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The article talks about eye safety a bit in section 4. > a stuck mirror This is one of the advantages of using an array of low power lasers rather than steeri
by dllu 10mo ago
The article talks about eye safety a bit in section 4.
> a stuck mirror
This is one of the advantages of using an array of low power lasers rather than steering a single high power laser. The array physically doesn't have a failure mode where the power gets concentrated in a single direction. Anyway, theoretically, you would hope that class 1 eye-safe lidars should be eye safe even at point blank range, meaning that even if the beam gets stuck pointing into your eye, it would still be more or less safe.
> 20 cars at an intersection = 20 overlapping scanners, meaning even if each meets single-device Class 1, linear addition could offer your retina a 20x dose enough to push into Class 3B territory.
In the article, I point out a small nuance: If you have many lidars around, the beams from each 905 nm lidar will be focused to a different spot on your retina, and you are no worse off than if there was a single lidar. But if there are many 1550 nm lidars around, their beams will have a cumulative effect at heating up your cornea, potentially exceeding the safety threshold.
Also, if a lidar is eye-safe at point blank range, when you have multiple cars tens of meters away, laser beam divergence already starts to reduce the intensity, not to mention that when the lidars are scanning properly, the probability of all of them pointing in the same spot is almost impossible.
By the way, the Waymo Laser Bear Honeycomb is the bumper lidar (940 nm iirc) and not the big 1550 nm unit that was on the Chrysler Pacificas. The newer Jaguar I-Pace cars don't have the 1550 nm lidar at all but have a much bigger and higher performance spinning lidar.
- ErroneousBosh 10mo ago> > a stuck mirror Detect the mirror being stuck and shut the beam off. Easy. Hint: how bad would it be if the MCU in your gas heating boiler latched up and wouldn't shut the burner off? How is this mitigated?
- marcellus23 10mo agoThis was addressed in the original comment: > Additionally, no LIDAR manufacturer publishes beam-failure shutoff latency. Most are >50ms, which can be long enough for permanent injury
- ErroneousBosh 10mo agoYou should be able to do it way faster than that.
- snypher 10mo agoPressure switches, flow sensors, mechanical flame detectors, power supply monitoring, watchdog timers, and XX years of Honeywell or whoever knowing what they are doing. So yes, a mirror trip reset is probably a good start. But would I trust someone's vision to this alone?
- ErroneousBosh 10mo ago> Pressure switches, flow sensors, mechanical flame detectors, power supply monitoring, watchdog timers, and XX years of Honeywell or whoever knowing what they are doing. Nope, nothing as complicated as that. You're close with the watchdog timer. The solenoid is driven by a charge pump, which is capacitively coupled to the output of the controller. The controller toggles the gas grant output on and off a couple of times a second, and it doesn't matter if it sticks high or low - if there's no pulses the charge pump with "go flat" after about a second and drop the solenoid out. Do the same thing. If a sensor at the edge of the LIDAR's scan misses a scan, kill the beam. Same way we used to do for electron beam scanning.
- toss1 10mo ago>> if there's no pulses the charge pump with "go flat" after about a second and drop the solenoid out. >> Do the same thing. If a sensor at the edge of the LIDAR's scan misses a scan, kill the beam. Sounds like a great plan, but I question the "about a second" timing; the GP post calculates that "about a second" is between 4X and 10X the time required to cause damage. So, how fast do these things scan/cycle across their field of view? Could this be solved by speeding up the cycle, or would that overly compromise the image? Change the scan pattern, or insert more check-points in the pattern?
- amelius 10mo ago> The array physically doesn't have a failure mode where the power gets concentrated in a single direction Ok, but now the software can cause the failure. Not sure if that's much of a relief.
- amelius 10mo agoFor the downvoters: https://en.wikipedia.org/wiki/Beamforming https://en.wikipedia.org/wiki/Beamforming It is possible for the array to produce a concentrated beam into one direction. The software determines when that happens and in what direction.
- dllu 10mo agoBeamforming with a phased array is talked about in the article, but you are conflating two very different types of arrays. You can't form beams with the types of macroscopic arrays I was referring to, since they consist of macroscopic array elements whose phase cannot be controlled, and reside behind a fixed lens that ensures that they all point in different directions.