GuardMaster PLC question and......

[ceilingwalker]

Hello all. I am purchasing a CompactLogix to use as a server which will host 4 other PLC's (2 ControLogix, 2 Beckhoff) and a Fanuc RC. The current system has safety mats with individual Sick Safety Modules. This server PLC is going to be controlling the robot using inputs from each of the PLC's in this network. Finally at my question, when does one need to use a Safety PLC as opposed to a non-safety rated PLC? I am thinking because all I am doing is adding a robot to this system, and the system already has machines with machine safety in place, a standard (if that's the correct word) PLC should be fine, right? Also, I don't really need any I/O points for this PLC since it will all be E-net IP. I think I would like some embedded discrete I/O just for gits and shiggles. I know I need a hot rod processor with horsepower but not a lot of memory. I am hoping someone who has integrated a robot with existing PLC's might be able to recommend controller for me. Thanks in advance.

 

[mk42]

Finally at my question, when does one need to use a Safety PLC as opposed to a non-safety rated PLC?

You need a safety PLC when you want the PLC to be part of a safety system.



99% of safety questions come back with this answer: What does your risk assessment say you need?
The process currently has safety in place (which is a good start, assuming it's correct). How will adding the robot affect the existing safety? Are there new hazards? How will the robot's safety be managed?

In my area, we typically have safety PLCs to communicate standard and safety data over ethernet (profinet in my case, but could be EIP or whatever) to the robot. However, most robots have IO that can be used for safety, and depending what you're doing, it could be that you just need to link them to the existing safety relays, or add another safety relay for the robot.


Note also that (especially in the US) if you touch it you own it. If you don't feel comfortable doing the safety assessment on your own, there are definitely companies out there that will do it as a service, but you need to consider the system as a whole, and not just the robot, even if the robot is the only change you're making.

 

[ceilingwalker]

You need a safety PLC when you want the PLC to be part of a safety system.



99% of safety questions come back with this answer: What does your risk assessment say you need?
The process currently has safety in place (which is a good start, assuming it's correct). How will adding the robot affect the existing safety? Are there new hazards? How will the robot's safety be managed?

In my area, we typically have safety PLCs to communicate standard and safety data over ethernet (profinet in my case, but could be EIP or whatever) to the robot. However, most robots have IO that can be used for safety, and depending what you're doing, it could be that you just need to link them to the existing safety relays, or add another safety relay for the robot.


Note also that (especially in the US) if you touch it you own it. If you don't feel comfortable doing the safety assessment on your own, there are definitely companies out there that will do it as a service, but you need to consider the system as a whole, and not just the robot, even if the robot is the only change you're making.

All of my experience has been integrating FANUC CNC machinery with other PLC's and I don't expect this to be a whole lot different. This is a FANUC robot and I have the DCS options and the SR's that come with the robot. Since this is a system that already has an iron clad safety system for each machine in place, I intend to just have those report back to my server PLC that all is well or not. What I have used in the past (for CNC machinery) was determined by how many access points or areas where a human can enter a machine and get hurt. If it exceeds the number that a simple safety relay can manage, then I go to a safety PLC. Also, if logic is required to allow entry to an area whilst the machine is running, but at safe speed.

 

[bill4807]

I second completely what MK42 said.
And if i am reading it correctly you are adding a robot that will communicate with other machines/processes. That plc for non-safe IO you can use a standard plc.
But in my experience if i add a robot to tend existing standalone machines you will come across circumstances where the stand alone machine safety circuit will not protect.

Therefor needing to add more safety rate components to the new portion of your system that ties all the machines and robot cell together.
For instance a CNC machine on its own may have door interlocks for its intended purposes. BUT what happens when that CNC machine has 2 operator doors and one of them falls into the robot guarding (being protected but the cell interlock) but the other falls outside the cell guarded area..
Which creates a hazard because now if the cnc door that falls outside the guarded area is opened the cnc will not operate as it should but someone is now reaching into the CNC machine through that door and the robot tries to load/unload..because you werent monitoring that CNC safety door switch with the robot safety circuit or DCS.
Just one example.
So in short you may need more safety IO after you evaluate the entire system now as a whole, instead of 3 machines and a robot.

 

[JeffKiper]

I hate safety relays!!!!! OK now that that is put of the way.

Just like MK42 said . What does the risk assessment say? Once you touch the system you own it. It spund like you are modifying an existing system not just monitoring. You modify the system you get to re-evaluate the system requirementsand re-validate the system.
Remember they employee can go after you civilly in the US. If you ha e all your ducks in a row it makes it extremely difficult for them.
L

 

[ceilingwalker]

But in my experience if i add a robot to tend existing standalone machines you will come across circumstances where the stand alone machine safety circuit will not protect.

I understand what you're saying. I was thinking the Fanuc DCS and on-board SR's could handle its portion of the cell, then the individual machine safeties already in place could handle theirs and go in series back to the robot. Any breach in safety will result in zero robot movement and an e-stop condition.