Electronics & Scientific Guide, Embedded Systems

Audi Matrix LED Headlight Technology

The light of automated or autonomous vehicles becomes digital. What this means and how digital light can be used to improve visibility and to optimize communication with the outside world is shown in this article by Audi.

Digital light helps. The fatal accident of the autonomous experimental vehicle of Uber at the beginning of this year has completely changed the opinion of experts on the need for outdoor lighting. So far, the prognosis was that a well-recognizable position light is entirely sufficient, since IR sensors, laser scanners and radar systems completely take over the detection of the outside world. The tragic accident shows how crucial high-quality lighting systems such as glare-free high beam are for today’s as well as for future road traffic.

Matrix LED light

A high matrix beam illuminates the road area in high beam quality, except for shadowing other road users to prevent glare. This illumination quality also improves the visibility of objects through a camera. In the Uber accident scenario, one can expect at least two seconds of gain in response time by matrix light, assuming a speed of 25 m / s and a minimum of 50 m visibility gain, although 100 m visibility gain and thus, in this case, four seconds somewhat realistic. Since software in the Matrix LED headlamp has replaced the previous mechanism for modulating the light distribution, this is a digital lighting system for vehicles.

Since the introduction of Matrix LED technology in 2013, there have been steady improvements in both performance and market acceptance. The Matrix LED technology also provides additional customer-oriented functions for different driving situations and visibility in other applications, such as rear lights and interior lights. Digitization will create new opportunities in the field of lighting that will further increase traffic safety.

Assuming the five levels of autonomous driving (Figure 1) with the optimal supporting light function, the result is a consistent recommendation for the use of Matrix LED headlights. At least in the evaluation or classification of objects in the video image matrix light is always advantageous for night driving. Other elements such as lane projections and status displays or even communication displays complement an optimal lighting configuration for autonomous or semi-autonomous vehicles.

Digital front lighting

Conventional communication between drivers and other road users, such as making eye contact, nodding or shaking hands, is merely impossible with autonomous driving. The lighting technology can offer two variants here as a substitute for the lack of communication – on the one hand in the form of projection systems that project information onto the road surface, on the other side in the way of high-intensity displays with a relatively low resolution for the display of symbols.

Projection systems: HD matrix light

Projection systems can be used both as HD matrix light (HD: High Density) and as a roadway projection system. An increase in the resolution of today’s matrix-LED headlight systems is based on the concept of a micromirror device (DMD) with high contrasts. In this DMD system, a reliable light source illuminates an array with a plurality of micromirrors; 1,000,000 pixels on a 0.55-inch chip are standard).

Each pixel is individually controlled so that high-resolution light distributions become possible. Each mirror has two stable states between which it can be switched back and forth. By quickly tilting the micromirror, all dimming levels can be set to the exact pixel. Depending on the quality of the sensor data, for example, it is possible to mask the exact vehicle contour of an oncoming vehicle or only the head of an oncoming driver, while the rest of the scenery is illuminated. However, the realization of this scenario fails because of the tolerance chain. Precision and reproducibility in the range of hundredths of a degree are not yet available from the moving vehicle today. In addition to these glare control systems, other assistance systems are also possible – for example, for marker lighting. Disadvantages of the DMD system are the high system complexity and the reduced efficiency since all pixels are always maximally illuminated and the “dark” tilted micromirrors direct the luminous flux into an absorber.

Projection Systems: Information Projection

Digital light can do even more: using high-resolution DMD headlights, symbols, graphics, auxiliary lines, directional arrows, etc. can be projected onto the road ahead of the vehicle. Above all, the zebra crossing projected by the vehicle is known, which, however, has only a meager chance of realization. The amount of light, angle and the distortion to be compensated from different viewing angles are contrary to the understanding. Also, it is not permissible to temporarily project valid traffic signs. These may only be erected by the road traffic authority or painted on the street – and this includes the so-called crosswalk.

Of course, the vehicle manufacturer must also very carefully consider what information better in the head-up display (HUD) are displayed and which are more useful on the road. In principle, it is possible to differentiate between information that makes sense only to the driver (HUD) and those that can warn or protect other road users (matrix projection). Information about your speed, valid traffic signs, Navi-arrows, turn-by-turn information and the ACC status are predestined for display in the HUD, while matrix projections are very well suited for warnings against black ice, obstacles or traffic jams as well as emergency braking.

