STEINBICHLER COMET 5 robot-controlled, automated measurement
"Mit vielen Pixeln geht´s besser - Many pixels is best" - a photo-optical, three-dimensional measuring unit inspects the complete surface of car body parts in the press shop. Thus, quality control has become significantly more efficient.
Since July 2010, the quality control at BMW AG (press shop Regensburg, Germany / TR-30) uses an innovative measuring method (white light fringe projection). The conventional system which delivered only single measurement points of the object surface by using a touch probe, has now been replaced with this optical, non-contact technology for the dimensional control of car body parts. Dimensional accuracy is given if the actual dimensions of the part lies within the defined tolerances of a given nominal value.
"The advantage of the new measurement technology is that we are able to acquire more than a million of surface points of a sidewall frame within exactly the same measurement time - in comparison to only 500 points delivered by the former method! This gives us the possibility to detect even the smallest deviations on the complete object surface" explains Roland Vanino (TR-30), Quality Manager Measurement Technology, the benefits of the optical system.
How the white light fringe projection works: A number of light fringes in different brightness levels are projected onto the object surface. Using a digital camera with high pixel resolution, an image of the object is generated by the light fringes. Even the smallest dimensional curvatures and contour lines can be acquired with high accuracy (actual data) and can then be compared with the nominal data (CAD files).
The complete sensor system is mounted on an industry robot which moves it over the test part by PC program control. During the measurement of one car body part mounted on the clamping tool, a new part can be fixed on the opposite side. Thus, the cycle time has been significantly reduced. In addition, short transport routes between press line and measurement unit avoid waste of time.
Quality control in particular for new models: The dimensional control of car body parts directly coming from the press line is part of the quality control. Only if all parts are dimensionally accurate, they can be used without problems in body shop and assembly. "The decisive criterion for the dimensional evaluation of the body parts, is a minimal deviation within a tolerance in the decimillimeter range, e.g. recesses for tail-lights in the side frame", describes Vanino the necessary measurements.
Apart from the stamped parts in serial production, the main focus lies on new parts such as doors for the BMW1 and BMW3 successor models which are tested with the new optical system. "In the past, all new stamped parts had to be transported to Munich for initial sampling at the department for quality assessment. The initial sampling is now done at our plant in Regensburg, thus saving time and money", says Vanino.