Robot Cell Safety Door Circuit

Jieve

Member
Join Date
Feb 2012
Location
USA
Posts
274
Hello,



We have a Stäubli RX130 robot arm in an enclosed cell with a safety door to be used for educational purposes and we are in the process of setting up the safety circuits. The door is equipped with an AZM 160-14yrpka solenoid lock mechanism, which has 3-sets of positive action NC contacts (closed while the door is closed) and a solenoid lock which operates a set of NO/NC contacts. The NO contacts are closed if the door is closed AND locked, and the NC is closed if the lock solenoid is not engaged. The schematic diagram of the lock is attached.
We are planning on wiring this solenoid dual channel to a safety relay to cut power to the robot when the door is opened.
However, I have a question about best practice use of the door lock solenoid and the NO/NC contacts. We were planning on having the lock solenoid be controlled by the E-Stop circuit, in other words the door is locked when power is applied and no E-Stop has been activated. The NC contact on the solenoid would be wired into the reset circuit on the E-Stop circuit, so the solenoid must be inactive for the system to reset. However I still have a leftover set of terminals (1,2 in the diagram), the NO which is closed when the solenoid is active AND the door is closed.



Initially I was thinking of possibly wiring these to activate a separate contactor, whose contacts would prevent powering the robot in case the door lock solenoid lost power, even if the door doesn’t open. But this seems like it would add extra complexity and I’m not sure if it would be a standard solution.
So my questions: Does this safety setup and solenoid lock control method sound ok? And what exactly would you use the solenoid NC/NO contacts for?



Thanks!

Door Lock Solenoid Schematic.jpg
 
If you open the door, the 3-sets of positive action NC contacts open and the
Robot will stop.
If you don´t want anyone to open the door while the robot is working, you will NOT energize the lock solenoid. You only energize the solenoid if the robot is not moving. you can use the solenoid aux. contacts to tell the operator that he can open the door, turn on a light etc. If you have an emergency, then you use the emergency switch and the safety relay.

You only need to use the door safety switch with the solenoid, if you don´t want no one to open the door while the robot is running.
 
First thing you should do is a risk assessment. The outcome will determine as to what standard of safety should be engineered and applied.

At a minimum you need to monitor your robot, pneumatics, hydraulics and power. Once it is in a safe state the lock can be unlatched by means of a push button.

I have installed a similar system, engineered by others. The main concern was crush due to hydraulics still moving. Hydraulic pressure and cylinder movement were monitored and the electricals safety isolated. Electrical isolated items included 24 gang saws powered by four 220 kw electric motors, so in short safety was paramount
 
Thanks for the responses.

@Nonuke: I'm not understanding this, you're saying keep the door unlocked as long as the robot is moving? Turning on the solenoid locks the door. Also, was thinking that the aux solenoid contacts should/would be used for some part/function in the safety circuit.

@Borabee: main thing is we want the robot cell to remain inaccessible as long as the robot and any accessories (pneumatic in our case) are powered ... currently there are no accessories yet as this project will be added to over time. But for now I'm just trying to setup the safety door curcuit and am looking for input as to the safest/best way to use the lock switch we have. This setup was originally used at a local plant and was donated to us, but we don't have complete wiring diagrams of the original setup. Any tips on how you would use this lock setup in a safety circuit or how a few details on how the safety controls were done in your system?

As far as i can tell from the robot controller manual, all disengage inputs are treated as e-stops internally. It's just a matter of us deciding how to setup our external estop circuits to activate/deactivate these signals to the controller.
 
Thanks for the responses.

@Nonuke: I'm not understanding this, you're saying keep the door unlocked as long as the robot is moving? Turning on the solenoid locks the door. Also, was thinking that the aux solenoid contacts should/would be used for some part/function in the safety circuit.

What I said is that the operator will NOT be able to open the door if the robot is moving. In this situation, the solenoid should be locking the door. When the robot isn't moving, the solenoid should unlock the door and the operator can open it if he wants to. If the door is open, the robot should not start. Aux. contacts are not safety contacts. They are just contacts used to give information.
 

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