Further developments also take place in the case of marker light and new functions to assist the driver in unclear situations. When driving on narrower road sections such as in construction sites, it could be difficult for the driver to survey the vehicle width exactly. A projected optical lane helps the driver to estimate the exact vehicle width. The system is also useful for winding roads: Here, the lines adapt to the route and show the driver the ideal driving line.

The system also facilitates driving on very narrow roads (for example, in Japanese residential areas), makes it easier for the driver to assess and can prevent dangerous situations at construction sites and bottlenecks.

Displays for communication

By communicating with the driver, pedestrians feel safer crossing a street. In contrast, the willingness of passers-by to cross the road is reduced when drivers are inattentive and do not make eye contact. Despite advances in automated driving, urban traffic management is still facing great difficulties, mainly because of a large number of road users and the need for communication. Motorized vehicles are likely to suffer the problem of mixed traffic with non-automated vehicles for decades to come, with pedestrians always playing an important role. Here, too, digital light can make a significant contribution.

In motorized vehicles, excellent communication between drivers and other road users is no longer possible. However, to maintain the trust between road users and automated vehicles, the connection between them remains crucial. For example, it makes sense to display or communicate vehicle condition and intention as well as pedestrian detection to establish a basis of trust.

Study subjects

To investigate what future vehicle-pedestrian communication can look like using appropriate symbols, which characters can be assigned to situations quickly and how intuitive they are, Audi conducted a subject study. In the run-up to the study, the participants selected both static and dynamic symbols, which were then evaluated by a panel of experts. From this, the symbols from Figure 3 were determined for the subject study.

For the characters of the vehicle-pedestrian interaction to be investigated were known symbols from the traffic as a template, for example, traffic light men, Kurvenleittafeln, no parking or driving direction, but also familiar icons from the vehicle interior such as icons of ACC and ultrasonic sensors or automatic start-stop feature and Symbols that can be displayed with LED strips. Also, a literature search was carried out. From these different signs were derived and symbols combined.

The study was carried out using two on-vehicle monitors that presented subjects with white symbols, aiming to test their intuition and correlation to situations, forming groups of understandable and ambiguous characters. With an intuitive query, the response times (minimum 2.72 s) and assignments (maximum 74%) of the symbols show only a low degree of intuitiveness. Also, the subjects prefer powerful symbols, especially for dynamic situations.

From the symbols shown, the STOP hand, the dynamic arrow (similar to the electric turn signal) and images of pedestrians with a vehicle cut off very well. Even with an intuitive query, the STOP hand shows the highest allocation ratio, with linear representations, such as bars, being misunderstood or not assignable at all. The next three best-ranked symbols (ranked 2 to 4) are about 57 percent of the vehicle with pedestrians and about 54 percent each of the animated turn-off arrow and the walker with the wave representation.

This clearly shows that it is already tricky with known characters to make an intuitively correct interpretation of the communication and that it is almost impossible with one-dimensional symbols. These icons are not very suitable for interacting with pedestrians. Particularly suitable are two-dimensional, possibly dynamic symbols such as symbol number 27 in Figure 3.

Digital light at the stern

In contrast to the front lighting, the rear lighting has the task to display necessary information such as vehicle width, brakes and direction indicator. In future applications, segmentation of the filament will also make it possible to generate different patterns or segment combinations, or to draw the driver’s attention to the activated function. Dynamic direction indicators provide meaningful evidence of how dynamic switching between segments of the light body can improve traffic safety and shorten viewing time.

Matrix OLED technology

The matrix OLED technology currently used in the Audi TT RS and the new Audi A8 is a promising approach on the way to the optimum matrix and display technology for rear lighting. Here, numerous advantages are combined: Compared to its passive LCD counterpart, the technology not only saves installation space but, as an active technology, is also more efficient. About luminance values of more than 1000 cd / m 2, this aspect is particularly important. Also, flexible solutions for future applications are possible.

For the autonomous vehicles of the future, dynamic signal functions, in particular, can play a decisive role in improving and ensuring road safety. A dynamic turn signal reduces the directional error rate and enhances driver decision-making by 0.6 s and 11.5 m at 70 km / h, respectively.

Other options include the customization of the tail light graphics – of course, in compliance with all international regulations and rules. Digital light offers many possibilities – even for autonomous driving.

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