Machine
vision systems need to communicate with sensors and motion control
devices. Usually a PLC manages moving the object to be inspected in
front of the camera, listening to sensors and talking to the motion
controller as necessary.
Sometimes
though, there is no PLC. I’ve seen number of situations where
machine vision had to be installed on an antiquated line that still
used relays. When that happens there’s no option but to ask the PC
to track parts and talk to drives.
But
there are advantages to doing everything on a PC. Put simply, you can
use whatever software you want, rather than being tied to ladder
logic and whatever protocols a vendor provides.
That’s
the argument adopted in “Deterministic
Motion Required”
published on the Control Design website, September 11th,
2013. Now this lengthy article describes a situation where aging
machine tools were being upgraded, but I think the points are just as
valid for a vision application. Don’t just assume a PLC is the best
way to do it.
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