STEINBICHLER COMET 5
Audi AG in Ingolstadt, Germany
MODULAR FLEXIBLE REFERENCES
ROBOT-CONTROLLED SYSTEM MEASURES PROTOTYPE PARTS
Time and accuracy are essential in checking the dimensions of prototype parts, such as doors, hoods and trunk lids. At Audi AG in Ingolstadt, Germany, this challenge is met using a robot-assisted 3D digitizing system from Steinbichler Optotechnik, Neubeuern. The results delivered by the system help the car manufacturer optimize the manufacturing process.
When developing a new car model in the automotive industry, a number of concept cars and prototypes need to be built quickly and with high precision in the pre-production stage. The time and accuracy with which the individual parts are measured and evaluated play a key role at this stage, particularly since the parts also undergo changes during the development process. Klaus-Peter Erben, the head of the bodywork prototype department at Audi's Pre-Production Center in Ingolstadt, Germany, and his successor Dr. Friedrich Burgahn were therefore looking for a measurement solution to efficiently and sustainably monitor the production of formed sheet metal parts. As a result, the benchmark for selecting a suitable measurement solution was set very high. The system was to allow measuring the parts without prior preparation, while at the same time using optical metrology to measure the parts directly at the position of installation in the car.
Audi's requirements specifications also included the following parameters:
- Digitizing of a part within ten minutes
- Automatic evaluation of edges/boundaries and mounting holes in the part
- No need to provide reference marks on the part before measuring
- Fully automated measurement evaluation (process fully automated through to report generation)
- Output of the measured data in STL data format; other departments must be able to access the data for analyses
- Minimization of the number of measurements (no stock holding, reproducibility of equipment ensured)
- Evaluation of the measurements with an accuracy of 0.2 mm for surface edges and object edges (circles, oblong holes, edges/boundaries, etc.)
- Seamless data exchange with other systems.
Audi's new quality assurance procedure is aimed at optimizing their production processes in the pre-production stage. Another objective is to provide access to the digital product data and the associated logs and reports from the pre-production stage in all subsequent production stages.
After selecting and comparing different solution approaches from different suppliers, and on completion of a test phase, the decision-makers at Audi chose a robot-assisted 3D digitizing system from Steinbichler Optotechnik, Neubeuern (Fig. 1). The solution consists of the COMET 5 4M digitizing system, a Kuka KR 150 standard industrial robot with arm extension, a VKR-C2 control unit, and two motorized rotary tables controlled by a PLC. The COMET 5 4M white light fringe projection system is combined with specially developed modular flexible references, meeting Audi's requirements on time frame, accuracy and operational concept. This patent pending concept of modular flexible references eliminates the need for a higher-level measuring system, which would have led to drawbacks when measuring parts in different positions. Another point in favor of the solution is that it does not use the conventional photogrammetry method – and that saves time. The 3D sensor is implemented as the robot's sixth axis. The two rotary tables can be used alternately to perform a measurement on one unit while preparing the next part on the other unit. This considerably reduces system idle times.
A specially developed clamping concept allows measuring the parts from both the front and rear. This is achieved by setting up octagonal, bar-shaped reference elements around the part in any desired configuration. The reference elements are provided with coded measurement markers. The key advantage of this method is that all the reference elements supplied have already been photogrammatically calibrated at Steinbichler and are permanently stored in the system as reference data. During a measurement, the system transforms and matches the individual data sets to the available point lists. The reference elements can be individually configured for each part and also combined with one another with only minimum changes to the measurement program. This way, users only need very few measurement accessories. The necessary computing power and performance is provided by two Windows XP 64-Bit industrial PCs – one PC for data acquisition and one for data processing and analysis.