Vehicle Measurements Performed at Speed of Light

The Volkswagen Commercial Vehicles factory in Września, Poland represents the most cutting-edge production facility in the entire VW Group. Werner Steinert, the Quality Manager, was tasked with acquiring measuring technology as impressive as the production facility itself. He opted to fully leverage the potential of optical measuring technology.

To ensure that even difficult-to-reach characteristics on the car body parts are inspected perfectly, six axis robots with a large range of motion are used. Due to the compact design of the Zeiss AIMax sensor (height: 155 mm, width: 134 mm, length: 125 mm), even those characteristics in narrow or difficult to-reach areas on the car body can be inspected. “This makes the ZEISS AIMax so well-suited for in-line inspection,“ says Steinert.

The combination of three measuring principles in a single sensor – multi-line triangulation, gray-scale image processing and shadow analysis – is another plus for vehicle body manufacturing. These three measuring principles make it possible for the ZEISS system to measure complex geometric characteristics including special boreholes, holes, screw threads, weld nuts, gaps and flush. “Welded studs, and we have a lot of those, can only be measured in-line with the ZEISS AIMax,“ says Steinert, who was already familiar with the ZEISS system from a VW plant in Russia. The digital camera technology with high resolution and flexible illumination control for optimum lighting in every situation ensures ideal contrasting of the evaluated features. For example: nuts found under sheet metal are clearly visible. “Due to the adaptive illumination, it is possible to measure diverse materials,“ says Steinert. “And that‘s a major plus.“

Measurements are performed at lightning speed. The typical measuring time with the ZEISS AIMax, including robot movement, is 1.8 to 3.0 seconds per measuring position. “This speed allows us to inspect a lot of characteristics on a vehicle body parts within the demanded cycle time helping enormously with process optimization.”  

Performing 100% Inspection
For a vehicle to roll off the production line every 3.5 minutes requires the in-line measuring technology to operate in sync with the stipulated timing in production. In addition to the ZEISS AIMax sensors‘ very high level of basic accuracy, Steinert was also impressed by the speed of the system offered by Carl Zeiss Industrielle Messtechnik GmbH. “We wanted the best robot-based 3D in-line measuring technology on the market,“ says the Quality Manager, who has been working for VW for 25 years. “There was something else that made ZEISS the right choice: “We wanted a partner that has skilled employees who could work under extreme time pressure,“ says Steinert. “It was already clear after the first few weeks of production that the in-line approach was the way to go.“ All five stations work perfectly.

Every vehicle body part – from the undercarriage to the side panels – passes through the corresponding in-line measuring station. The undercarriages for the different models vary the most, and for this part between 82 and 122 measurement points are inspected to ensure the stipulated tolerance specifications have been met. To help the entire measurement process run smoothly, a RFID chip on the undercarriage transfers the information necessary for selecting the right measuring program to the in-line station. As soon as the undercarriage is in position, the software already knows what subprogram should be run to control the four measuring robots – no human intervention is necessary. Programmers have already defined when a particular characteristic needs to be inspected and which ZEISS AIMax sensors should be used.

The sensors regularly calibrated by measuring spheres installed within the cell from three different positions. The captured data is used to continually recalibrate the measuring system. This process is necessary to ensure a high level of precision during the measuring process. If the software did not account for the heat emitted by the robot arm motors, the entire system would be adversely affected.

Keeping an eye on the entire production line
All car body parts are inspected. “This way we know immediately where we need to modify our processes,“ says Steinert.  For Quality Assurance employees, monitoring the in-line stations is straightforward. The monitor at each station shows them how close specific characteristics are to exceeding tolerance. “We start paying very close attention once tolerance utilization hits 75%,“ says Steinert. Employees check how the values have changed on a daily basis or even after each shift. Stopping the production line because of exceeded tolerances is a situation to be avoided at all costs. Often the engineers from the Quality Assurance department can already identify the cause of tolerance deviations by examining the photographs taken by the camera on the ZEISS sensor for the particular characteristics and which are saved as needed. “This makes it easy for us to determine if there is something like glue in the boreholes,“ says Steinert. This is just a simple example of how the data acquired from the in-line stations helps the quality managers at VW improve the manufacturing processes at the plant. “We just send the photo to the employee responsible and they optimize the application of glue, which eliminates the need to rework the part later,“ says Steinert.

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