Electronics > Projects, Designs, and Technical Stuff
Rotary encoder accuracy - mine doesn't seem very good
Corporate666:
--- Quote from: Peabody on March 06, 2019, 03:22:58 pm ---Seems unlikely that an optical encoder would vary that much. Does the +/-15% cycle coincide with one encoder revolution?
--- End quote ---
The variance repeats... in other words, it's over in the same position of revolution each time and under in the same position of revolution and it generally smoothly transitions from the min to the max and back. That's what makes me think it's a manufacturing issue.
Corporate666:
--- Quote from: retrolefty on March 06, 2019, 12:15:42 pm ---Looking at the details of the listing for that encoder I see that it has open collector NPN A & B output pins. Are you to supplying proper pull-ups for these signals to operate properly?
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Yep, I'm using pull-ups.
ataradov:
Those encoders use transparent plastic disc and a couple of optical pairs, and offset of that disc from the axis would produce this behavior.
Corporate666:
--- Quote from: OM222O on March 06, 2019, 11:37:17 am ---Can you provide the code/oscilloscope trace which you used to measure the speed? I've used cheapie ones without much of an issue tbh.
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I didn't save it but I just probed the encoder outputs in-circuit to see why I was getting such a variance in my reading, so there wasn't code involved as such. I am seeing the quadrature output and the square wave looks perfect. It's simply that the period and duty cycle/pulse width change over the course of a revolution, despite the encoder shaft being turned at a precise rate.
I picked up a few more encoders and will see if they do the same or if this might be a bad unit.
IconicPCB:
How will this cyclic error show up once the quadrature signals are decoded?
As for speed, use a tacho these are used as positional sensors primarily.
If used to synthesise a tacho signal... apply a bit more averaging and you wont notice it.
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