ultrasonic sensors => maxsonar EZ-1, SRF0x, or PING



Is it possible that some of the sensors that can't measure close up (with a 6" limit for example) will return an unknown or max distance response when objects are too close? If so, this would prevent the bot from "seeing" things that were right in front of it and could be a reason for using the sensors that would not so blind to close objects.
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Curt Welch http://CurtWelch.Com /
snipped-for-privacy@kcwc.com http://NewsReader.Com /
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On 22 Dec 2006 05:31:08 GMT, snipped-for-privacy@kcwc.com (Curt Welch) wrote:

My mini-sumo Seeker 2 suffers from this, so I built a near-IR sensor. The Sharp GP2D12 analog sensors reach their minimum value at a distance of 10cm, and then as the object gets closer, the value the sensor returns starts getting farther away. The near IR sensor only detects things out to about 10-12 cm, so in combination I can get a better idea if the opponent is really close.
http://www.huv.com/miniSumo/seeker2
There's a closeup of the sensor here:
http://www.huv.com/near-ir.jpg
It uses a Sharp IS471F as the detector/LED driver, and a normal IR led wrapped in heatshrink.
Later, Jon
-------------------------------------------------------------- Jon Hylands snipped-for-privacy@huv.com http://www.huv.com/jon
Project: Micro Raptor (Small Biped Velociraptor Robot) http://www.huv.com/blog
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Gordon McComb wrote:

The issue isn't so much that you need to know when your .1" away from something as it is if you are 5.9" or 5.8" ... 1.1" 1.0" etc. Actually, the application was CAN CAN, and the particular use was to home on a can to be grasped by the "big gripper", and indeed accurate distance and positioning in the sub inch range was necessary to know when to close the gripper, as the setup was constructed. The sonar did much better in that function than it did in the general ability to distinguish the can from the wall.
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear
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RMDumse wrote:

Contact and near-contact sensing for gripping applications is another matter altogether, and there are numerous concepts floating around in addition to ultrasonic, such as microphonic induction, flex strain cells, etc. Your original message coupled ultrasonics with wider view sensing, which is far less predictable.
My point was that one sensor for everything, especially where the face of the sensor is not parallel to the sensed surface, will natually yield poor results. These are chronically simplistic devices we attempt to shoehorn into incredibly complex roles. Ultrasonics are basically useful for seeing what is directly in front of you, and for measuring the distance to parallel walls on either side. Readings at obtuse (or greater than critical) angle are basically useless, so the idea is to avoid that scenario altogether. It's hard to overcome physics.
There are some very cheap and reliable near-contact light sensors that Sharp sells that are more-or-less immune to ambient light interference. They change their lineup all the time, but I recall they have a number of go/no-go sensors for the 3-12mm range. However, they'd only be useful for that last few millimeters before contact is made.
-- Gordon
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RMDumse wrote:

I have to double-down on what Randy has said here. First, I tried the SRF04 but found it had some nasty sidelobe pickup, even from objects that were >12" away. I haven't tried the maxsonar, but ended up using several Ping sonars and like them a lot. No nasty sidelobes, however, I did find they seem to suffer from multiple reflections [as I imagine all sonars will] when the distance to a wall for instance is very short, and the angle is *not* perfectly perpendicular. I concluded the multiple reflections were coming back from the robot itself ... sonar Tx -> wall --> robot --> wall --> sonar Rx.

like this on anything flying around. OTOH, a really good sonar would be smart enough to make multiple samples on the environment, using a set of difference Tx energies, in order to correlate target distances against energy level required to produce an echo.
BTW, Joe Jones in his book Robot Programming spends a lot of time talking about sensor unreliability and the advantages of using redundant checks.
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snipped-for-privacy@drexel.edu wrote: ...

...
I cannot say that the MaxSonar-EZ1 will work better in your particular application than a Sharp GPSY0A02YK IR sensor (I have not evaluated it), but only that others have used and liked the MaxSonar-EZ1 for aerial robotics. (We have had good reports when using the MaxSonar-EZ1 for aerial robots.) It was reported to us that that various sensors were evaluated and they settled on the MaxSonar-EZ1. Because of these reports we thought it would be good to get the word out.
To help save people the work of evaluating sensors, we have published a comparison of our sensor with others sensors for a simple real world test. We looked at a swinging child's basket ball with a variety of sensors (MaxSonar-EZ1, SRF04, SRF08, SRF10, and the SRF02) . This was a side by side test with the only changes being the sensors (placed in exactly the same location) and the software in the BasicAtom microcontroller. The results are here.
http://www.maxbotix.com/Performance_Data.html
The short video shows the ball swinging, and the pdf report allows easy printing and clear reading.
Regards!
Bob Gross CEO MaxBotix Inc. www.maxbotix.com
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Bob (Robot Wars Thumper 1997) wrote:

Boy, Bob, you might make a believer out of me yet. Those results are really smooth looking for your unit. I've been somewhat skeptical, having had good luck with the SRFxx's until recently, and have found problems I hadn't previously.
I just wished you had a shorter detection range. I like to use the sonars up close for manuevering and positioning. Have you thought about reverse powering the transducer very lightly to eliminate the ring down?
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear
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Bob (Robot Wars Thumper 1997) wrote:

Bob, how about adding the Polaroid (now Senscomp) data? and maybe a Sharp Ranger? to give a very good overview of the sensors available on the market.
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear
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