machine vision/measurement at IBG, explains, “Our experience with Matrox Iris smart cameras and its software has been very positive— we’ve deployed successful projects in the past using Design Assistant’s effi cient edge-based search tools.” IBG also is pleased with the level of technical support that was offered to them. In addition to the skilled local assistance that they received from Rauscher GmbH, Matrox Imaging’s master distributor in Germany, IBG took advantage of expertise available from Matrox Imaging’s Montrealbased, Vision Squad, a team of algorithm gurus who help customers assess application feasibility and determine how to best use Matrox software to solve application challenges. In this case, these challenges included IBG’s need to handle different design and color combinations along with overlapping rims resulting from their placement on the skid. A clever algorithm based on the Geometric Model Finder and Metrology steps was required to only use the indicative features belonging to the rim in the foreground while discarding those that belong to rims behind it. Other challenges included having different settings for image acquisition and Model Finder steps on each side of the assembly line and for each rim type, in addition to ensuring reliable depth measurement with a 2-D camera. “The Vision Squad provided an alternate and optimized method of using the metrology tool so that we were able to improve overall robustness,” explains Kluwe. DEPLOYMENT In summer 2009, the assembly system deployed at Magna Steyr (Graz, Austria) for the fi rst time—mounting wheels on BMW X3s. The assembly line was then modifi ed in summer 2010 to accommodate the different rim designs for the new Mini Countryman. This modifi cation required extensive customization in the Design Assistant project. In March 2011, IBG collaborated with Rauscher GmbH and Matrox Imaging’s Vision Squad to rework the locating algorithm, which resulted in signifi cant improvements in cycle time. Throughout the entire process, IBG has taken advantage of the enhanced features and functionality offered in the newer version of Design Assistant software. This Matrox Iris smart-camerabased inspection system is currently deployed on one production line at Magna Steyr to automatically mount wheels onto continuously moving vehicle bodies, and at Volkswagen (Emden, Germany), two more production lines use the system in wheel supply stations to detect the rotation of the wheel’s bolt circle. Volkswagen’s fi rst system has been in operation since 2009 with an availability of 99.9%. Due to that system’s success, Volkswagen commissioned IBG to install a system on their second production line at the beginning of 2010. benefits By automating the process, automotive manufacturers not only see labor costs drastically reduced, but overall manufacturing quality improve as assembly errors are eliminated. The smart camera locates the rim¡¦s center point and calculates its position (X, Y), rotation (Rz) of the bolt circle and distance to the camera (Z) in calibrated coordinates. An algorithm based on the Geometric Model Finder and Metrology steps was required to only use the indicative features belonging to the rim in the foreground while discarding those that belong to rims behind it.
Published by QualityMagazine. View All Articles.
This page can be found at http://digital.bnpmedia.com/article/Case+Study/823812/80255/article.html.