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Registered Member #2063
Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352
Does laser rangefinders have a nanosecond stop watch that starts when the laser is on and stop when the sensor detected the laser has hit something solid? speed of light = 299 792 458 m / s 1 nanosecond = 0.000000001 seconds so lasers must travel 0.299792458 m / nanosecond
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
Measuring the time can indeed be done. I've seen a presentation of a 2dim sensor that incorporates about 128x128 APD + counter cells put on top of a readout backplane chip. Combined with a simple still frame camera, this beast was able to capture high power laser pulses from a multiwatt IR laser. This portable unit could deliver one-shot texturized 3d scenes. The spatial resolution is, as you no doubt have guessed, limited. Nevertheless, you can also modulate the Laser instead of using pulses. The simplest approach would be to use a periodic signal and derive the phase shift in respect to the transmitted signal. The phase shift is proportional to a modulo of the distance.
you can use e.g. 100 MHz modulation and a 99.9 MHz reference signal, mix it with both outgoing and incoming signal and retrieve amplitude and phase angle, just like it is done in a lock-in amplifier (you need 0deg and 90deg shifted reference signals for this). Combined with a rough measurement one derives the integer part of the distance. Multiple frequencies can also be used to pin down the actual distance.
Edit: found it! Check out
There are even more setups in use, like the time-to-amplitude converter which is also used for lifetime measurement, time-of-flight measurements and coincidence measurements. Think of it as an integrator with start and stop toggles. You can use the "stop watch" toggles to measure a short time duration and perform the AD-conversion later on.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I am working on a similar project from Boeing, we published some findings a while ago for our system at I can't tell you how much we have improved since, but its significant
One tricky bit with laser range finding in general is the issue of multiple reflections, ideally you would record a graph of power vs time so you can look at the various reflections you got and decide which one is the object you are looking for--but this requires some non-trivially complex rf design. For simple applications you can get away with a simple threshold system, where you record the first time your pulse hits above a certain threshold and record that time.
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concept of a laser rangerfinder?
