Mesa 7i77 and linear encoder tuning PID.

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15 Aug 2012 13:09 #23239 by andypugh
ROG wrote:

www.f1-2000.co.uk/index.php?f=hardinge_hxl2
You’ll understand my woe with regard to changing motors!


Absolutely! (and very nice work too)

I guess as a last resort I could pop up with some 8i20 drives to try.

But it really ought to be possible to minimise the Omrons into controllability.

You might end up with two PID loops in HAL, one running the drive/motor under encoder feedback, and a second one (probably slow and I-only) tweaking that one from the linear scale feedback.

But I would certainly support the suggestion I think I saw earlier of running both LinuxCNC and the drives from the same encoder initially.

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15 Aug 2012 13:36 #23241 by ROG
Cheers Andy .... its been more work than I ever imaged.
Every corner you turn seems to be 10 times more difficult than you possibly imagined.
This should now be the enjoyable bit, now most of the mechanical hard work is done, getting the machine setup and the making all the nice tactile bits for the control etc.

Do you and your 8i20 s fancy a little holiday in Norfolk then? :)

It’s been worrying me that if I change the drives, what to ... how much.... will that cure the problem....

I haven’t had a chance to get the motor encoder cable made up yet, that’s on the cards for tonight.
So I’ll report back findings from there.

As I said before, this is all virgin territory for me, so please bear with me as I’m still pretty clueless.
That said, for me, my gut instinct from the first time i starting doing battle, was the drives may be the problem.
“You might end up with two PID loops in HAL, one running the drive/motor under encoder feedback, and a second one (probably slow and I-only) tweaking that one from the linear scale feedback.”

Is that available as a “cut and paste” ;)

This may be a stupid suggestion, but what would happen if:
setp hm2_5i25.0.encoder.00.scale 25600... (25600 linear encoder)
setp hm2_5i25.0.encoder.05.scale 8192 ... (8192 output from drive)
then

net x-pos-fb <= hm2_5i25.0.encoder.00.position
net x-vel-fb <= hm2_5i25.0.encoder.05.velocity

or something along those lines ?

I composing an email to Omron, to see if they can shed any light ......

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15 Aug 2012 13:44 #23243 by andypugh
ROG wrote:

Is that available as a “cut and paste” ;)

Probably not, though it shouldn't be any more difficult than a single PID really.

This may be a stupid suggestion, but what would happen if:
setp hm2_5i25.0.encoder.00.scale 25600... (25600 linear encoder)
setp hm2_5i25.0.encoder.05.scale 8192 ... (8192 output from drive)
then
net x-pos-fb <= hm2_5i25.0.encoder.00.position
net x-vel-fb <= hm2_5i25.0.encoder.05.velocity

That sort of thing ought to work fine, though I don't think LinuxCNC would do anything useful with that x-vel-fb so isn't the answer you are looking for.

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15 Aug 2012 14:26 #23245 by ROG
Probably not, though it shouldn't be any more difficult than a single PID really.

if .... you know what your'e doing!

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16 Aug 2012 15:08 #23295 by ROG
Further developments...


Encoder output from drive / motor connected to 7i77 as encoder 2 for vel / pos feedback

Linear encoder left connected as encoder 0


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16 Aug 2012 15:12 #23296 by ROG
I’ve also changed the belt and added more tension by this point.
Looks like some of the delay is before the motor / drive responds and the rest mechanical?


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16 Aug 2012 17:52 #23301 by ROG
Motor off in e-stop – wrench tuning ball screw mild acceleration – red motor encoder – blue linear encoder

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16 Aug 2012 17:53 #23302 by ROG
Motor off in e-stop – wrench tuning ball screw mild acceleration – red motor encoder – blue linear encoder

zoom1

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16 Aug 2012 17:54 #23303 by ROG
Motor off in e-stop – wrench tuning ball screw mild acceleration – red motor encoder – blue linear encoder

zomm 2

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16 Aug 2012 17:55 #23304 by ROG
Motor off in e-stop – wrench tuning ball screw harsh acceleration – red motor encoder – blue linear encoder


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