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Author Topic: 1 axis jog=smooth 2 axis jog= rough?  (Read 6501 times)

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1 axis jog=smooth 2 axis jog= rough?
« on: June 01, 2011, 02:18:23 AM »
why would x or y be smooth on there own but both rapiding together makes for a very jittery movement? it rocks the mill pretty good.(5000#)
it is only 80ipm rapid
the servos are tuned well and have plenty of power  80v  40A

i have searched but cant hit the keywords to get the results i am lookig for....

thanks

Offline Tweakie.CNC

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #1 on: June 04, 2011, 08:48:42 AM »
What do you have the Kernel Speed set at ? (Config : Ports & Pins).

Tweakie.
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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #2 on: June 04, 2011, 11:59:03 AM »
100k
does it sound like the computer wont keep up with that many pulses?

Offline Tweakie.CNC

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #3 on: June 04, 2011, 12:26:07 PM »
I suggest that you try changing the Kernel Speed to 25k, restarting Mach and retuning your velocity settings for maximum reliable motor speed and save these settings.

100k is really not the best setting for performance and, depending on steps per, it is unlikely that it is ever necessary to exceed the 35k Kernel Speed.

Tweakie.
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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #4 on: June 04, 2011, 10:11:49 PM »
well, i am going 1024 on the encoder, 4-1 on the pulley ratio, and .200" screws.  80 ipm rapids
i think it was like 92k or something on the motor tuning.....

Offline BR549

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #5 on: June 04, 2011, 10:43:31 PM »
I would change out the encoder to about 1/4 of that. No way can you use that much resolution.  128 encoders would give you less than 1 ten thousand  inch resolution .00009".

Let's be resonable, (;-0 TP


Offline Hood

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #6 on: June 05, 2011, 08:50:01 AM »
I would change out the encoder to about 1/4 of that. No way can you use that much resolution.

Have to disagree there, the more resolution you have the better as it should allow much better tuning on a servo system but thats just my opinion ;)

But with high count encoders and the parallel port it can be a problem as you need to run a high kernel and not many will reliably run at over 65KHz. Using an external controller such as SmoothStepper, KFlop etc does away with that issue.
See if your drives can utilise electronic gearing, personally I am not a fan of it but at least you would be able to reduce your kernel without having to change out encoders.

Hood

Offline BR549

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #7 on: June 05, 2011, 10:31:02 AM »
At better than 81000 PPI you are long past the point of diminished returns on resolution. Take a look at the resolution of high end commercial machines you won't find many if any that high.

Remember this machine has 20x reduction on the servo. If you don't want to change the encoders then change the 4:1 to 2:1 reduction or 1:1
(;-) TP




« Last Edit: June 05, 2011, 10:38:54 AM by BR549 »

Offline Hood

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #8 on: June 05, 2011, 10:40:01 AM »
Terry I am meaning resolution between drive and motor and most industrial servos with encoders that I have seen have at least 2000 counts per rev, some, such as the MPL motors I use on my  spindles, which have smart encoders, can have as much as 1million lines per rev if required (I just have them set to 4096) .

Hood

see you have edited ;) that is why I mentioned electronic gearing, gives lower resolution between Mach and drive(axis movement) but still keeps the same between encoder and drive.
« Last Edit: June 05, 2011, 10:47:14 AM by Hood »

Offline BR549

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Re: 1 axis jog=smooth 2 axis jog= rough?
« Reply #9 on: June 05, 2011, 11:35:18 AM »
YES I agree that electronic gearing can work BUT you still end up with micro cogging you try toget rid of with high encoder counts (;-) The gearing just uses blocks of pulses instead of one.

YEP here I run 2000 count encoders and end up at 40000 PPI and that is WAY more than is needed to have smooth motion, high resolution @ .000025" ( way more than this ole Bridgeport can use) and 100 IPM rapids.

Just a thought. (;-) TP