Hello, Im looking to connect a CLICK PLC to my robot, so I can control solenoids and other tasks. How would I go about connecting IO? Im fairly new to this so thank you.
It’s fairly simple, if you’re just exchanging digital signals. 
It’s also possible to set up MODBUS for exchanging of many signals and data, but that’s more comprehensive.
Connect a digital output from your robot to a digital input on your PLC, if you want the robot to signal the PLC.
Connect a digital output from your PLC to a digital input on your robot, if you want the PLC to signal the robot.
In both cases you will have to connect a 0V/GND of the robot to a 0V/GND of the PLC (for example the 24V power supply). This is already done if you power the PLC through the robot terminals.
Am I able to power the plc through the controller? Would you know of any good documentation or processes for that? Honestly this has been the most confusing part is that my other devices are powered by an external 24v psu. Im currently using relays and was worried I would need a relay for every input and output. How difficult would setting up a Modbus be? Does it allow me to just negate any wiring of inputs and outputs to the controller and just have everything to the plc? Lastly is it dangerous to share grounds of two different 24v power sources?
Thanks a ton.
Check the current draw on the PLC’s documentation. The UR’s internal power supply can provide 2A total on the IOs. You say your other devices are powered by an external power supply. Might be worth realizing you can power the UR controller on the same external power supply. Just remove the jumper wires on the power terminal and wire in your external supply. See article here: Universal Robots - Good practices on powering energy to your cobot
Modbus is pretty straight forward. You just configure it with the teach pendent and yes CAN completely remove physical wiring. Usually the more difficult side is the PLC implementation of the MODBUS protocol.
It could be “dangerous” to share grounds on 2 different power sources, but really the problem here is that if you’re mixing and matching grounds, you aren’t going to get ACTUAL 24v. You might get some weird floating voltage like 18v. You are only guranteed the rated voltage from the SAME SUPPLY’s circuit. You can’t trust taking 24v from one supply and grounding it with a different supply. This is why the controller is designed to be powered by an external supply. That way everything shares the same ground.
This helps a lot thank you.
What’s the theory behind your last part? I have never heard of that issue, and I have grounded many 24V supplies together without issue.
The issue with floating voltages between supplies happen, if you do not ground the two 0V together, doesn’t it?
The dangerous part should only happen if you connect the 24V of two supplies together.
I always prefer to use the built-in 24V of the UR for its own circuits and then having an external 24V supply for a PLC and that circuit, since I then know that the 24V turns off and on with the UR and in case of faults in the robot. Without the need of a safety circuit for achieving this.
You’re right. I was a little jumbled. I honestly am not sure what I was thinking there lol. You’re definitely right.
I’m glad I hadn’t been doing something wrong up until now.
So does that mean im able to share the “0V” of the outputs? Needing to now route outputs to an external box, I have a perfect 9 pin cable but if I cant share "0V’ then im going to need at least a 10 pin cable. (5 solenoids). If so where would it be smartest to take it from?
You can share the 0V between two supplies. However, you want to control 5 solenoids, which all need 24V and 0V to turn on/off. That’s something else entirely than what has been discussed up until now.
The only thing you must confirm is the current drawn by the solenoids and the gauge of your cable in that case. So I am confident you’re alright.
Any of the 0v terminals on the UR are the same. We usually pull a line from the 24 and 0 of the conveyer tracking terminal block, since we never actually use that. It offers a little bit of visual distinction for us so we know at a glance that those wires are not inputs or outputs
Yea, sorry i piggy backed of this thread to ask that question. Im assuming each solenoid takes 200ma. I don’t have a DC amp meter unfortunately. Thank you for the help.