3 ms·

PMD/IFM has been trying to drive their costs down for a while as well.

by rcv 9y ago

Animats 9y ago
That's a modulated carrier type system. Those aren't useful in sunlight, because they have to outshine ambient lighting continuously. Pulse-type devices only have to outshine the sun in a narrow frequency band for a nanosecond, which is quite possible.
- CamperBob2 9y ago
  That's the idea behind the modulation, though. It's relatively easy for the receiver to lock to the modulated AC frequency in the presence of sunlight ("DC" at baseband). Same concept as TV remotes that frequently use a 36-38 kHz carrier. If they just gated the IR LED on and off at the baseband data rate, interference from room light would be a problem.
  - Animats 9y ago
    Those things are fun. The idea is that you modulate the outgoing beam with a RF carrier, and measure the phase shift of the incoming beam relative to the outgoing beam. Today you can do this directly, because electronics is fast enough to count in the gigahertz range. It used to have to be done by superheterodyning, like a radio receiver. You down-convert both the incoming and outgoing signals using a local oscillator, and get two new signals at a much lower frequency. This transformation has the useful property that the phase difference between the lower-frequency signals is the same as the phase difference at the higher frequency. But at the lower frequency, it's easier to measure the phase difference. Also, you get the selectivity of a superheterodyne receiver. That's fine for a scanner, where you only need one copy of the electronics, but doing it for every pixel means something like a radio receiver behind each pixel. Still, you could probably do that now. The SwissRanger [1], a short-range time of flight imaging camera, worked like that. It's been discontinued. (I fooled around with this in the early 1990s, trying to build a laser scanner. Too many noise problems.) [1] http://hptg.com/industrial/ http://hptg.com/industrial/
    - CamperBob2 9y ago
      Yeah, that's an intriguing piece of hardware. A camera that outputs a Z buffer at conventional digital-photo resolutions and data rates would have lots of uses, but it sounds like it fell short of that goal.

PMD/IFM has been trying to drive their costs down for a while as well.

by rcv 9y ago

PMD/IFM has been trying to drive their costs down for a while as well.

That's a modulated carrier type system. Those aren't useful in sunlight, because they have to outshine ambient lighting continuously. Pulse-type devices only have to outshine the sun in a narrow frequency band for a nanosecond, which is quite possible.

CamperBob2 9y ago
That's the idea behind the modulation, though. It's relatively easy for the receiver to lock to the modulated AC frequency in the presence of sunlight ("DC" at baseband). Same concept as TV remotes that frequently use a 36-38 kHz carrier. If they just gated the IR LED on and off at the baseband data rate, interference from room light would be a problem.
- Animats 9y ago
  Those things are fun. The idea is that you modulate the outgoing beam with a RF carrier, and measure the phase shift of the incoming beam relative to the outgoing beam. Today you can do this directly, because electronics is fast enough to count in the gigahertz range. It used to have to be done by superheterodyning, like a radio receiver. You down-convert both the incoming and outgoing signals using a local oscillator, and get two new signals at a much lower frequency. This transformation has the useful property that the phase difference between the lower-frequency signals is the same as the phase difference at the higher frequency. But at the lower frequency, it's easier to measure the phase difference. Also, you get the selectivity of a superheterodyne receiver. That's fine for a scanner, where you only need one copy of the electronics, but doing it for every pixel means something like a radio receiver behind each pixel. Still, you could probably do that now. The SwissRanger [1], a short-range time of flight imaging camera, worked like that. It's been discontinued. (I fooled around with this in the early 1990s, trying to build a laser scanner. Too many noise problems.) [1] http://hptg.com/industrial/ http://hptg.com/industrial/
  - CamperBob2 9y ago
    Yeah, that's an intriguing piece of hardware. A camera that outputs a Z buffer at conventional digital-photo resolutions and data rates would have lots of uses, but it sounds like it fell short of that goal.