EMC minor quirk

[Jon Elson <jmelson-at-artsci.wustl.edu>]

This is one for Fred Proctor or Will Shackleford;

When EMC is moving in a rounded-off rectangular
path of alternating linear and arc moves, with cutter
diameter compensation turned on, I noticed that at the
end of each straight line, the machine would accelerate
monentarily, before starting into the arc move.
It is not serious, but seems like there is a quirk in the
calculation of velocity on the offset path to get the
desired velocity on the actual cutting line at the perimeter
of the tool.  Since the velocities on the linear parts
are the same (offset and actual) it must have something
to do with the calculation for the offset velocity for the
arc.  But, the arc seems to be done right, it may be the
software is wrongly calculating arc velocity when it
attempts to match velocity at the end of the line with
the beginning of the arc.  This is the best that I can
interpret the behavior.  If a stepper system will exhibit
this same behavior, the audible steps might be very
obvious.  It is a little less obvious with servos, but
I can clearly detect the accelerations.  The RS-274
program has all of this movement programmed at a
constant speed of 10 IPM.  The tool is set to a
diameter of 0.5".

My setup is using the 20-DEC-1999 EMC, with
servos driven by the Servo-to-Go card.

This is not a serious problem, but if I have guessed
the origin of the problem correctly (a long shot) then
it might get more serious the larger the tool diameter
is set to.  There is no evidence of this speed variation
when cutter diameter compensation is not active.

Thanks,

Jon