Magnetic Rotary Position Sensors

Workshopshed over 12 years ago

I'm hoping to evaluate the AS5048B sensor for a rotary table solution.

http://www.ams.com/eng/Products/Magnetic-Position-Sensors/Rotary-Magnetic-Position-Sensors/AS5048B

There's a bullet point on the description that reads:

"Angle accuracy 0.05°after system linearization and averaging"

I understand about averaging but what is mean by system linearization and how would I go about doing that?

Has anyone used this model or others in the series? Product LinkProduct Link

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Workshopshed over 12 years ago in reply to Workshopshed +1

Bit more progress on the test rig http://www.workshopshed.com/2013/06/magnetic-sensor-test-rig.html

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vsluiter over 12 years ago

Hello Andy,

I haven't used these sensors, but what is meant by linearisation is that you turn the object whose rotation you're trying to measure one full revolution while measuring the rotation with another device (higher accuracy absolute position encoder, or use a transmission to measure revolutions on another axis).
Ideally, every LSB of the output is exactly 360/(2^14) degrees. Due to sensor errors, or misplacement of your magnet it could be that in one place the LSB size is a bit larger than in other places, giving 360 degrees as a sum of all bits, but differing a little over the rotation (read in on INL and DNL on Wikipedia)
To linearize, you'd need to map the true rotary position to the measured rotary position, for example using look up tables.
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Workshopshed over 12 years ago in reply to vsluiter

Victor,
thanks for the clarification that seems straight forward enough. I'll have to work out how I might go about getting more accurate positioning/measurement. The joy of having a microcontroller in the mix is that I can upload new firmware so to speak late in the project.

Hopefully my primitive test rig will be sufficient to test out the electronics and software, I was a bit limited on non magnetic materials so wood and plastic had to do.

Cheers,
Andy
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Workshopshed over 12 years ago in reply to Workshopshed

Bit more progress on the test rig

http://www.workshopshed.com/2013/06/magnetic-sensor-test-rig.html
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vsluiter over 12 years ago in reply to Workshopshed

Would using a metal rig be that bad? I'd guess that linearizing / field mapping would remove the problems you'd get from that. Will you be moving to metal later on? I'm curious what the effects would be.
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vsluiter over 12 years ago in reply to Workshopshed

Would using a metal rig be that bad? I'd guess that linearizing / field mapping would remove the problems you'd get from that. Will you be moving to metal later on? I'm curious what the effects would be.
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Workshopshed over 12 years ago in reply to vsluiter

I will be moving to metal, the table that I plan to attach this to will be mostly aluminium with a steel spindle.

I don't plan to rotate the table quickly, so the averaging is not too much of an issue. One thing I did realise just yesterday is that I need to be careful about the averaging and crossing zero. So I'll factor that into the algorithm.

I've see the Renishaw chips before but not the IC-Haus ones, thanks for the links.
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