Re: danger of unknown position after power down

["Pete Cook" <kf2qd-at-terraworld.net>]

Sorry about the delay but I get this mail at work and at home and at home I
am often in a more relaxed mode and more thoughts (sometimes useful) sem to
come here...

There is another problem that is related - What if the stepper motor skips
some steps - you don't know about that either.If accurate position is
necesary then you must add encoders to verify thast you really moved - In
some ways steppers are only a little better than a simulation. (snobbish
remark by dude with 3 axis servopak setting under the bench..)

Pete

> Hi Jacob
>
> With stepper motors, I think the answer would be no. To get EMC to detect
an
> amp fault (or loss of power to the stepper drives) would require the use
of
> an input pin on the parallel port. The stg drivers have this ability via
one
> of the inputs on the card. To extend this to work with the stepper driver
> wouldn't be too difficult.
> Alternatively, a N.C. relay could be wired across the E-Stop switch and
the
> coil energised by the stepper moter PSU. When the power cuts out, the
relay
> will also drop out shorting the E-Stop. Whilst EMC will go in to E-Stop,
the
> axis will still show green, so to force a homing will still require some
> coding.
> A small extension to tkemc that automatically runs a homing sequence after
> E-Stop may be one way of doing it....
>
>
> Regards, Paul.
>
>
>
> On Sunday 13 January 2002 11:01 pm, Jacob Kranendonk wrote:
>
> > If there has been a power failure or a power down on
> > the machine steppermotors, can emc detect that? After
> > power restoring the indicators stay green, even though
> > the machine is obviously at an unknown position! I
> > prefer even a obligatory axis homing before continuing
> > the cutting after such a situation occurs. Is this
> > possible? For instance I want the computer to stay
> > "on" while the machine is turned "off" and I want to
> > avoid people afterwards forgetting to home first. Or
> > else, could the EMC be set up to automaticly home
> > after each cutting job, to avoid this danger?
> >
> > regards, Jacob
>
>