kolyur
Lifetime Supporting Member + Moderator
I'd like to hear some opinions on how to handle safety of pneumatic actuators on machinery. Traditionally, most of our equipment would be surrounded by hard guarding. When a guard door is opened, the main dump valve would release--no safety issue. However, with some newer equipment we are using light curtains and don't necessarily want the air to dump every time the curtain is broken. Ideally I'd like the machine cycle to pause until the curtain is reset, then continue. We also use servo actuators and robots, but these have hardwired safety such that they are mechanically locked out and will immediately stop whenever the curtain is tripped.
The pneumatic devices are trickier, however, because at any point in the cycle, some of them will be actuated and power needs to remain on those valves to keep them in position (we typically used single solenoid spring return valves). So I can't just dump the air or drop power to the output card. What I've been doing is writing my PLC logic in such a way that the valves cannot shift if the curtain is tripped. This works but makes me a little nervous because I'm handling a safety function through a non-safety programmable device.
Is the solution to use double solenoid valves, so that the valve signal can be dropped without shifting the valve? What part should a risk assessment play in this decision? We do light assembly and most of our pneumatic actuators are small enough that they couldn't cause more than a swollen finger.
Thanks for your suggestions.
The pneumatic devices are trickier, however, because at any point in the cycle, some of them will be actuated and power needs to remain on those valves to keep them in position (we typically used single solenoid spring return valves). So I can't just dump the air or drop power to the output card. What I've been doing is writing my PLC logic in such a way that the valves cannot shift if the curtain is tripped. This works but makes me a little nervous because I'm handling a safety function through a non-safety programmable device.
Is the solution to use double solenoid valves, so that the valve signal can be dropped without shifting the valve? What part should a risk assessment play in this decision? We do light assembly and most of our pneumatic actuators are small enough that they couldn't cause more than a swollen finger.
Thanks for your suggestions.