The sensor-integrated headlight for driver assistance systems is in development at the Smart Headlight project at the Fraunhofer Institute in Germany, which has already submitted a patent application.
Self-driving vehicles need a wide range of sensors to pick up on potential hazards in the same way that human drivers do. As the number of sensors increases, so too does the amount of space required to fit them – something that is often incompatible with a designer’s vision.
The Fraunhofer team has discovered a way to integrate certain sensors discreetly, the research organisation said. By combining optical light, radar, and lidar (Light Detection and Ranging) in the headlights, the researchers hope to improve sensors’ ability to identify objects and other road users, such as pedestrians.
“We’re integrating radar and lidar sensors into headlights that are already there anyway – and what’s more, they’re the parts that ensure the best possible transmission for optical sensors and light sources, and are able to keep things clean,” said researcher Tim Freialdenhoven.
Lidar, which can be used in electronic brake assist or distance control systems, operates using a measuring principle based on determining the time between a laser pulse being emitted and the reflected light being received.
In the integrated headlight, light beamed onto the road cannot be impeded by the two additional sensors, so the researchers are positioning the lidar sensors at the top and the radar sensors at the bottom of the headlight casing.
At the same time, the beams from both sensor systems need to follow the same path as the LED light – something made more difficult by the fact that all the beams involved have different wavelengths. The visible light from the headlight measures 400-750nm (nanometres), while infrared lidar beams are 860-1,550nm, close to the visible range. Radar beams, on the other hand, have a wavelength of 4mm.
“These three wavelengths need to be merged coaxially – that is, along the same axis – and this is where what we call a multispectral combiner comes in,” said Freialdenhoven.
‘Bi-combiners’ use a dichroic mirror with a special coating to combine the LED and lidar rays, guiding the two ‘beam bundles’ along a single axis by means of wavelength-selective reflection. The same effect happens in a second combiner, where the LED and lidar beams combine with the radar.
As radar sensors are already in widespread use in the automotive sector, bi-combiner designs must allow manufacturers to continue using existing sensors without the need for modifications.
Combining all three systems can make the most of their strengths while minimising their weaknesses, Freialdenhoven said.
Optical systems, for instance, have limited performance in situations where visibility is poor, such as foggy and dusty environments. Radar systems, on the other hand, can see through dense clouds of fog but are not very good at categorisation – although they are able to tell whether something is a person or a tree, lidar systems offer much more detail.
“We’re also working on merging data from radar and lidar – something which will add huge value, especially when it comes to reliability,” said Freialdenhoven.
The technology could create additional options for integrating sensors into driver assistance systems, the researchers said. Smaller light modules, more compact lidar sensors and integrated radar will make it possible to create multi-sensor concepts. Future self-driving systems might be able to not only detect a person, but also analyse their speed, how far away they are, and their angle to the vehicle.
The team is working to create a prototype following the patent application.
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