|
|
|
|
|
| |
Posted by Miem on May 14, 2006, 12:10 pm
Please log in for more thread options
As it may be obvious from my question, I am novice to optics. And I'm
aking friendly expert advise. My hypotethical scenario is sketched to
learn about how to use polarized light in indoor and outdoor robotics
applications.
What I would like to do is to determine the relative attitude of two
mobile robotic platforms, or the attitude of a mobile robot relative to
a stationary node. It is easier to explain my question by using the
second example
Imagine and that we have a light source projecting vertically polarised
light to a wall or to a screen. Assume also that we have a receiver
sensor on the mobile platform with a polarising filter in front of it,
and it is pointed toward to the same wall/screen. Depending on the
relative angle of the polarised light source the receiver's polarizing
filter, we will measure different intensities.
If we rotate the receiver's polarising filter continuously, in ideal
situation, I would expect to observe a sinusoidal wave form for the
measured light intensity. Instead of dealing with the absolute
intensity values from the receiver sensor, if you detect the peak of
the sinusoidal wave then we may find the best alignment with the
projected light and the receiver polarizations. Since we know the
rolative angle of the receiver filter with respect to the our mobile
platform, we can find the relative angle/attitude of our robot with
repect to the light projecting node.
Now if we assume that the polarised light projector is mounted on a
mobile robot and it is pointing to another robot, then we can find the
relative angle of these two robots.
Questions;
1. If I put a linear polarizing filter (removed from low a cost 3D
glasses, any suggestion from where I can get a better one -low cost
please-) infront of our light source and project the light to an
ordinary wall, due to the uneven surface of the wall will we lost the
the polarization ?
2. How to make a wall/screen which preserves the polarization of the
projected light?
3. Can we use either ordinary visible light (a light bulb) or a bunch
of IR LED as the light source behind the polarizing filter? (Do IR
light from the LED can be polarized as normal light?)
4. In an outdoor situation, if we have a long flat road and two
mobile robots on opposite ends of the road, pointing to each other, can
we use the above mentioned method to detect the relative angles between
the robots?
5. How daylight effect our polarized light experiment?
6. Can you suggest an "optical" method which allows us to determine
the rolative angle of two mobile robots seperated from each other by
100-200 meters? (Yes, it sound like a big ask!)
7. Thanks in advance for the friendly advices.
Cheers,
Miem Chan
|
|
Posted by on May 14, 2006, 12:33 pm
Please log in for more thread options
Miem wrote:
> 6. Can you suggest an "optical" method which allows us to determine
> the rolative angle of two mobile robots seperated from each other by
> 100-200 meters? (Yes, it sound like a big ask!)
Why does it have to be optical? Sounds like an ideal application of
low-cost accelerometers, unless there are special circumstances you
didn't describe.
You can use a laser to communicate between the two robots, if optics in
the loop is a "must" :)
To do it your way, I would suggest an added complication - modulate the
light source (say, 10kHz) and filter the other end to allow through
only this modulation before you start looking for those sinusoidal
peaks.
I take it you are assuming an acute angle here.
|
|
Posted by D Herring on May 16, 2006, 1:28 pm
Please log in for more thread options Miem wrote:
> If we rotate the receiver's polarising filter continuously, in ideal
> situation, I would expect to observe a sinusoidal wave form for the
> measured light intensity. Instead of dealing with the absolute
> intensity values from the receiver sensor, if you detect the peak of
> the sinusoidal wave then we may find the best alignment with the
> projected light and the receiver polarizations. Since we know the
> rolative angle of the receiver filter with respect to the our mobile
> platform, we can find the relative angle/attitude of our robot with
> repect to the light projecting node.
Unfortunately, this relative angle is coaxial with the direction of beam
propagation; thus it isn't useful in most mobile robotics tasks.
