DPRG mailing list archives: [DPRG] Phase Shift

Tue Jul 22 12:40:20 CDT 2008

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
>