Ultrasonic Distance to Wheels

alexbeatle

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Feb 2010
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San Francisco
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How far are any other surfaces? the technical specifications show the sound cone with a diameter of 1m around 1.6m out and 1.6m around 3m out.
 
How far are any other surfaces? the technical specifications show the sound cone with a diameter of 1m around 1.6m out and 1.6m around 3m out.

Good point.
I'm working in the range of 530mm…1950mm away from the sensor.
There's a metal frame within 300mm from the cone centre.
 
can you cover that frame with something that might absorb the ultrasound e.g. a rag or fiberglass insulation as a test, to see if the erroneous readings are still there?
 
can you cover that frame with something that might absorb the ultrasound e.g. a rag or fiberglass insulation as a test, to see if the erroneous readings are still there?

Just tried, no change.
The fluctuation does go away if I rotate the rim. As if particular rim orientation does not work well with the ultrasonic reflection.
 
Are you stuck with ultrasonic? Can you look at other technologies?

Keith

I may move away from ultrasonic.
Could you please recommend an alternative?

Ultrasonics are simple to implement and have a cone signal - 2D scan area. Laser distance sensors have a point signal and may shine through the rims, depending on the orientations of the whole pattern. So need a 2D distance measurement to give analogue output.
 
Just tried, no change.
The fluctuation does go away if I rotate the rim. As if particular rim orientation does not work well with the ultrasonic reflection.


I suspect you're getting false echoes that bounce around inside the wheel prior to being reflected back to the transducer. I've had that problem with enclosed vessels sometimes when using ultrasonics. Seems that laser would be a better choice, but I understand that it would miss the presence of the wheel were it aimed at a hole in the wheel. Perhaps a capacitive distance sensor would work?
 
There are many brands of ultrasonic, with different characteristics. Some have a narrow beam like this one from baumer.
baumer ultrasonic.png
If it's not possible to move the sensor closer to the rim, you could try a waveguide to focus the beam closer to where you want to measure.
 
Can you take a picture of, or sketch, the geometry?


E.g. is the sensor looking down at the side of the rim or horizontally at the full width of the rim, or at some angle? Is the side of the wheel flat or is it like a car's wheel, with rolls and holes?


What are the dimensions of the wheel, and what is the nature of the erroneous values (bigger, smaller, always around Xmm different, etc.)?
 

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