Re: Low cost Servo Controller

> From: Jon Elson <jmelson@...>
> I don't think EMC has this (yet) but many
> CNC controls have a feature that slows all axes down if one axis starts to
> lag excessively. So, if one axis binds a little, the other axes slow

accordingly,

> or just the feed rate is stepped down to allow the slow axis to catch up.

Fred and I have had quite a few long conversations about this idea! The
discussion arose from our experience with a machine that occasionally binds
up mechanically and blows a fuse in the servo amp on the X axis, but doesn't
have AMP_FAULT outputs on the amps. By the time a following error occurs, the
part is ruined. I think, rather than modulating the feed rate in mid move,
Fred is going to scale the allowable following error to the feed rate such
that the max following error specified in the ini file is applicable to the
max velocity. At half the max velocity, the control will allow half the max
following error, etc. Of course there will be a minimum allowable following
error at low velocities to keep the control from going into e-stop
unnecessarily. This may not be quite as spiffy as what you are describing,
but it's a whole lot easier to implement. I forget what the problems were,
bit I seem to remember the phrase "reverse kinematics" coming up a lot.

Matt