DPRG mailing list archives: [DPRG] Phase Shift

Tue Jul 22 13:39:17 CDT 2008

I believe the "tricks" of the $$$ sensors involve multiple sampling  
methods and intense signal processing.

Other ideas include stereo vision and shape-distortion.  Stereo  
vision is self-descriptive.  Shape distortion is where you have a  
plurality of lasers, each are spread so that they draw a line in  
space.  Those lines intersect in ways that draw a shape on a 2-D  
surface (as if you were holding a piece of paper in front of the  
sensor.  Each laser is oriented such that the shape would change in a  
distinct manner as you moved the piece of paper toward and away from  
the sensor.  A 2-D camera captures the shape and a computer attempts  
to calculate the distance.  The major problem with this method is  
attempting to "see" the pattern on a non uniform surface (both  
physical distortion and variable reflectance).

!!Dean

On Jul 22, 2008, at 12:40 , ray xu wrote:

> Then if phase shift wont work, what methods are there to find the  
> absolute
> distance (besides triangulation and time of flight)?  What are those
> "tricks" (or any other details)?
>
> ___________________
> Ray Xu
> rayxu at tx.rr.com
> DPRG member
> OOPic group member
> Seattle Robotics group member
> My Blog
>
>
> -----Original Message-----
> From: Dean Hall [mailto:dwhall256 at gmail.com]
> Sent: Tuesday, July 22, 2008 12:31 PM
> To: ray xu
> Subject: Re: [DPRG] Phase Shift
>
> Sorry, I assumed you meant frequency shift when you said phase
> shift.  My statement (corrected): a single frequency shift reading
> doesn't give range.
>
> Measuring phase shift alone can give you a change-of-distance, but
> not absolute distance.
>
> The hokuyo sensors do some clever combination of laser readings.  The
> most telling paragraph that I can find says, "Since the speed of
> light would require Ghz or better timing for the ranges used by the
> rangers, there are tricks employed with pulsed laser light to view
> phase change of the pulses which greatly reduces the absolute timing
> requirements of the internal sensor/laser interfacing circuitry."
>
>  From http://www.acroname.com/robotics/info/articles/laser/laser.html
>
> !!Dean
>
>
> On Jul 22, 2008, at 09:32 , ray xu wrote:
>
>> But doesn't sensors like the Hokuyo sensors work with phase shift?
>> Are
>> there any other ways?
>>
>> ___________________
>> Ray Xu
>> rayxu at tx.rr.com
>> DPRG member
>> OOPic group member
>> Seattle Robotics group member
>> My Blog
>>
>>
>> -----Original Message-----
>> From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]
>> On Behalf
>> Of Dean Hall
>> Sent: Tuesday, July 22, 2008 9:15 AM
>> To: dprglist at dprg.org
>> Subject: Re: [DPRG] Phase Shift
>>
>> A phase shift won't give you the range to an object, only the speed
>> of that object with respect to the sensor.
>>
>> !!Dean
>>
>>
>> On Jul 22, 2008, at 08:55 , ray xu wrote:
>>
>>> Hi, I'm moving on from using complex high speed circuits for my
>>> laser range finder to using other methods like phase shift; I
>>> understand little about this, can someone explain it to me?  Also,
>>> is there any way of measuring phases that are off by as little as 1
>>> ns?
>>>
>>>
>>> Thanks.
>>>
>>>
>>> ___________________
>>> Ray Xu
>>> rayxu at tx.rr.com
>>> DPRG member
>>> OOPic group member
>>> Seattle Robotics group member
>>> My Blog
>>
>
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