12-04-2021 | | By Robin Mitchell
Recently, Intel announced that STMicroelectronics has been chosen to provide MEMS micro-mirrors for their RealSense High-Resolution LiDAR camera. Why are MEMS mirrors highly ideal for LiDAR, what is the L515, and how will it help with vision systems?
Light Detection And Ranging, or LiDAR, is a vision technology that uses a beam of light (almost always a laser), to measure the distance between itself and a target object. However, instead of ranging a single point source, LiDAR scans the area in front of them to create 2D distance maps of their surroundings, and this can allow a computer system to identify obstacles and objects.
In order for LiDAR to function, a laser beam is required to scan an area, and the first LiDAR systems would achieve this using rotating mirrors. While rotating mirrors are a cheap and effective method, it is also extremely bulky. The use of rotating mirrors also introduces wear and tear on bearings, and rotating systems can only operate so fast meaning that a LiDAR system using rotating mirrors can struggle with either resolution or frames per second.
However, LiDAR designers are beginning to move away from rotating mirrors towards MEMS mirror. A MEMS mirror is a miniature mirror fabricated on a semiconductor that is often attached to other mechanical components that flex under a voltage. As such, the mirror can be made to deflect at specific angles very fast, and the lack of bearings eliminates mechanical wear and tear. Of course, the most important benefit of a MEMS mirror is its size; a rotating LiDAR mirror system can be reduced in size from a large 20cm3 container to a device the size of a webcam.
Intel is famous for producing central processing units and memory technologies, but these are not the only products that Intel manufacture. Recently, Intel announced the development of its miniature LiDAR system, the L515, and also announced that they would be using STMicroelectronics MEMS technology for the mirror.
The RealSense L515 is a small LiDAR imaging system that has a diameter of 61mm and a height of 26mm. The device allows for continuous scanning of its environment, provides a resolution of up to 1024 x 768, has a frame rate of 30fps, and a depth of field view of 70° × 55°.
The minimum distance which the L515 can measure is 25cm, the maximum distance of measure is 9 meters, and has a measuring accuracy of 5mm to 14mm. However, the system also has an RGB sensor for imaging, and this has an output resolution of 1920 x 1080, a frame rate of 30fps, and a depth of field of 70° × 43°.
“With 30 frames per second and a field-of-view of 70° by 55°, ST’s 2nd-generation micro-mirror continues to set the bar for 3D scanning and detection applications. Continuing the long-term supply relationship for micro-mirrors with Intel demonstrates our never-ending efforts to leverage our long-lasting leadership in MEMS to meet the demanding technical and supply needs of our customers.”
- Benedetto Vigna, President Analog, MEMS and Sensors Group, STMicroelectronics.
Before looking at the specifics behind the L515, we first need to understand the benefits of LiDAR. LiDAR is a particularly unique vision technology as the image produced is a depth map whereas an image taking with a standard camera preserves no distance at all (unless two cameras are used and combined to take advantage of the parallax effect).
While there are other distance measuring technologies such as ultrasonic and RADAR, neither of these technologies provides the same resolution over the same distances. Ultrasonic is ideal for close ranging but is difficult to use for generating 2D surface maps, and RADAR is ideal for very long ranges.
The advantages of the L515, however, extend further than the base advantages of LiDAR as a depth detection technology. The most important feature of the L515 is its size; the small “hockey-puck” design is easily mountable on robotic systems. The second important feature of the L515 is its resolution; 1024 x 768 pixels is far more than enough for a robotic system to be able to recognise its surroundings. The third important feature is the combined camera and frame rate; 30fps is more than sufficient for a robotic system, and the use of a combined camera allows a system to perfectly overlay the depth map onto the visual image.
Overall, the L515 demonstrates the importance of micro-mirror MEMS in LiDAR systems, and how creating small LiDAR systems will enable the next generation of robotics.