Significant time savings thanks to a high-end testing system

An advanced photogrammetry inspection system allows for fast dimensional accuracy determinations for automotive fixtures and part carriers, as well as supporting handheld scanning performance

High-end photogrammetry designed for the shop floor and ideal for eMobility production

The Volkswagen plant in Zwickau has a history of more than one hundred years in car manufacturing. Founded in 1904 and 1909 respectively as the Horch and Audi plants, Volkswagen settled at this location in 1990. Initially, Volkswagen produced internal combustion vehicles in Zwickau, but in 2018 began converting to the production of electric cars, which began at the end of 2019 with the production of the VW ID.3.

The Zwickau vehicle plant is still home to the traditional production areas of body construction, paint shop and final vehicle assembly, but since 2020 only electric cars have been manufactured there. The approximately 10 700 employees at this Volkswagen site now produce fully electric vehicles such as the VW ID.3, ID.4 and ID.5, the Audi Q4 e-tron and the Seat Cupra Born, as well as the bodies for the Lamborghini Urus and the Bentley Bantayga.

The conversion of the plant into a multi-brand location for eMobility and the expansion of the variety of models produced demands more efficient work processes in the department of measurement technician Marc Gündel.

“Contrary to popular opinion, it has become rather more involved,” Gündel explains. “Due to the reduction of the vertical range of manufacture in the factory, much more complex assemblies are supplied today, which leads to a massively increased support effort. To cope with the extra work, we need the right measurement systems.”

In 2022, VW Zwickau acquired the DPA Industrial photogrammetry system from Hexagon. These measurement systems are equipped with only a single portable camera unit, making them the most portable metrology systems in the world. The DPA Industrial with its 50.6-megapixel industrial sensor is one of the high-end models from the DPA Series range of products. The C1 Camera unit is integrated into a robust housing with IP51- rated protection and is therefore particularly suitable for use directly in the production environment or in outdoor areas. Together with the DPA Pilot software platform, the system guarantees a complete high-productivity workflow, from signalling and recording to calculation and reporting, and with minimal training.

Fast and smooth inspection

“We use DPA Industrial as an inspection system for our fixtures,” explains Gündel. Before the system is used for the first time, all geometry fixtures are checked for dimensional accuracy with a laser tracker or measuring arm and corrected if necessary. Afterwards, a data recording is made with the DPA Industrial. For this, special adaptors are inserted into the reference bores and targets applied to the fixture. All relevant fixing points are signalled with uncoded marks.

“I’ll put it quite simply: we take a few pictures and can tell whether the fixture is OK or not OK.”

Marc Gündel

Fügemeisterbock, Analysen und Messtechnik

Volkswagen Sachsen GmbH, Zwickau

A kind of virtual template is created with the data generated during the measurement with the DPA system. If a problem is detected with a specific fixture, a comparison with this template can quickly determine whether the relevant fixing points have changed and how big any change is.

“We simply take a few pictures with the DPA Industrial and can make a quick statement as to whether the fixture is ok or not,” says Gündel. A quick check is important because many of the 300 to 400 geometric fixtures are integrated in protective circuits that must be interrupted for the check, which in turn means downtime in production. “That means the times we can use to check the fixtures are relatively limited. During normal working hours, these are the breaks. With the DPA Industrial, we only need 15 minutes for the inspection – a lunch break is enough to get a clear statement about a fixture. That prevents weekend work for us. Let’s say, it’s a win-win situation for both the company and the employees.”

It is not always easy to use measuring systems in the narrow environment of the manufacturing shop floor. Space is often confined and it can be difficult to find a suitable stand due to cable aisles or the vibrations of the production equipment. In this regard, the complete freedom of movement offered here by the handheld DPA Industrial is a huge benefit.

How digital photogrammetric analysis works

In the first step, the component is signalised with targets. Appropriate measuring adaptors are used to measure hidden points or elements, such as drill holes or edges.

Then the component is photographed from different directions with a handheld camera. It is important that the targets are in the measuring field and that there are overlaps between individual photos.

With the help of special photogrammetry software, the resulting images are processed either simultaneously with the data acquisition (online) or afterwards (offline) by a special photogrammetry software tool such as DPA Pilot. The software automatically calculates the 3D coordinates of all target points. The calculation is based on the principle of spatial triangulation of images and is fully automatic.

For uninterrupted production

“We also use the DPA Industrial to check our skids,” adds Gündel. Skids are part carriers that are used to bring the individual components to the processing station. To do this, the components are placed on the skids by robots, which then move them to the production line. At the VW plant in Zwickau, there are six identical skids for each assembly; in total, that makes 180 part carriers for all the vehicle models produced there. “We have to check the skids in exactly the same position as they remain in the production line. For this we have a special measuring table on which we can quickly perform checks.”

As with the fixtures, the skids are photogrammetrically recorded for this purpose before the first use. The resulting point cloud is used to create a virtual template that is later used for quick checking.

To keep the automated production lines running, the part carriers must be available at all times. “If a problem is reported to us with one of the skids, we need to be able to react immediately,” explains Gündel. “If, for example, a crash happens in the plant, the whole system comes to a stop, which means we have production downtime. That’s why time is a critical factor: with the DPA, we can carry out a quick check and determine in no time what damage has been done to the skid. With other measuring systems, this inspection takes three to four times longer.”

Referencing for scanning

The most important application for the DPA Industrial at VW Zwickau is currently its use as an add-on for a handheld scanner. “This is really phenomenal,” explains Gündel. “We signal distinctive alignment points and holes on the car body with targets, record them photogrammetrically with the DPA Industrial and export the captured points from DPA Pilot. We then import these points into the scanner software. Now we can easily scan in alignment with the car body using the handheld scanner. And that’s despite the fact that we can’t fix the body and it’s only on a loose trolley.”

The fact that they have managed to get these two independent systems – the DPA Industrial and the handheld scanner – to ‘talk’ to each other saves Gündel’s team the time-consuming task of sticking targets on the car body – “and the subsequent removal of the measuring marks,” Gündel adds.

The DPA Industrial has a decisive advantage when compared to the photogrammetry system offered with the scanner: “The DPA Industrial can also measure coded measuring marks and adaptors. This means that the DPA offers us many more possibilities for later applications.”

Gündel and his team are still in the early stages of using the DPA Industrial at VW Zwickau: “We are still in the discovery phase as far as possible applications are concerned. We have built ourselves up over the last 20 years so that we can measure everything. Now we want to make sure that we become faster.”

To do this, he and his team have been studying the topic intensively and trying to think ahead. “We now know how it works and are opening up new areas of application for ourselves. The possibilities offered by DPA Pilot, which we use as a plug-in for PolyWorks Inspector, with the coded marks and user-definable measurement adaptors, makes work easier and measurement even more efficient.”

In addition to the photogrammetry system, the measurement technicians at VW Zwickau also rely on laser trackers and portable measuring arms from Hexagon, among other measurement technology. “We have known some of Hexagon’s employees for 20 years,” says Gündel, who is very satisfied with his team’s long-standing cooperation with Hexagon. “It’s also beneficial for us to have such a cooperation. And I deliberately want to speak of cooperation here, because we have also further developed certain products together.”

With such a well-established and successful partnership, even more fruitful cooperation lies ahead for Hexagon and Volkswagen.

Figure 1. Before inspecting, the skid is signalised with scale bars, reference crosses and targets

Figure 2. After signalising, the skid is simply photographed from different directions with the hand-held C1 Camera

Figure 3. The C1 Camera is integrated into a robust industrial-grade casing that makes
it ideal for use on the shop floor, in the workshop or outdoors