I've worked on a handful of cells in the past, but I'm designing a new one now and I want to address the problems we've had on the other implementations:
Our first problem was that routing I/O through the arm / dresspak is a pain. We addressed this by running only three lines to the tool: Air, Ethernet, and Power. Then add Ethernet-based IO blocks and valves locally to the tools. We also abstract all the IO. The PLC communicates directly with the EOAT's I/O, and passes it to the robot.
But now the issue is when do I cut the air and power to the valve bank?
Part of me want to dump air anytime the fence is opened. The other part of me knows that this means maintenance tasks cannot occur. So, I have to leave power and air on the tool, even when the fence is opened.
This unfortunately means that there is a possibility (through poor coding or device failure) that the EOAT can move while a person is within the fence (unless I equip the EOAT with CIP-safety modules, which I would like to avoid).
How does everyone else handle this?
At the moment, I'm looking at using an IO-Link Master on the tooling. There will be a lockout point that cuts the actuator power to that module (Mini 7/8" port, pin 1), which will disable all the motion.
I'd leave that actuator power on at all times, unless a lockout is applied at the main panel.
The other option I'm considering is to have air/power on if either the fence is closed/locked OR the teach pendant is enabled.
Thoughts?