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Old July 29th, 2020, 04:40 PM   #1
alexbeatle
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Ultrasonic Distance to Wheels

Hello all,

This is an indirect PLC question.
When detecting distance to the wheels (laid flat, rims up), ultrasonic sometimes gives erroneous readings. I'm suspecting this is due to the uneven surface of the rims, but then ultrasonics have wide area scanning due to their sound cone, don't they?

Any suggestion is appreciated.

Using this sensor:
Ultrasonic UMT 30-3400-A-IUD-L5
https://www.sensopart.com/en/product...-a-iud-l5.html
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Old July 29th, 2020, 05:15 PM   #2
widelto
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Are the wheels rotating or steady. ?
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My two cents.
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Old July 29th, 2020, 05:22 PM   #3
drbitboy
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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.
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Old July 29th, 2020, 05:26 PM   #4
alexbeatle
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Quote:
Originally Posted by widelto View Post
Are the wheels rotating or steady. ?
Steady. Laying flat.
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Old July 29th, 2020, 05:34 PM   #5
alexbeatle
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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.
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.
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Old July 29th, 2020, 05:50 PM   #6
drbitboy
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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?
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Old July 29th, 2020, 06:01 PM   #7
alexbeatle
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Quote:
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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.
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Old July 29th, 2020, 06:25 PM   #8
kamenges
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Are you stuck with ultrasonic? Can you look at other technologies?

Keith
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Old July 29th, 2020, 06:28 PM   #9
drbitboy
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Quote:
Originally Posted by alexbeatle View Post
...As if particular rim orientation does not work well with the ultrasonic reflection.

loose paint on the rim?
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Old July 29th, 2020, 06:29 PM   #10
alexbeatle
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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.
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Old July 29th, 2020, 06:30 PM   #11
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loose paint on the rim?
Rims are brand new.
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Old July 29th, 2020, 07:03 PM   #12
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Quote:
Originally Posted by alexbeatle View Post
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?
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Old July 30th, 2020, 06:24 AM   #13
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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.
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Old July 30th, 2020, 06:35 AM   #14
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These would be a far better choice for measuring distance.

https://www.keyence.co.uk/products/sensor/laser/

It's our goto sensor now.
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Old July 30th, 2020, 09:00 AM   #15
drbitboy
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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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