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Digital Light: Millions of Pixels on the Road

For the past five years, development departments of Daimler, Automotive Lighting and Texas Instruments have been working on a high-resolution headlight principle. This new technology makes it possible to design the light distribution of headlamps more flexibly and more precisely than ever before. In addition, new lighting functions increase safety providing visual information for the driver in the front vicinity of the car. The first series vehicle with this system is the Mercedes-Maybach, which has been on the roads since mid-2018.

Digital Light Distribution

"Digital Light" is the name of this demanding and exciting development project at Mercedes. Better illumination, finer resolution of the recessed zones and additional guidance information for the driver are the tasks of the new lighting system. The light distribution of the headlamp is made more flexible and controlled fully automatically in a wide variety of traffic situations. First and foremost is the increase in safety when driving at night, but also improved driving comfort.

After fundamental preliminary investigations, it was decided at the beginning of 2014 to work with the development partner Automotive Lighting GmbH from Reutlingen on the so-called "Digital Mirror Device" technology (DMD) as part of the "Digital Light Processing" (DLP).

The Projector Principle

The DMD technology, available in simplified form in the "consumer" sector, for example in film projectors, has been further developed for the use in high-performance headlights. It is based on a matrix with a total of 1.3 million micro-mirror elements on a surface with a screen diagonal of 0.55". Each of these approximately 10 micron small mirror elements can be individually controlled electronically and is selectively moved back and forth between two positions. The matrix generated in this way is uniformly illuminated by high-current LEDs and projected onto the street within milliseconds by means of a multi-level lens system in the form of images. Each mirror thus generates a pixel of the projected image and can turn on, off or dim the pixel by its flip-over movement. Switching frequencies of a few hundred Hertz are used to modulate the image with 1.3 million pixels and create a video.

As part of the development work, this projection system with the micro mirror matrix had to be realized in a way that suited the automotive industry. All system elements had to meet the mechanical, electronical, chemical, thermal and optical criteria of automotive conditions and it had to be designed to meet the enormous demands of the car. Close cooperation between all parties involved in the value chain, from the developer of the microelectronic components to the lighting system developer and the automobile manufacturer, was necessary to get the product ready for series production.

New challenges for the electronics hardware and software

The development of this high-resolution lighting system also presented new challenges for electronics hardware and software development. For the hardware design for controlling the high-current LEDs and the 1.3 million micro-mirror elements, new technologies had to be used that had previously never been applied in the front lighting area.

For the first time, a dual microcontroller system has been integrated on a light module. Very powerful microcontrollers with graphics programming unit (GPU) and external Flash memory, which can withstand even the very high temperatures of up to 125°C, had to be found. The transmission of image and video data requires the use of high-speed video interfaces such as GMSL, OpenLDI or RGB888 with transmission bandwidths of >1 Gbit/s. For vehicle applications, these were previously known only in the field of infotainment. To successfully develop this system, it was necessary to build up the competence of graphics programming and video image generation even with computing power-limited embedded microcontroller systems. In these novel high-resolution lighting systems, the light functions and light distributions are no longer realized only via design of the lens systems and reflectors, but defined in particular by software algorithms. This creates completely new possibilities of dynamic light distribution during driving as well as projection of symbols depending on sensor and vehicle information.

Extended Lighting Functions

The high-resolution module serves all areas of lighting functions. It supports the low beam, e.g. in the dynamic cornering light through horizontal modulation and the high beam with additional intensity in the maximum and in the ADB light functions: If the main beam is not switched off even in oncoming traffic, it can be adapted in a very exact way thanks to its high resolution and it illuminates the surroundings of other vehicles precisely without dazzling their drivers. The high resolution ensures that conventional lighting functions can be significantly refined and improved, but also provides completely new lighting functions. Thus, in advance of the vehicle in a range of 12-30 m, the high-resolution DMD technology in the DLP modules, also called h-Digi, maps the "assistance projections" on the road supporting the driver at night.

In contrast to conventional systems, the light distributions with their maximums, their soft gradients of light distribution or their defined sharp edges for glare avoidance are no longer designed solely by the optical system. This task is now carried out by complex software solutions with corresponding calculation algorithms. They offer completely new freedoms to optimize the illumination in front of the vehicle and thereby improve the safety and comfort during night driving.

Multifunctional Mirror Matrix

In the spotlight, the h-Digi module, which has DMD technology, works together with additional light modules. The most important area in the center of the light distribution is accentuated by the digital module. For "background illumination" a larger 84-pixel matrix module with a three-line illumination field is used. The front-range and the side illumination are generated by three small basic light projectors, which are arranged one above the other in the headlight.

In the autumn of 2016, the first prototypes were presented during the "Mercedes Tech Night". A practical test convincingly demonstrated how the already introduced adaptive functions can be further improved and complemented in their performance by the new technology. It also showed how the novel lighting functions support the driver. The positive response from the global press was mainly related to the assistance projections in front of the vehicle, as shown in Figure 5.

Production Maturity with Mercedes-Maybach

At the Geneva Motor Show 2018, a vehicle with a DLP series headlights was presented to the public for the first time at the beginning of this year. The headlights of the Mercedes-Maybach are by far the most powerful matrix headlights on the market and support the driver in a wide range of driving situations.

Studies on such systems show that the driving behavior is positively influenced by these assistance functions. Thus, in tight construction sites, guide-line edges are automatically projected in front of the vehicle, marking the width of the vehicle and allowing the driver to maintain his own position on the lane in a relaxed but safe manner. They also provide the ability to better estimate the strip width relative to the vehicle width.

An optical warning (arrow) on the roadway also appears if there is a risk of unplanned swerving out of driver’s own lane. Furthermore, various warnings are given for a duration of about 3 seconds, for example in case of black ice, distance underruns or speeding. Warnings are projected directly in front of the vehicle. They are activated automatically after analysis by the vehicle sensors and according to the driving situation. The goal of the projections in the immediate vicinity of the driver's line of sight is to warn the driver effectively and without distraction. In a test series with test persons in real night traffic it could be shown that a projection that appears on the road as warning, e.g. if the permitted speed is exceeded, is perceived 60% more frequently than the same warning information presented via head-up display. The driver perceives the projections as most contrastive. The analysis of his/her reactions regarding braking behavior or accelerating, after the speed warning was projected, has shown a 60% more frequent reduction of speed, which positively influences traffic safety.

Summary

In conclusion, it can be stated that the digitalization of the headlamp represents a milestone in the further development of front lighting technology. If it succeeds in bringing this approach into as many different vehicles as possible, it can contribute to achieving the goal targeted by the Federal Government in the context of the "zero traffic deadline strategy". With the concept described above, the headlamp becomes a tri-functional system that adds smart automatic assistance to intelligently-controlled adaptive lighting functions and opens the option for further applications in automotive communication. Development of the second generation is already in progress to make this powerful technology available for other vehicle segments in just a few years.

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