High Definition Lidar System
10. Sensor system of claim 8, wherein a plurality of detector printed circuit boards are mounted on the motherboard to form a second vertical stack, wherein the first vertical stack of transmitter circuit boards is positioned substantially parallel to the second vertical stack of detector circuit boards. One of the advantages of mounting transmitters and sensors on individual hybrid boards is the ability to then mount the individual hybrid boards on the motherboard in a vertically oriented configuration. In the version shown, the detectors are positioned in a first vertical orientation along a first vertical axis, while in a second vertical orientation, the transmitters are positioned along a second vertical axis, with the first and second vertical axes parallel and side by side. As best shown in Fig. 5 and 8, the hybrid boards that carry transmitters and detectors are mounted in vertical stacks that allow the sensor head to have a smaller diameter than a differently configured sensor with transmitters and detectors positioned around the perimeter of the system. As a result, the configuration reduces the overall size and requires less energy to rotate by moving more weight towards the center of the sensor. Examples of LiDAR systems are shown in Figures 1 and 2. In each case, a rotating housing emits pulses of light reflected from objects, allowing rear reflections to be detected by detectors inside the rotating housing. By rotating the housing, the system provides a 360-degree field of view (FOV) and, depending on the number and orientation of lasers in the housing, a desired vertical field of view.
The system is typically mounted in the upper center of a vehicle so that it has a clear view in all directions, and rotates at a speed of about 10 Hz (600 rpm), providing a high point cloud refresh rate, which is beneficial for autonomous navigation at higher speeds. In other versions, the rotational speed is between 5 and 20 Hz (300-1200 rpm). In this configuration, the system can acquire approximately 2.56 million TOF distance points per second. The system therefore offers the unique combination of a 360-degree field of view, high point cloud density and high refresh rate. The standard deviation of TOF distance measurements shall be at least 2 cm. The LiDAR system may include an inertial navigation system (INS) mounted on it to report x, y, z deviations and the pitch, roll and yaw of the unit used by navigation computers to correct these deviations. Fig. 5 shows the same version as in ABB. 3 and 4, but without the outer housing that covers the internal components. In general, and as shown in more detail below, the system includes a motherboard 20 that supports a plurality of hybrid detectors 32 and hybrid transmitters (not visible in Fig.
5). The transmitters refer back to the back of the system, where the pulses are reflected by a mirror and then passed through a lens 50. The reverse pulses pass through a lens, are reflected by a mirror 40 and then directed to the detectors integrated in the hybrids 32. The motherboard 20 and mirror 40 are mounted on a common frame 22, which provides common support and facilitates alignment. The separate position of the optical paths of transmitters and detectors can lead to a parallax problem. When transmitters and detectors are separated by a finite distance, there is always a “blind” area closest to the sensor where objects cannot be illuminated or detected. Similarly, the laser light from the transmitter is misaligned at long distances with the corresponding detector and creates a similar blind spot. The parallax problem is best illustrated in Fig. 10.
A representative transmitter 170 sends a light signal through a lens 172, in which the propagated light signal moves outward and towards a target in the distance. Light reflected from one target can return through a second lens 162 and further to a detector 160. However, the non-parallel orientation of the transmitter and detector creates non-parallel paths of the light emitter and detector. Therefore, there is a blind spot 180 next to the system and a blind spot 184 away from the system. In each of the two blind spots, light reflected from an object returns along a path that cannot be received by the detector. The near blind spot extends beyond the system to a distance “A” in front of the system, while the distant blind spot extends beyond the system in the distance region “C”. Between the two blind spots, at a distance defined by “B”, the system sees an object where light reflected from the object can return to a path that can be detected. Even within region B, however, there is a “sweet spot” 182, which is defined by the right paths from the transmitter to the detector. For those listed in the figs. 1 and 2, the “sweet spot” 182 for parallax alignment is about 100 feet from the center line of the sensor. Within a radius of about 10 feet, the light from the transmitter completely misses its corresponding detector, which is displayed at 180, and beyond about 240 feet, indicated at 184, the signal becomes weak due to misalignment of the transmitter and detector in the opposite direction. As shown in Figure 8, the preferred version comprises a plurality of detectors (in this case 32) mounted on an equal number of hybrid detectors 32.
The system also has the same number of transmitters mounted on an equal number of 30 hybrid emitters. In the preferred version, the system therefore has one transmitter per hybrid and one detector per hybrid. In other versions, this can be modified, for example, to integrate several transmitters or detectors on a single hybrid.
