RE: Runaway z axis with steppers

[wb9mjn <wb9mjn-at-wb9mjn-11.ampr.org>]

  Hi Ray,

        Yes, I have this problem too on a BDI/TNG implementation. But it is 
on my Y axis. Setting the P to 1500 minimized (eliminated?) it for MDI and 
AUTO commands. But it still happens after the first or second manual 
command to the Y axis.

      73, Don...


-----Original Message-----
From:	Ray Henry [SMTP:rehenry-at-up.net]
Sent:	Saturday, September 07, 2002 11:26 AM
To:	Multiple recipients of list
Subject:	Runaway z axis with steppers


EMC List

I posted this a while back to the developers list at sourceforge but I
don't think that that list is working so I'll post it here.

Attached is an ini from Tim <tim.smith-at-electrolux.com.au> that does some
goofy stuff here.  I'm not exactly going to call it a bug, rather the odd
behavior is the product of certain combinations of values in the ini file
when used with freqmod.o.  The same behaviors are not obvious with
steppermod.

I'm started testing this with TNG with no machine attached to the
parport. I think I'd be afraid to start much of a machine with this setup
because it trips up the stepper math and creates an oscillator that tends
to push an axis slowly in a single direction -- even when no motion is
commanded.  With the attached ini file, I see this behavior after a
couple of quick jogs of the Z axis.  

I've also tested this behavior with BDI-2.16 and my Grizzly minimill and
it seems to behave the same as the TNG.

Here is what I did to exhibit the problem.  

Startup using timsfreq.ini.  (attached)
Start the machine and home out.
Start scripts->IO_Exercise to view parport 0x378. (default)
Issue a couple of quick jogs in Z

Once the problem shows up with the IO_Exercise display and I press estop,
the step pin seems to latch but the displayed position runs wild.

The problem seems to go away if scale is set about 20 with a proper
deadband.  It also goes away or changes the way it works with larger
gains and different combinations of velocities and accelerations.

With some small adjustments, the problems seems to change into a simple
dither between adjacent steps but as it is, all of the steps are in the
same direction.

I need someone to see if they can reproduce this problem and work with me
to clearly define the nature of it.

Ray



 << File: timsfreq.ini >>