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Topic: Stepper Position Sensing and Control (Read 3 times) previous topic - next topic

retrolefty

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I also started reading about steppers with position encoders built in and that got my attention since it might allow me to skip the initialization and simply drive the stepper to the correct position at any point in time.  However, I'm not finding any Arduino sketches or projects that leverage this position encoder functionality.


But there is a lot posted on using quadrature encoders which is just the input side of your stepper/encoder assembly. The problem with simple 2 channel encoders is that on power up there is no way for the encoder to tell you the specific starting point of the shaft, it just allows one to count steps up or down once you do command the stepper to move in one direction or the other. Often a design will have a optical gate at one extreme end of travel and your start-up code will move the sensor towards that direction until it detects that end of travel stop and thereafter you can just keep track of step counts to determine where you are in the full travel range.

Lefty

Tom_G_2010

I understand how hall sensors work, but don't have any hands on experience with.  I have however worked with opitcal sensors.  I'll have to look at both and see which one I can get the most precision from.

Interesting about the stepper encoders not being absolute.  Kind of a bummer actually...  Does make a simple initialize function seem like the better way to go then.

Any suggestions on motors?  Most are either 1.8 or 0.9 degree steps so I wasn't sure about accuracy on a compass display.  Can they be held between steps to get at least close 1 degree accuracy or should I be looking at a some of the more expensive 0.36 steppers?
Tom G.

retrolefty

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Interesting about the stepper encoders not being absolute.  Kind of a bummer actually...  Does make a simple initialize function seem like the better way to go then.


Well there are industrial absolute encoders available and many would be no problem to wire up to an arduino, but their price can be pretty much a sticker shock. The fact that with one external sensor and one quadrature encoder, you can emulate a absolute encoder function in software, pretty much tells you which way you should proceed. As far as optical Vs magnetic encoders that is pretty much internal details of the encoder that doesn't much concern one, it's just a matter of the electrical interface method and getting the steps per revolution resolutions you require for your application. You might note that most encoders are specified as having X number of 'steps' per shaft rotation, but with standard software encoder decoding methods you can turn that into detection of X or 2X or 4X steps per shaft rotation. So a 100 SPR rated encoder you can resolve 100 or 200 or 400 counts per revolution just by the software decoding method used to decode the A and B encoder signals.

Lefty

Erni

Did you consider a 360 degree servo ?

Tom_G_2010


Did you consider a 360 degree servo ?


I have and am ordering one to test for other applications, but have been told that absent the position feedback (which none of the 360 servos I've found have) it won't work for this application.  Am I mistaken?
Tom G.

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