Re: E.M.C. PID Tuning - HELP !!!!

good day ray,

i first have to say thanks alot for your insights and time in
assisting me. this machine has the original steppers from bridgeport
and they do not have any feedback capabilities. i just returned from
the garage with a real good feeling as i have had a good tuning
session. i have arrived at a setting of 100 for the 'p' variable and
a 5 for the 'i' variable. by adjusting these two variables in unison
i was able to use a lower 'p' value which seemed to smooth the
physical stepping characteristics of my motors at slower feedrates
while allowing them to attain greater rapid traverse velocities. in
comparison i needed a higher 'p' value to achieve the same rapid
feedrates without the 'i' value. i determined that my machine has a
backlash of .0015" and added that to the .ini file but the machine
began to wander before and after its commanded moves which i think is
a really strange situation. in order to rectify this problem i began
to experiment with the 'deadtime' variable and found that by using a
very small value '.0004' it made the wandering go away but at '.0003'
the wandering only happened once in a half hours worth of testing.
i wrote a small g-code program and had a dial indicator set up on the
test axis and began to see if the machine was missing or adding steps
as it processed the file.to my surprise there was a cumulative error
happening as the program ran i ended up having to increase the input
and output steps to a wierd value of 2008 instead of the calculated
2000, but this machine now runs and repeats flawlessly. i have read
somewhere that if the motor driver that your using expects to step at
1 and the software starts a step at 0 then this anomily may happen
but i dont know how e.m.c. operates. could you give any explainations
or suggestions on what might really be going on with this value of
2008? i must complement you and your work with e.m.c. as ive seen
your name associated with it all over the place. if it matters i am
using a microstep "gecko" drive for this retrofit project.

thanks again

jeff

--- In CAD_CAM_EDM_DRO@y..., Ray Henry <rehenry@u...> wrote:
>
> Hi Jeff
>
> Welcome to the wonderful world of tuning the EMC to a retrofit
machine.
> Perhaps I missed them but I need the answers to a few questions.
Is this a
> servo machine? Are these the stock servo drives and motors? What
are you
> using to get position feedback to the PC?
>
> Now a few thoughts. I write down the values for all of the
relevant
> variables before I make any changes. Old values get a line through
them
> and the new value below. Then make a comment on better or worse
motion as
> a result of the change. This way you can see your progress and not
worry
> much about over correction. Make only one change at a time. If
the change
> improves motion make a change in the same direction again. If the
change
> makes motion worse, step back half way.
>
> There is a tuning widget under the calibration menu but some have
reported
> that it doesn't always change the running values and save them to
the ini
> file the way that they expected. Check back to the ini file fairly
often
> with an editor so that you can make sure the values you want to
change are
> really doing it and the values that you want to remain constant are
also
> correct. Don't save from the editor while the EMC is running.
When you
> shut down the EMC, it will write final values to the ini and report
a diff
> from the old ini.
>
> I also tend to listen to motors while they start, run, and stop. A
> grinding or whining sound means to much gain. An oscillating
frequency
> while moving at a constant commanded velocity often means the gain
is to
> low.
>
> You are doing good to lower the accel rate. Do it the same for
both max
> and default. Remove the I and backlash values, double the P
value. Now
> gradually increase the acceleration until you get response near
where you
> expect them. If you get following errors, double those values as
well.
> Don't worry just yet about jerkiness as long as the machine doesn't
rock
> from foot to foot <g> or constantly trip out with following error.
>
> When you have the speed near where you want it, begin to back off
the gain
> (P) until you see some overshoot when you accel or stop and some
hunting
> during constant commanded velocity. Increase the gain a bit to
reduce this
> problem.
>
> There is nothing in the EMC quite like the older notion of gain
break but
> you can use Feed Forward to do something similar. Jon Elson
mentioned that
> he uses a FF1 value of 8.00 with his bridgeport. You could try
adding in a
> bit of this and see if it improves the motion that you have
achieved above.
>
> Be careful with (I) and (D). (D) can easily cause your machine to
run wild
> but will kick up the command when the difference between actual
velocity
> and commanded is great. (I) on the other hand will cause an axis
to lag
> behind changes in velocity because it integrates over time. (I) is
reset
> when you change direction but can be changed by compiling with a
flag.
>
> FF0 is an offset from actual position. I don't use it at all and
can't
> comment on where one might. FF2 is also a mystery to me in it's
> application.
>
> You might also remember that the motion modules and maths in the
EMC are
> intended to cover the whole range of motion including rapidly
varying loads
> and other conditions that might be encountered by vehicles. They
are not
> specifically intended for machine tool use.
>
> HTH.
>
> RayH -- U.P. Michigan
>
>
> >    From: "ja_erickson" <ja_erickson@y...>
> >
> > evening all,
> >
> > i have a few questions and oddities that have arisen during a
tuning
> > attempt of e.m.c. for my bridgeport series 2 retrofit project.
> <S>