What's the best way to stop motion if Windows crashes?

[ctsnc]

I am using Visual Basic 6.0 to program some motion moves. I am trying to figure out the best way to stop all motion and turn off all I/Os in the event Windows crashes or stops responding. I have the following:

NI PCI-7344
NI UMI-7764
Windows 2000
Visual Basic 6.0

[absgtr]

We implemented an interlock solution using two digital lines from the PCI-7344-UMI-7764 to an Opto22 G4PB4, 4 place SSR backplane, with Brentek G4 NO and G4 NC dry contact modules wired in series to supply +24V to a larger relay contactor's coil. Also in series with the relay contactor's coil were a machine guard and machine e-stop switch.

The Relay contactor supplies 120VAC power to the servo drives and other devices on the machine.

The LabVIEW application software has to turn one bit on and the other bit off in order to power the relay contactor's coil.

We found that if the PC power is off or the PC looses power, then the contactor will drop out and kill 120VAC power to the drives.

However, if the LabVIEW application or the PC hangs then the 7344's digital
lines remain in the state that they were set before the PC hung.

To totally failsafe this also required a watchdog timer relay where the LabVIEW application has to keep
resetting the watchdog relay with a heartbeat pulse.
If the LabVIEW application fails to turn on it's heartbeat pulse then the watchdog timer relay will also
kill power to the drives.

There are probably better -simpler solutions to be applied but this worked for us.

[nestor-sg]

Another solution is using Onboard Programming. Make a LabVIEW and Onboard application in which a LabVIEW program is constantly adding one number to an Onboard Variable; an independent Onboard Program will be monitoring if this variable has change over a certain period of time, lets say 100ms, so if the variable did not change (LabVIEW crashes, OS crashes, computer locks, blue screen of death, etc.) then stop all motion and kill the axes. And since is onboard program, the computer could be locked or cycled but it will still execute.

Hope this helps.

Nestor S.