joint 2 following error

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30 Nov 2013 04:24 #41228 by garymcrobertpdx
Strangly the axis following error problem has returned even
though I have not changed any configuation values.

I serched the the ini and hal files for the Base period value
but did not find it.

Is this because I am using a Mesa 5i25 board and the
the base thread rate is not avalable in the ini or hal files?

I do remeber seeing in the Pncconf wizard setup a thread
period input value. Is this the base thread rate?

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30 Nov 2013 04:36 #41229 by PCW
Replied by PCW on topic joint 2 following error
A base thread is not needed (or wanted) for the hardware stepgen.

Are the following errors during rigid tapping as before or just normal motion?

Did you fix the huge dir setup and hold times? (they were 200 uSec which has to be wrong)

Have you changed anything that would add more latency? (re-running the latency test might be a good idea)

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30 Nov 2013 04:59 #41230 by garymcrobertpdx
The Compumotor S6 drive input specs are:
A minimum step pulse width of 200 ns at a 40% - 60% duty cycle.

The Dir spec states that the direction must be stable for 2 miliseconds
before the drive receives the first step pulse.

This dose seem like a long time perhaps this is a typo and they
ment ns not ms!

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30 Nov 2013 07:28 #41233 by garymcrobertpdx
Assuming that the 2ms is a typo and it should have been 200ns
I have experimented by changed on XYZ&B axis the ini vars to.
dirsetup = 400
dirhold =400
steplen = 400
stepspace = 400

The drives seem to work OK with this since the homing process
appers to work correctly. How ever when I exicute a G2 to bore
a 0.312" hole I get the same axis 0 following error as before.

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30 Nov 2013 09:20 #41236 by PCW
Replied by PCW on topic joint 2 following error
Did you check your latency?
poor latency can cause following errors.
Unfortunately the current driver is more sensitive
to latency than it should be.

Also you have (at least) 8 step generators enabled
are this many actually used?
Enabling more hardware than you need will make
the latency caused ferror more likely to happen

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30 Nov 2013 10:26 #41237 by garymcrobertpdx
Yes checked the latency again, I get a base thread of 25709 ns
and a servo thread 26654 ns This is the same as it has been.

I am using a Mesa 5i25 and a 7i76 daughter board since I need six
stepgens I have selected the 7i76x2 firmware option this yeilds 10
stepgens.

I see them in the hal file loadrt hm2_pci config " stepgens=10"
due to hardware consiterations I am usnig stepgens 04 to 09
00 to 03 are not used. Is there a way to disable these with out
affecting the stepgens I am using

One other observation If I set the feed rate very slow 1.5 in/min the
G2 boring of the 0.312" hole with a 0.250 endmill works but at 15 in/min
fails. How ever when I use the 0.125 endmill to G2 bore a different hole
0.280" it works fine at 15 - 20 in/min feed

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30 Nov 2013 10:45 #41239 by PCW
Replied by PCW on topic joint 2 following error
The driver has no way to select individual stepgens
so you do have 10 enabled which is likely part of the problem

I would try re-arranging your wiring so that you can get by with just 6 stepgens enabled
(even is this requires somewhat different firmware)

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30 Nov 2013 11:47 #41240 by garymcrobertpdx
Is it possible to disable the upper 4 stepgens by modifying the hal file to
loadrt hm2_pci config " stepgens=6"

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30 Nov 2013 22:01 #41259 by andypugh
Replied by andypugh on topic joint 2 following error

Is it possible to disable the upper 4 stepgens by modifying the hal file to
loadrt hm2_pci config " stepgens=6"


You can have zero or more stepgens, but the ones you get always start at the lowest index number. So you can have 0,1,2,3,4,5 with the right stuff in the config string, but not 4,5,6,7,8,9.

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27 Dec 2013 00:23 #42033 by PCW
Replied by PCW on topic joint 2 following error
I have done some experimentation and have found that you can get better
stepgen following performance on systems with moderate jitter by using a
PID loop for position control instead of the stepgen drivers built-in position control loop.
The problem with the built in driver position control is that its tends to overcorrect
for measured position errors cause by sampling jitter.

Here is an example hal /ini file setup:

freeby.mesanet.com/hm2-pidstepper.zip

For PID control of the stepgen, the stepgen is put into velocity mode and a basic velocity mode PID setting is used (FF1 = 1.000, FF2 = .001 (servo period) P= ~150)

This seems to work well for Ethernet systems which have large jitter (>100 usec)
The following user(s) said Thank You: zu4lu

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