Re: servo runaway prevention

Working at GM and thoughts of encoders brought to mind a circuit that
is used to tell if a knock sensor was attached. Anyway, if voltage
read across the sensor was between 2 to 5 volts nothing happened. A
short would pull low (0 volts)and an open would go to 5 Volts. This
circuit would trigger a fault. Something along these lines could be
used to shut down power to the drives.

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
>
> > Encoder cables falling off is a really bad thing.
>
> I guess you are right that a following error would only be generated
> if the machine were commanding a move at the time the encoder
failed.
>
> It strikes me that some sort of backup 'sanity check' in the amp
> itself would be good. This might take the form of a second low-res
> encoder. If pulses are seen when command velocity is zero, error
out
> and shut down. And amp with a tach might have something to check
> consistency between the two - if one signals motion and the other
does
> not, something bad is happening.
>
> I will definitely think twice now before I go squeezeing between the
> servoed bridgeport table and the workbench it almost hits at extreme
> travel...
>
> Chris