Deadband

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02 Aug 2012 13:32 #22678 by LAIR82
Deadband was created by LAIR82
I was wondering if anyone would have a calculation to establish a value for my "deadband" . I have read the section in the integrators manual and see the formula if using encoders, but we have resolvers on our machine, and i was not sure how to go about the math to establish a starting point.


Thanks

Rick

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02 Aug 2012 16:52 #22684 by andypugh
Replied by andypugh on topic Re:Deadband
LAIR82 wrote:

I was wondering if anyone would have a calculation to establish a value for my "deadband"


Is there a problem with zero?

If so, just increase it until the problem goes away.

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02 Aug 2012 17:11 #22685 by LAIR82
Replied by LAIR82 on topic Re:Deadband
Deadband sets how much either way of my commanded position it is allowed to deviate from correct?

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02 Aug 2012 20:32 #22687 by andypugh
Replied by andypugh on topic Re:Deadband
LAIR82 wrote:

Deadband sets how much either way of my commanded position it is allowed to deviate from correct?


Not quite. It sets a band around the setpoint where the controller doesn't even attempt to correct the position error.

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03 Aug 2012 03:44 #22701 by jmelson
Replied by jmelson on topic Re:Deadband
LAIR82 wrote:

I was wondering if anyone would have a calculation to establish a value for my "deadband" . I have read the section in the integrators manual and see the formula if using encoders, but we have resolvers on our machine, and i was not sure how to go about the math to establish a starting point.


Thanks

Rick

Take whatever your resolver converter produces when converted to axis units
and multiply by 1.5 for a starting value. So, if you have 4096 counts/rev and
a 5 TPI leadscrew, then your resolution is 1/(4096 * 5) = 0.0000488 inch.
So, a good starting value would be 7.32E-5
You want to keep this value as small as possible while suppressing annoying
servo dither. If it is too large, it adds a discontinuity in the servo transfer
function as it crosses zero, and can make the loop unstable.

And, of course, if you DON'T have any dither, then use zero.

Jon

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06 Aug 2012 12:40 #22902 by LAIR82
Replied by LAIR82 on topic Re:Deadband
I set it to zero and started from there going down on the count until it got "nervous" and then backed off a little bit. Nice and quiet now and no jitter on the display. The servo was humming before and I think it was "hunting" and I just did not realize what it was actually doing.


Thanks


Rick

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