Closing the loop with linear encoders

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03 May 2021 01:08 #207696 by PCW
1. If the step and encoder scale are commensurate, FF1 should be 1.000 by definition
2. The way so see what's going on is to "halscope" the following error and say joint velocity at the same time

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03 May 2021 14:10 #207722 by Muzzer
Thanks, will do. I had a go at looking at the joint signals yesterday but didn't manage to see it through before I got called off. I'll have a look at this next, once I've managed some more of The Big Tidy Up. The place is a tip and needs attention before I go any further.

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04 May 2021 18:31 #207858 by Muzzer
Apart from the deadband function ahead of the D operator, surely the FF1 and D functions have a very similar effect, as they are both derived from the differential of the error signal? I'm really not clear why FF1 would need to be 1.0

Bear in mind I am using position control in my system - perhaps that results in a different requirement than for a velocity loop.

I will look into this with halscope when I next get the chance. Hopefully that will give me a better idea what is going on here.

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04 May 2021 19:17 #207864 by PCW
FF1=1 because you want the velocity command (the output of the PID component)
to match the commanded velocity before any feedback need be applied

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05 May 2021 17:24 #207997 by andypugh

Muzzer wrote: Apart from the deadband function ahead of the D operator, surely the FF1 and D functions have a very similar effect, as they are both derived from the differential of the error signal?


No.

FF1 is based on the derivative of the command, D is based on the derivative of the response.

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06 May 2021 19:25 #208149 by Muzzer
Ah yes. That's rather a difference! Thanks for pointing that one out to me.

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