Re: ready to start up EMC

[rehenry <rehenry-at-up.net>]

On Saturday 02 March 2002 10:24 am, Les Watts wrote:
> Well, the big gantry mill is ready for EMC!
>
> Servo to go II is in and reading encoders, switches, etc
> and outputing from the DACs with the dos based test program
> from stg.
>
> This system has a hardwired e-stop so will not use emc for
> that function.
>
> I am using the latest bdi.
> A minor logout problem is the only glitch I saw. No big
> deal.

Good.  Congrats on getting this far!  You have become an adventurer on 
the digital frontier.

> I have a few questions though. I want to know what to expect
> as I power this up. It will be moving 1000 lb ! I will of course
> use a reduced servo voltage at first and just rough tuned
> pid. And be on one of the estop switches!
>
> 1) when does the homing sequence start? How does emc
> know which way to go?  Does it bounce the home switch
> and reverse or pick up the first index pulse past it? My home
> switches are at one end of each axis just before the limit
> switch.

I'd first set up the motors and amps so that you can power them up and 
not have significant movement.  If these are analog(ue) amps there will 
be gain and bias or null, or some such pots on them.  Crank the axes away 
from the ends and power up an axis with a jumper shorting across the 
analog in.  Adjust bias until there is very little motion.  Repeat for 
the others

I noticed that with my STG here that there was a very small offset when 
the board was idling.  You can approach zero with this when the axis is 
connected by setting a little bias in the ini for that axis.  Again the 
idea here is to minimize motion when the stg and axis are powered up but 
not running with a closed motion loop.

Next thing to do is see which way the axis displays count when you move 
one.  If it is the correct direction great.  If not change the + or - in 
front of the output scale for that axis and try again.  When you get 
these correct for your machine model you are ready for closed loop.

Power up your machine and Press estop <F1> in the EMC and turn the 
machine on <F2>. and all heck should break loose.  Keep your finger on 
the real e stop that kills axis power.  Here you may need to change the 
polarity of the analog(ue) signal from the stg to the drive amp if an 
axis starts to go wild.  You might also be able to put a minus in front 
of the max output and a + in front of the min but I haven't tried it.

Now you are ready to set manual jog polarity so that you get the 
direction of motion that you expect when you press plus or minus.  This 
is also done in the ini by one or zero in that variable.

Now that you have some control over your machine, you can begin to tune 
each axis so that you get smooth acceleration and deceleration.  I would 
begin by setting the accel to a very low value like 1 or 2 and then 
gradually raise it while you adjust gain for smooth motion.  

Gain is tricky and there are some pages in the handbook that can help you 
understand it.  When you get gain close, with your very heavy gantry you 
may need to put it a little bit of I and D.  Jon E. swears by ff1 and 
says that it is a good way to anticipate changes in speed.  I believe 
that he uses the value 8 in his bridgeport.

What I try for here is a nice sound from the motor.  Once you get 
reasonably smooth motion to the eye or hand, then begin to listen to the 
motors when you command a rather long motion at slow speed.  You should 
hear a nice even hum.  If you hear hunting or a varying frequency then 
you need to increase the value of gain.  If you hear a growl you need to 
reduce it.   Try this at several speeds.  A stethoscope, plastic cup, 
socket extension or pipe or bar between the motor and your ear can help 
you hear what is going on.

> 2) which EMC version (on the bdi) should I use for a three axis
> machine? I have only run the simulated one so far.

This isn't critical since you are revising the ini.  What you need to do 
is make sure that the run file that you use is pointing to the ini file 
that you are editing.  I've made this mistake more than once.

> I am getting the .ini file together; it looks pretty straightforward. I
> may have some questions about cycle times.

Hope this helps.  Good luck and may the EMF be with you.

Ray