Re: Using DRO data for feedback for a stepper drive

["William Scalione" <wscalione-at-nc.rr.com>]

EMC will handle encoder feedback on a stepper system, but it
needs a plug in card, sold by Camtronics, and designed by Tom
Kluga (spelling?) Under $100.00 I think. The problem with this
is, if an axis is lagging due to a stalled stepper motor, or one 
missing steps the controller tries to increase the step count to
make up the difference. But that will not do anything except
make it worse. But there are people doing it here so it may
work ok on a properly designed system. Don't know of anyone
doing it with the parallel port. Also encoders are usually run
in quadrature which requires 2 wires plus 2 grounds although
I suppose you could just leave one pair off, cutting the resolution
of the encoder by 4

Bill

> 
> Here is a topic that I have not seen discussed in much detail.
> 
> It seems to me that if one were to use the signal from a DRO sensor
> such as an Accu-Rite to give table position to feedback to the
> controller, the controller then could correct for error just like in
> a servo setup.  Thus, any error due to drive belt error, backlash
> (which can vary with table position) would automatically be
> compensated, resulting in increased accuracy.
> 
> Since the limit switch setup for EMC gangs the three axes, together
> you have 2 signals for  the + and - limits. If you forgo home
> switches and assuming that the sensor would be simply a serial pulse
> train, putting out a pulse for each table increment, there would be
> three more wires for axis data for a total of five inputs that a
> parallel port can accommodate.
> 
> Does anyone have a setup like this, is it possible with EMC or am I
> just dreaming?
> 
> Jack Ensor
> 
>