In conversation with a supplier of motion control products for EMC and Mach3 
the discussion of PID loops arose.  The discussion was in the context of servo 
driven systems.

Here is some information that I would welcome others review and comment.  There 
are no flames in the following and there is not intent to start any flaming.  
An apples to apples comparison is being sought.

A system has to be chosen for to retrofit a mill that will be cutting 3D 
surfaces.  Curve intersecting curve intersecting flat on an angle, etc.  I have 
retrofit similar mills with Centroid systems and the users regularly program at 
100 ipm and observe that the mills average about 60 ipm (as low as 10 - 15 ipm 
in very curvy detail or tight corners and up to 95 ipm on almost flat curves 
and wide open corners).  Does anyone have experience with EMC or Mach3 
achieving the same level of performance as the Centroid system?  If yes, what 
configuration was used?

For emc, the PID loops are in the PC software, for Mach3, the PID loops are in 
the motion control hardware.

EMC's PID loop has a cycle rate of 1000 times per second.  Is this a fact?  If 
yes, are there any options to get the PID loop to run faster?  There is motion 
control hardware available for Mach3 that is capable of a PID loop with a cycle 
rate of 5000 times per second.


Although EMC receives feedback in realtime it does not adjust commands to the 
axes if the axes are getting closer to exceeding the following error limits.  I 
do not know this to be true.  This is a statement from the supplier of motion 
control hardware for EMC and Mach3.

Mach3 is an open loop system sending commands that are managed by the motion 
control hardware which will shut down if the following error limits are 
exceeded and then tell the Mach3 system that it has shut down.

I look forward to replies.

Have a good day,

Jim
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