Omron Rotary encoders - stepper motors.

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31 Aug 2017 02:17 #98252 by jmelson
jmelson replied the topic: Omron Rotary encoders - stepper motors.

andypugh wrote:
It _might_ be possible to connect the pid error value to the adaptive feed pin so that step-rate reduces while still making up the lost steps, but I don't know if anyone has ever tried it.

My Allen-Bradley 7320 had this feature, but it did not have a smooth on/off logic. When the feedrate caused increasing error, the machine jerked to 1/2 the feedrate, the motors caught up, and the cycle repeated. I had to disable it to prevent tipping the mill over.

Jon
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31 Aug 2017 10:10 #98274 by Moronicsmurf
Moronicsmurf replied the topic: Omron Rotary encoders - stepper motors.
@andypugh i wonder how those "closed loop stepper motors" drivers deal with this then, they are basicly a rotary encoder with a closed loop in its own.. if it would counteract the purpose of it, it would just end up being an interesting experiment i guess..
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31 Aug 2017 10:20 #98275 by andypugh
andypugh replied the topic: Omron Rotary encoders - stepper motors.

Moronicsmurf wrote: @andypugh i wonder how those "closed loop stepper motors" drivers deal with this then


They run like a very high pole-count brushless motor. I think that they also have a torque reserve, the driver is allowed to temporarily over-current as it "knows" what is going on.
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31 Aug 2017 13:24 #98286 by Moronicsmurf
Moronicsmurf replied the topic: Omron Rotary encoders - stepper motors.
of course that makes sense.. hmm.. Wonder if one could "copy" that behavior within linuxcnc tho.. but some form of "measuring" needs to be performed then.
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31 Aug 2017 15:03 #98293 by Todd Zuercher
Todd Zuercher replied the topic: Omron Rotary encoders - stepper motors.
Theoretically yes, practically I'm not so sure. Biggest limitation might be timing resolution and granularity (a 1kHz servo thread likely isn't going to be fast enough.)

I've wondered if a high resolution encoder couldn't help with improving the accuracy of a high microsteoped stepper (32x microstepping or so) and limit max following error to something less than 1 full step.
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