> Questions;
> 1. If I put a linear polarizing filter (removed from low a cost 3D
> glasses, any suggestion from where I can get a better one -low cost
> please-) infront of our light source and project the light to an
> ordinary wall, due to the uneven surface of the wall will we lost the
> the polarization ?
Check out edsci.com or scientificsonline.com for polarization filters.
Depending on the surface properties, polarization may or may not be lost
when reflecting off your rough wall. In fact, light can be polarized by
reflecting it off some materials at a shallow angle; hence "Rayban"
sunglasses have polarized lenses to help reduce this glare. At steep
angles (e.g. nearly perpendicular), I believe most surfaces preserve
polarization.
> 2. How to make a wall/screen which preserves the polarization of the
> projected light?
Check readily available surfaces with a pair of polarization filters
until you find one which fits your needs. Reflecting light off a screen
will greatly increase the power requirements.
> 3. Can we use either ordinary visible light (a light bulb) or a bunch
> of IR LED as the light source behind the polarizing filter? (Do IR
> light from the LED can be polarized as normal light?)
All light can be polarized. Polarizing filters block a certain
percentage of the light passing through them. Lasers can be designed to
generate polarized light, but these will generally be expensive.
> 4. In an outdoor situation, if we have a long flat road and two
> mobile robots on opposite ends of the road, pointing to each other, can
> we use the above mentioned method to detect the relative angles between
> the robots?
> 5. How daylight effect our polarized light experiment?
It will flood your optical sensors with stray light. You may need to
modulate your signal to help separate it from background noise.
> 6. Can you suggest an "optical" method which allows us to determine
> the rolative angle of two mobile robots seperated from each other by
> 100-200 meters? (Yes, it sound like a big ask!)
The dominant problem you will face is simply tracking. At that
distance, you will want to use lasers pointed directly between the
robots; other light sources would require hundreds of watts to operate.
Once you have a tracking system in place, you could query it for the
angle it is targeting. Use polarized light or two parallel beams to
obtain the rotation about the beam axis.
- Daniel
|
|
Posted by Gordon McComb on May 16, 2006, 2:31 pm
Please log in for more thread options D Herring wrote:
> All light can be polarized. Polarizing filters block a certain
> percentage of the light passing through them. Lasers can be designed to
> generate polarized light, but these will generally be expensive.
And somewhat hard to find now on the surplus market. In the old days,
laser printers and some laser disk players used polarized he-ne lasers
(using a Brewster window rather than a filter), and if you can locate
one in the junk pile you might find the tube still works. A common
polarized tube was the Toshiba LG-3217. Which reminds me that I've been
meaning to unload my cache of laser tubes and power supplies, which
include the 3217...anyone hit me up via EMAIL (not this list) if you're
interested.
A good hacking page for those into the good ol' days of glass laser
tubes:
http://straylight.cso.niu.edu/repairfaq/sam/laserpic/miscpics.htm
-- Gordon
|
| Similar Threads | Posted | | Moammar, still tucking, dares almost softly, as the determination continues in terms of their gentleman. | November 18, 2007, 1:33 pm |
| Re: Attitude and double standard of Customs Officer | September 21, 2007, 4:45 am |
| Re: Attitude and double standard of Customs Officer | September 22, 2007, 8:16 am |
| Re: Attitude and double standard of Customs Officer | September 22, 2007, 9:01 am |
| Low cost MEMs accelerometers, gyroscopes and magnetometers --> 3D Posisition and attitude | October 13, 2006, 12:28 pm |
| Relative Positioning | May 5, 2008, 2:17 pm |
| relative lowers Eve v response | August 19, 2007, 3:01 am |
| filthy cm relative to youth | August 14, 2007, 5:45 pm |
| relative to them ashamed swimmings | November 24, 2007, 9:36 am |
| Alexandra fosters relative except spread | August 19, 2007, 4:16 am |
|
|
|
XML site map
> the rolative angle of two mobile robots seperated from each other by
> 100-200 meters? (Yes, it sound like a big ask!)