New .ini entries, [AXIS_#] DEADBAND, MAX_VELOCITY

[Fred Proctor <proctor-at-cme.nist.gov>]

EMC users,

The 29-Feb-2000 distribution introduces two new .ini file variables in
the [AXIS_#] sections, DEADBAND and MAX_VELOCITY. You'll need to add
these to your .ini file; see generic.ini for an example.

	[AXIS_#] DEADBAND = <non-negative float>

sets the error tolerance between commanded and actual position, below
which the error is set to zero. This is intended to prevent hunting
about a pulse. The default is 0.0, meaning it has no effect and any
error will drive the PID a bit.

The EMC now generates positions rounded to the nearest input step,
either encoder count or stepper motor count. So, hunting should not be a
problem. It can kill small oscillations due to agressive servo
parameters.

The other .ini file addition,

	[AXIS_#] MAX_VELOCITY = <positive float>

sets the rapid rate for each axis, independently. I tested this briefly
and it worked for me, but please test this and report any problems. It's
intended to allow you to set a smaller value for the rapid rate for your
lowest-performing axes, so that if they are not moving during a rapid
move the other axes can move at a faster rate.

For example, if you have a Z axis that can only rapid at 20 ipm (=0.333 
inches per second), and your X and Y axes can rapid at 120 ipm (=2.0
inches per second), you should do:

[AXIS_0]
MAX_VELOCITY = 2.0

[AXIS_1]
MAX_VELOCITY = 2.0

[AXIS_2]
MAX_VELOCITY = 0.333

If X and Y move equal distances during a rapid, their rate will be 120
ipm each, and the effective tool tip rate will be sqrt(120*120 +
120*120) ipm, or 168 ipm. If Y moves a shorter distance, it will be
slowed to arrive when X arrives, but the overall time for the move is
the same as if they both went at 120 ipm. At this point it's more
difficult, believe it or not, to have them move independently at their
rapid rates and arrive at different times.

The way this is done is by computing the time each axis would take if it
moved the prescribed distance at its own rapid rate, then taking the
longest time, computing the equivalent tool tip rapid rate for the total
tool tip distance for this time, and doing a linear move at that rate.

The existing .ini parameter, [TRAJ] MAX_VELOCITY, is used to limit the
overall tool tip velocity. Make it twice the max axis rapid and your
axes will always run their fastest.

--Fred