RE: "Y" axis problem

[Kurtis Martineau <klmartineau-at-shaw.ca>]

Joe

With 585 pulse per inch, your max resolution of 1 pulse is 0.0017 inches.
Keep the  deadband set to the value :  1/585 pulses per inch = > 0.0017
inches so that EMC won't keep hunting around one pulse while holding a
position.

The backlash in you system can be compensated for by using COMP_FILE = in
your inifile - axis section.  I had to dig around alot before I found this
info in the RELEASE_NOTES in the /emc/doc file.

Probably the the real source of your following error problem is in the
tuning of the axis.  I needed to set my gain to a max of 50. I started with
10 and did a lot of trial and error style tuning.  If the gain is set too
high for your system, and you've masked the problem by setting a high max
following error limit, you will find that the motors will hunt as they move
in the commanded direction.  This will be evident by a grinding or rumbling
noise coming from the motor/drive system.  The following error created by
the poor tuning will abort the motion.

Also make sure your max velocity is set to an acceptable value for your
machine. Velocity is in inches per second, whereas axis speed is in inches
per minute.

You should research for yourself what the inifile options are and what they
do and how they do it.  I found that I made a number of false assumptions
while going through the inifile the first while.  I now have documentation
about everything there. Once all the parameters are configured then play
with the PID tuning parameters.

In a nutshell, don't just stick bandaids all over if you not sure what
you're covering up.

Better documentation for new users will evolve in time. :`)

Good luck

Kurtis


> -----Original Message-----
> From: emc-at-nist.gov [emc-at-nist.gov]On Behalf Of rehenry
> Sent: Wednesday, February 06, 2002 11:53 AM
> To: Multiple recipients of list
> Subject: Re: "Y" axis problem
>
>
>
>
> Joe
>
> I believe that I'd try reducing the acceleration a bit.  It won't really
> slow down the move that much but it will change the angle of the ramp
> that the motion stuff is using to see if the axis is where it ought to
> be.  Try 2 or 3 in there and see if that helps.
>
> Backlash from the pinion running in the rack might also cause the
> problem.  You could test this by bringing up the emc, set up an indicator
> on y and hand crank the y axis motor back and forth just until you get
> some change in the position display.  You could set this value as
> backlash but you may have a problem with homing.
>
> I'm guessing that you could also set this value of backlash as deadband.
> Set more than half the value in the ini for y axis and it should satisify
> the motion planner with a close enough for me reading.
>
> You can also attack the following error directly by multiplying the
> values for the y axis by some value.
>
> HTH
>
> Ray
>
>
>
> On Wednesday 06 February 2002 10:29 am, joe bury wrote:
> > List,
> >   I'm working on a two axis wood routing machine. It has a stg8 model 2
> > card. Each axis is driven by a rack and pinion. Each pinion is driven
> > by a series of two cog belts.
> >   I have an encoder with a resolution of 2048, but it has to travel
> > about three and a half inches to complete one revolution. This gives me
> > a resolution of about 585 per inch.
> >   On the "x" axis the encoder is coupled with the cog belt drive. This
> > axis work fine.
> >   On the "y" axis the encoder has it's own rack and pinion making it
> > more accurate as far as the Poisson of the router. My observation is
> > that emc sends the dac a signal and before the amp can ramp up and move
> > the axis enough to get some encoder counts it gets get a fowling error.
> > After that the emc releases control of the axis and there is a small
> > hop of the axis. I have hooked a meter to the dac so that I could watch
> > the signal. I have applied voltage in place of the computer to the dac
> > and the axis and encoder run smoothly.
> >   This machine was designed to move quickly three horse power on each
> > axis and with out a high degree of accuracy. I may be way off on these
> > observations but in any case I think you can get the idea of the
> > problem. I would appreciate any input on this matter,I have no idea on
> > what to try next.
> >                                               Joe
> >
> >
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