Robot position sensing

I heard of a commecial mobile robot that used a system consisting of a checkerboard pattern of black/white tiles on the floor. A sensor on the robot simply
noted when it went over a tile transition. Probably need to combine this with a direction sensor like a compass, though.
Also, has anyone mentioned using active ultrasonic beacons. A series of ultrasonic transmitters in known locations around the room. They would each transmit a pulse in sequence, and transmit an RF signal to the robot telling exactly when the ultrasonic pulse was transmitted and from which transmitter. The robot would receive the ultrasonic pulses and triangulate using the measured time of flight. Not good for a cluttered environment though.
Dave
"Guy Macon" <http://www.guymacon.com wrote in message

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On Mon, Feb 23, 2004 at 09:39:21PM -0800, wrote:

A commonly used method for airplane navigation utilizes a ground based transmitter that emits an omni-directional broadcast in combination with a rotating directional beam. It works by first sending out the omnidirectional pulse. Then the rotating beam rotates at a known rate 360 degrees, at which time another omni-direction pulse is sent out. Thus, the receiver times the difference between the two pulses and can thus determine direction to the transmitter. With two of these receivers, each tuned to a different transmitter, a precise position can be determined using triangulation.
A similar technique could be used using IR or other transmissions instead of radio where it may be hard to make a small directional broadcasting antenna, not to mention playing with actual radio beacons may require a license.
-Brian
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Brian Dean, snipped-for-privacy@bdmicro.com
BDMICRO - MAVRIC & MAVRIC-II ATmega128 Based Dev Boards
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See "VOR".

Or you could add distance measuring equipment (DME). The technology has been working for aviation for a loooong time, so it can't be *too* difficult to implement with modern technology.
Only needing a single beacon would be handy.
--kyler
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Is this similar to a Doppler Direction Finder? What does VOR stand for so I can search the net for implementations? Any other lead is welcomed.
Thanks,
Brian Dean wrote:

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Stephane Gauthier
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Stephane Gauthier wrote:

VOR = VHF Omni Range
VHF = Very High Frequency (30 to 300 MHz)
Jerry
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On Wed, Feb 25, 2004 at 02:22:55PM -0500, Stephane Gauthier wrote:

I'm not familiar with how that works.

As someone else mentioned, it stands for VHF Omnidirectional Range, VHF being Very High Frequency.
Other interesting navigational aids are NDB's - Non-Directional Radio Beacons. If I recall, these stations are usually located very near the airport and transmit a continuous morse code signal that identifies the station, but is also picked up by a special receiver on the plane (called an ADF - Automatic Direction Finder, or something like that) that can determine direction to the station. I recall these being primarily used for short range - designed to help you find the airport once you get close.
It's been a long time since I've piloted, but I suspect GPS has replaced most of these methods these days, or at least these other methods are probably used primarily as a backup to GPS. I'm just guessing at that, though.
-Brian
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NDB's--Still in limited use. Can still be found at many airports, and is considered a non-precision approach. I've nailed the airports dead on with it, and I've missed airports by a wider margin than I care to admit.
ADF's--also still used. Primarily with the NDB's, but you can also use it to guide you to your favorite AM radio station.
VOR's--One of the previous posters hit it dead on in how it works, and is still in use throughout aviation.
LORAN--has it's origins in WWII, and is still in use. (In fact, I fly off Loran more often than VOR or GPS).
GPS--the future of aviation that is already here today. Fantastic, accurate, very low failure rates, easy to use! A Pilot's dream. The previous systems are often times referred to as 'on their way out'. The reality is that the government continues to fund the continued operations of the previous mentioned equipment. I am sure someday they will go the way of the
Inertial Navigation Systems--Used on the big boys--constantly updated themselves off of the VOR's and other navaids. Very expensive systems. About 10 years ago, a cousin who flies 767's thought a handheld GPS was more accurate than their inertial navigation system.
ILS--Instrument Landing System. Considered a precision approach to an airport--if everything works right, there is no excuse to miss the runway. Uses two different transmitters--one at the approach end of the runway to give vertical guidance, one at the far end to give horizontal guidance.
Dead Reckoning--where by the pilot flies with a map, compass, and stop watch.
Celestial Navigation--I believe it was used by at least the military until at least Vietnam. One of the early cruise missiles used celestial navigation, as I recall.
Visual Aural Range (VAR)--look it up, as it is a technology that I have never really tried to understand.
Ground Direction Finding--Similar to the ADF's, but ground stations 'listened' to the aircraft's transmission signal, and then they were able to triangulate it's position and call the pilot back with recommend courses.
Air Surveillance and Precision Approach and Radar Control System (SAR)--whereby the air traffic controller has a specialized radar that provides them with a very precise set of information of the aircrafts position, direction, speed. They can talk a pilot down through the muck with it--I think this has it's origins clear back in to WWII, and is still available today at many control centers.
Airport Beacons--those little rotating lights at the Airport--that's so that Pilots can visually find the damned things.
Compass.
Another way of Navigation:
Shadowing--one of the first torpedoes that could be airdropped on a submarine used this approach (World War II). It it heard the 'noise' (in this case, the sounds of the propellers from a U-Boat) and turned towards that noise. If it was on the left, then it would turn left. If it was on the right, it would turn right. If it heard nothing (as in, the source of the noise was straight ahead,), then it ran straight. I think GE and the early precursor to MIT were the developers. Probably some information on that on line.
I have heard that they can map the magnetic forces of the earth, and get some fairly precise navigation from that.
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The most accurate would be to have a human pick up the robot and put it over a little dot on the floor. The robot would know for sure where it is.
There's also the separate overhead camera that looks down, and communicates this with the robot. Robot soccer uses this. Easier to implement than a patterned floor, and these days very cheap. Localizing can be a problem under desks and such (same with most other sensor systems), but a fusion of other techniques like odometers could provide intermediate positioning information untilt he robot is back into the clear.
But I have a reverse question for you: if you're in a room, do you know where you are absolutely? Or by looking around do you know where you are relatively? If you were to navigate through a room, especially one that is new to you, do you really need absolute position? Wouldn't you be looking for features that indicate such things as doorways and pathways, rather than distances from walls?
In other words, does a robot really need to know it's 2.457 feet from the northeast corner of the room, or does it need to know there's an old sock in the middle of the floor that it must steer around or roll over?
-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza
Guy Macon wrote:

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Let's assume that it's a sock-picker-upper robot... :)
Knowing where you are relative to the walls, door, etc is indeed sufficient to navigate. I was being imprecise in my use of the phrase "relative positioning" when I was referring to dead reckoning - knowing where you are relative to where you were before. The problem. of course, is that dead reckoning errors accumulate.
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Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
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This is true for animals with eyes. The only reason for absolute positioning for a robot is too make up for the lack of eyes.
The camera over the robot works a treat. However in a house you would need a camera in every room and passage.

Obstacle avoidance and navigation are two issues I think.
The absolute positioning problem will vanish when robots start using more sophisticated sensory equipment along with the computing power to use that equipment.
In the meantime we will be playing around with ad hoc structured environment solutions trying to get our sensory deprived and dumb machines to be something more than a remote control car made to look like a robot.
John Casey
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