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Real time for what?Real time for what?Posted Nov 13, 2012 21:48 UTC (Tue) by dlang (✭ supporter ✭, #313)In reply to: Real time for what? by man_ls Parent article: LCE: Realtime, present and future
> Cool! Those look pretty critical to me: having catastrophic consequences if they fail -- at least causing damage to property, and probably to operators.
I have built a CNC machine, so I have first-hand experience here.
It depends how the system fails.
If they fail by not scheduling for 100ms (or even 1s), there is probably no problem besides delaying the work.
If they fail by sending the wrong commands out to the equipment, things can be worse.
But these do not require real-time scheduling to operate.
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Real time for what? Posted Nov 13, 2012 22:36 UTC (Tue) by man_ls (subscriber, #15091) [Link] I was thinking more along the lines of plasma cutters or robots, also mentioned in the link: failing to switch off the plasma may have bad consequences. Or a cutting machine which needs precise synchronization between different pieces. But perhaps most of these machines are designed to be fail-safe.
Real time for what? Posted Nov 13, 2012 22:58 UTC (Tue) by dlang (✭ supporter ✭, #313) [Link]
failing to shut off the plasma cutter has very little effect (other than possibly a small amount of damage to the piece being cut), if you go off the edge, the plasma isn't going to be sustained, if you leave the cutter in place, the plasma will eat a small amount around the location until the circuit can't be sustained any longer and the plasma will cut off.
These things rely far less on precise timing than you think.
Just about all of the DIY devices rely on stepper motors, which move a specific distance when pulsed, not normal motors run for a specific amount of time.
If the pulses are late, things move a little slower. If there is enough momentum in the system, it's possible for that momentum to cause the equivalent of 'jumping a tooth on a gear' and being slightly out of position, the solution to this problem is to slow the machine down a bit.
synchronization between different pieces is a matter of either moving one motor, then a different motor, then the first one again, or in setting up the movement for both motors and sending a 'move now' pulse. In either case, slight delays don't break anything.
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