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Short Distance Laser Range Finder - Change Estimator

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KTuncer

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Hi,

This is a subject that has been discussed extensively and there are great posts from EricGibbs. My problem is similar but there are a few catches so I wanted to ask here.

I am trying to design a laser range finder(not exactly read on) with 1mm or less accuracy over 300mm effective distance. For a reason we cannot use a collimated beam so I am using lasers with 10 degree half angle.

Current idea is to modulate the laser beam at a high frequency and look at the change in phase. Actually we don't even care about the absolute distance but change in distance in mm. I.e. getting closer or not. However this requires a very high frequency circuit and I am trying to find out if there is a better way.

Eric talks about hybrid logic/analog circuit to do this without a very high frequency counter and I am just curious if it could be applied here.

(https://www.electro-tech-online.com/threads/hellp-me-to-build-laser-range-finder.43169/)


Any ideas you can suggest would be great.

Thanks,
KT
 
I think you are using the wrong method for such a small distance.

Have you considered using a laser dot and some type of triangulation system? It could be as simple as a laser dot and a camera, or a laser dot and some other sensor that can detect the angle of the dot from the sensor. Maybe a rotating lens.

What is the application and why do you need better than 1mm accuracy?
 
The application is industrial. The shape of the objects are non uniform (i.e. one product to the next one), so I cannot be sure of the reflection of the object always with similar angle. Also, the object not only gets closer but moves on the horizontal plane, which will impact the angle. That is why I was looking at a way of trying this with laser.

In addition object moves really fast the 30-50fps sensors are useless and I don't want to fork out a 20K to buy a high speed camera to do this job, hopefully can be done with a few lasers, good electrical design and DSP under 100$.

Thx, KT
 
The application is industrial. The shape of the objects are non uniform (i.e. one product to the next one), so I cannot be sure of the reflection of the object always with similar angle. Also, the object not only gets closer but moves on the horizontal plane, which will impact the angle. That is why I was looking at a way of trying this with laser.

In addition object moves really fast the 30-50fps sensors are useless and I don't want to fork out a 20K to buy a high speed camera to do this job, hopefully can be done with a few lasers, good electrical design and DSP under 100$.

Thx, KT

hi KT,
The types of lasers I designed and manufactured were for the hydro-graphic surveying market, used for range finding from 2m to 5000mtrs with a +/-0.25% accuracy.
The 25Watt, 904nm laser diodes were pulsed on for 30nSec at a 400 p/s rate, which would be unsuitable for your application.
 
That's some pretty tall order specs KTuncer! Objects moving at 50 feet per second? Laser ranging <1mm? :eek:

I think a pro engineer who already has HF/RF experience and laser range finder experience would still find that a tough project, and charge thousands.

What are the objects, how big are they and how much space between objects on the conveyor? I might have another solution... ;)
 
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