People use their eyes and ears to learn about potentially dangerous traffic situations. For self-driving cars to be able to do the same, they need a lot of sensors. However, as the number of sensors they contain increases, so does the amount of space required to install them, which is often inconsistent with the designer’s vision.
Now researchers at Fraunhofer-Gesellschaft have found a way to carefully integrate certain sensors. Their solution lies in vehicle headlights, where they combine optical lights, radar and lidar.
Modern cars are able to perform more and more functions on their own, without the participation of the driver. Cruise control automatically maintains the correct distance from the vehicle in front, lane departure warning corrects the vehicle’s trajectory if necessary, and if the driver is caught off guard, emergency braking is applied.
All this is possible thanks to cameras in the cabin and radar sensors in the grille – and in the future, cars will do more on their own. Achieving this requires using more sensors, but car designers aren’t keen on stuffing them into the grille.
Five Fraunhofer institutes, including the FHR Institute for High Frequency Physics and Radar Technology, have joined forces in the Smart Headlights project to create a sensor mounting method that is as compact as possible. Slim – Does not affect functionality or performance. .
The aim of the project was to develop a headlight with an integrated sensor for driver assistance systems, which would combine a number of sensor elements with an adaptive lighting system. This will hopefully improve the sensor’s ability to identify objects on the road, especially other road users such as pedestrians. For example, lidar sensors can be used in electronic brake assist systems or distance control systems.
“We are integrating radar and lidar sensors into existing headlamps – and more importantly, they are the parts that ensure optimal transmission of optical sensors and light sources and keep them clean,” says Tim Fever Raunhofer, researcher at FHR Freialdenhoven. LiDAR (Light Detection and Ranging) sensors operate on a measurement principle based on determining the time between the emission of a laser pulse and the receipt of reflected light. This method provides very accurate distance measurements.
The first step in building a headlight sensor involves developing a LiDAR system suitable for integration into automotive technology. This also takes into account the fact that the light from the headlights on the road is not blocked by the two additional sensors, even if the LEDs responsible for lighting are located farther from the headlights.
For this reason, the researchers placed the lidar sensor at the top and the radar sensor at the bottom of the headlight housing. At the same time, the light beams from the two sensor systems must follow the same path as the LED light, which is more complicated since all the light beams involved have different wavelengths.
Headlamps emit visible light in the range of 400 to 750 nanometers, while LiDAR infrared beams have a range of 860 to 1550 nanometers, which is close to the visible range. On the other hand, the radar beam has a wavelength of four millimeters. “These three wavelengths need to be combined coaxially, that is, along the same axis, and this is where what we call a multispectral combiner comes into play,” Freialdenhoven said.
This coaxial beam direction is important to prevent complex parallax errors. In addition, placing the sensors next to each other takes up more space than a coaxial configuration, which is why researchers are using so-called dual combiners to solve this problem.
To combine LED and LiDAR light, the solution uses a specially coated dichroic mirror that directs two beams along the same axis through wavelength-selective reflection. The same effect occurs in the second combiner (albeit in a more complex manner due to the very different wavelengths), where LED light, LiDAR light and radar are combined.
Because radar sensors are already widely used in the automotive industry, the dual-totalizer design should allow manufacturers to continue using existing sensors without modification.
So why combine optics, lidar and radar? “Each individual system has its advantages, but also its disadvantages,” Fraialdenhoven explains.
For example, optical systems exhibit limited performance in poor visibility conditions such as fog and dust. Radar systems, on the other hand, can handle thick fog with ease, but are not very good at classifying: while they can tell if someone is a person or a tree, their ability has no advantage over LiDAR systems.
“We are also working on combining radar and LiDAR data, which will bring huge benefits, especially in terms of reliability,” Freialdenhoven said. The team has applied for a patent and is currently working on a prototype.
The technology is designed to create numerous additional options for integrating sensors into driver assistance systems. Smaller optical modules, more compact LiDAR sensors, and embedded radar sensors will enable multi-sensor concepts, especially in autonomous vehicle technology with increasingly stringent design requirements and limited installation space.
Therefore, future autonomous driving systems can not only detect a person, but also analyze his speed, distance and angle of his location relative to the vehicle.
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Post time: Oct-31-2022
