In essence, the laser pointer is best at ranging. Therefore, autonomous vehicle manufacturers often need to use it with the camera and millimeter wave radar to more fully grasp the three-dimensional information of the surrounding environment of the vehicle.
LiDAR is an active sensor, not a passive sensor that relies on ambient light like a camera. LiDAR emits a laser beam through a laser pointer, receives a beam reflected from a distant object, and obtains distance information of a distant object by measuring the time of flight of the beam. However, the laser beams are very narrow and they do not scatter (this is the point), so a single beam of LiDAR pulses can only perceive a very small object. That is, it may be able to detect a dime in 50 steps, but cannot detect a tall building.
Therefore, for practical applications, LiDAR sensors must perform some form of "scanning." This ultimately became a differentiating factor among many LiDAR manufacturers. Most LiDAR sensors are connected to a drive motor that rotates them. Once the laser emission is synchronized with the motion of the motor, we can know where the laser is pointing and combine the overall imaging of the front environment. Therefore, the field of view of LiDAR is completely dependent on the angle at which the motor rotates it. Currently, many LiDAR manufacturers use mirrors or MEMS micromirrors to deflect laser beams or project laser beams, while Cepton, a supplier of 3D LiDAR solutions in Silicon Valley, USA, has what it calls MMT (micro-motion fretting). patented technology.
Cepton CEO Jun Pei (裴军) has been reluctant to share too much detail about how its micro-motion technology works, just that it is a bit like a speaker cone in a speaker. That is, Cepton's LiDAR array moves, but does not use mirrors or drive motors. Therefore, Cepton's laser pointer avoids the inevitable light loss of the mirror and also eliminates any possible mechanical wear. Yan Jun said that this is a frictionless system that is reliable, cost effective and easy to manufacture.
According to the report of Memes Consulting, the US Patent and Trademark Office recently published a patent for invention of the LiDAR system scanning device and method applied by Cepton. We can get an idea of the structure and operating mechanism of the Cepton scanner.
Figure 3 illustrates the basic structure of a 3D imaging LiDAR sensor (100). The LiDAR sensor includes a fixed transmit lens 130 and a receive lens 140. And laser pointer light sources 110a-110b disposed substantially at the back focal plane of the emitting lens 130. Laser source 110a is used to emit laser pulses 120. The laser pulses are collimated by the emitting lens 130 and directed toward the object 150 in front of the LiDAR sensor.
The laser pulse 122 reflected from the object is then directed toward the receiving lens 140. The photodetectors 160a-160b are disposed substantially at the focal plane of the receiving lens 140 by the receiving lens 140 focusing to the respective photodetectors 160a-160b.
Finally, the distance between the laser pulse 120 and the detected time of flight (ToF) is determined by the processor 190 coupled to the laser source 110a and the photodetector 160a, thereby calculating the distance between the LiDAR sensor and the object.
In the LiDAR sensor, the laser pointer (110a to 110d) and the photodetector (160a to 160d) are two-dimensionally scanned flexure mechanism (200), and the four laser sources 110a to 110d and the four photodetectors 160a to 160d are mounted on the same rigidity. On platform 230. The rigid platform 230 is coupled to the first substrate 210 by two flex members 220a and 220b. The flex members 220a and 220b can be deflected left or right by using a single actuator (eg, voice coil 250 and permanent magnet 260, or by piezoelectric actuators, etc.). The first substrate 210 may be coupled to the second substrate 212 by two flex members 270a and 270b. The flex members 270a and 270b can be deflected forward or backward using a single actuator (eg, voice coil 252 and permanent magnet 262, or by piezoelectric actuators, etc.).
Thus, by the left and right movement of the flex members 220a and 220b, and the forward and backward movement of the flex members 270a and 270b, the laser pointers 110a-110d and photodetectors 160a-160d can be in the focal planes of the transmit lens 130 and the receive lens 140, respectively. Perform a two-dimensional scan.