Re: [CAD_CAM_EDM_DRO] quick EMC question

Les Watts wrote:

> A runaway velocity mode caused by a shorted output transistor would not be a
> good thing with 1000 lb+ moving mass!

One way to deal with this (the Bridgeport way which may also be the
NFPA79 way) is to connect each of the axis drive motors to their servo
amps through a 3 pole relay. Each motor lead is connected through a set
of normally open contacts, and a normally closed contact is used to
connect (short) the motor leads together. When the machine is running
the relay is energized, the contacts that connect the motor leads to the
amp are closed, and the shorting contacts are open. When the machine
goes into e-stop, the relay is de-energized, the contacts in series with
the motor leads open, and the third set of contacts closes across the
motor leads shorting them and causing the motor to brake to a halt (this
assumes that you have regular DC brush type motors and break-before-make
relays). If a runaway condition occurs, the control will detect a
following error and go into e-stop triggering the above chain of events,
stopping all motion.

Matt