Nowadays, hardly any vehicle manufacturer does without an integrated head-up display (HUD) in new models. And for good reason: the new systems have been proven to increase road safety and are regarded as pioneering. However, HUDs also come with a number of challenges that can have a disruptive effect on driving performance. For example, the indicators can be difficult to read in strong sunlight or poor illumination, while incorrect settings can even dazzle or significantly distract the driver. Comprehensive test series are required to rule out such problems in advance. OEMs must either rely on the results from suppliers or invest heavily in their own test benches. Many existing test benches on the market use old measurement methods. Their accuracy and measurement diversity no longer meet the requirements of new technological developments, which is why lengthy comparative measurements are required. In collaboration with the test bench specialist GEFASOFT, ARRK Engineering has therefore developed a new high-precision HUD test bench, onto which the entire windshield can be clamped. This means that even pioneering HUD technologies, which are increasingly being developed by OEMs, can be measured. Regardless of the manufacturer, various optical properties can be recorded fully automatically and much more precisely than ever before with a high degree of repeatability, as confirmed by a measurement capability test.

When the industry gathered at the IAA Mobility in Munich in 2023, augmented reality head-up displays (AR HUD) were one of the hot topics. In contrast to just a few years ago, HUDs are no longer considered a cost-intensive “gimmick”, but have become an integral part of the driver assistance systems of new vehicle models or, for some manufacturers, will even be the main display system in vehicles in the future. By displaying relevant information such as speed and navigation as well as warnings and infotainment directly in the driver’s field of vision, they need to take their eyes off the road less often. In the case of future-oriented AR HUDs, it is no longer just static information that is projected directly onto the road from the driver’s perspective, but also contact-analog information. In this way, ADAS (Advanced Driver Assistance Systems) such as distance and lane-keeping assistants can respond dynamically to what is happening in traffic and, for instance, immediately display potential sources of danger. Compared to classic head-down displays such as an analog or digital instrument panel with static information, this increases driving safety in two ways.

“HUDs are like any other technology: the more functionalities are mapped, the greater the demands on testing,” says Sebastian Hensle, Group Manager Optical Systems at ARRK Engineering. “Especially in the context of new, larger HUDs or display content that is projected in the so-called black area of the windshield, for example, it is necessary to measure the entire windshield, which our previous test bench was simply unable to do.” In turn, windshield test benches already available on the market were not able to demonstrate the high measurement accuracy required by OEMs for complex HUD systems. A test bench that could meet the strict specifications for full-surface measurement first had to be designed. In search of a development partner for this mammoth project, ARRK Engineering turned to automation specialist GEFASOFT in 2020.

Flexibly customizable and expandable for new HUD generations

“We chose GEFASOFT as our project partner for two main reasons,” explains Hensle. “Firstly, because of their many years of expertise in the windshield and HUD sector and, secondly, because we were able to obtain hardware and software from a single provider.” This complete package ensured that all software-hardware interfaces are working perfectly and that the test bench meets the specifications defined by ARRK Engineering in terms of both hardware and software. Conventional windshield test benches are not up to this challenge, as they usually have to meet less stringent requirements. “We had to modify our software accordingly in order to realize the required test scope and measurement sequences,” confirms Jonathan Guthmann, Project Manager Vision/HUD at GEFASOFT. “We also equipped the system with comprehensive access options and interfaces for our own extensions, so that our colleagues at ARRK Engineering can keep it state of the art in the future and adapt it to the challenges of new HUD generations.”

The second major requirement was the flexible design of the test stand. In order to improve the workflow when inserting a new HUD projector, GEFASOFT designed an automated conveyor line for moving the projector from the change position to the test position. In addition, the so-called windshield master (windshield cut-out usually made of stainless steel), which imitates the topology of the windshield for the test purpose, can be moved into a safe changing position and replaced in a few simple steps. “The windshield itself is also becoming increasingly important as part of the overall HUD system,” explains Hensle. “That’s why we designed the new test bench on the basis of a windshield test bench.” As an alternative to the windshield master, it is also possible to place the entire windshield for testing – regardless of manufacturer or vehicle type. “This will become very relevant for future 3D or AR HUDs, as ever larger areas of the windshield will be used as a contact-analogue projection surface,” adds project manager Alexander Düring, GEFASOFT.

Investing into the future: test bench measures 5 times more precisely than required

For the two-dimensional photometric measurements, an LMK 6 color camera from TechnoTeam was installed. It not only has a high-resolution sensor, but has also been equipped with a lens that features a large field of view (FOV) for this purpose, complementing the standard setup for distortion measurement. “We originally wanted to use a measuring robot to guide the camera,” recounts Hensle. “However, its articulated arms were not able to meet the strict specifications for the measurement tolerances.” The camera is therefore now guided by a linear system, which achieves a positioning inaccuracy of less than a tenth in all camera positions with a maximum travel distance. In addition, high priority was given to the mechanical stability of the test bench, which weighs around 3.5 tons. As a result, such high measurement and repeatability accuracy can be achieved in the series testing of HUD projectors that the measurement capability limits specified by the OEMs are undercut by a factor of five, as has been proven in relevant test series.

Thanks to the optimized alignment of hardware and software by GEFASOFT, the high-precision measurement, including the documentation and traceability of the results, is fully automated and does not need to be monitored manually. It is therefore no longer an issue to run longer tasks such as luminance measurements, which can easily take three to four hours, simply overnight. “In GEFASOFT, we have gained an experienced project partner who was able to reliably realize our ideas of a highly automated yet flexibly expandable HUD test bench. We are now prepared for new generations of HUDs – be it AR HUDs, which were presented by OEMs at the IAA, or future technologies, for which the testing of the windshield as part of the complex overall system will become increasingly relevant,” concludes Hensle.

Further information at https://www.gefasoft.com/ and https://engineering.arrk.com/