Re: individual velocities

["Matt Shaver" <mshaver-at-erols.com>]

> From: Tim Goldstein <tgoldstein-at-mlh-services.com>
> The problem with setting MAX_VELOCITY to 60 is any G0 move on the Z
> axis will be implemented as a move at 60 ipm.

I know it's hokey, but you could just not do G0 moves with the Z axis. As far
as I know, G0 moves are interpolated just like feed moves in the EMC. Old
time controls could only interpolate toolpaths up to a velocity that was
usually a fraction of the speed that the axes could be driven if you weren't
concerned about what path they took. Now, with much faster computers, we can
interpolate at rates sufficient to keep up with the capability of available
axis drives (the ones available to me anyway) at resolutions typical in
machine tool control.

> Matt had mentioned that you are suppose to be able to throttle back an axis
> now (as of the Jan-2000 build) by putting a parameter in the individual
axis
> entries under MIN_OUTPUT and MAX_OUTPUT. I have tried this on my Z axis,
but
> it just seems to cause me follow errors that I can't get around.

You'll need to set FERROR to a larger value. It probably won't hurt anything
since the following error gets really large only when you command velocities
higher than your lagging axis can achieve such as during rapid moves when
(hopefully) you won't be cutting anything. Another unfortunate side effect of
using the MIN and MAX OUTPUT limits is that jogging in manual mode is a
little dicey unless you set back the feedrate override before you move. The
reason is that the commanded position gets way ahead of the actual position.
I guess that letting up on the jog button should send down a commanded
position equal to the current actual position, but that's:

1. Not implemented.
2. A feature that may have other side effects I'm not aware of.

Anyway, maybe another solution would be to specify (in the .ini file) the
velocity to use for G0 moves for each axis, and to stop interpolating G0
moves. I think Fred has this issue on his "things to do" list, but I'm not
sure what his current thinking is about how to handle this issue. As far as
acceleration goes, I don't know what amount of work on the motion system
would be required to implement per axis acceleration values.

Matt

P.S. The MIN and MAX OUTPUT limits are specified for stepper systems as
units/sec so for 24ipm, you'd have them set to + and - 0.4, and 1.0 for
60ipm. You'll want to set these for X and Y as well.