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[DPRG] Phase Shift

Subject: [DPRG] Phase Shift
From: ray xu rayxu at tx.rr.com
Date: Fri Jul 25 11:38:10 CDT 2008

I still want to use different methods besides TOF.  I thought about your
idea, and it seams possible to me.  So you're saying that to measure
distance, I point a laser at a slight angle, towards the CCD and let the CCD
measure how far that laser dot is from center pixel?  Will this be effective
for long ranges, like up or more than 6 meters?  

___________________
Ray Xu
rayxu at tx.rr.com
DPRG member
OOPic group member
Seattle Robotics group member
My Blog


-----Original Message-----
From: Tom Brusehaver [mailto:cozytom at gmail.com] 
Sent: Tuesday, July 22, 2008 3:33 PM
To: ray xu
Cc: dprglist at dprg.org
Subject: Re: [DPRG] Phase Shift

There was a very clever trick that one guy used. The article was in
circuit cellar
about 10 years ago.

Using a linear CCD (like out of a scanner), it measures the angle offset
from the laser and the CCD.

don't point the laser straight ahead, but at a slight angle. The reflection
will traverse the CCD. Some quick trig, and you can get an angle.



On Tue, Jul 22, 2008 at 12:40 PM, ray xu <rayxu at tx.rr.com> 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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