Can High Sensitivity Be A Disadvantage?
Interestingly, while high sensitivity is often touted as a benefit, it can sometimes compromise safety. As this claim is not completely intuitive, I would like to spend a little bit of time elaborating.
Imagine two different robots which in all regards are identical (same payload, reach, PFHd values etc.), except for the sensitivity of the force limiting safety functions. Where one robot has a sensitivity of 1N and the other has a sensitivity of 50N. The question is which one is safer in a real world application?
If we consider the values in ISO/TS 15066 we can see that both robots are sufficiently sensitive to stay within the guidelines (please bear with me that I’m grossly oversimplifying things here, but the point remains valid). And if we assume that the PFHd values for both robots are below the 10-6 failures/hour threshold the immediate conclusion is that both robots are sufficiently safe.
However, the ultra-sensitive robot may face an issue of 'nuisance stops' caused by minor disturbances like a loose cable or an accidental touch. Nuisance stops in itself isn’t really a safety problem, the problem is how it affects the behavior of the people around the robot. Nuisance stops are really annoying for the user of the robot (for good reason, they kill productivity), so they can be a sufficient source of motivation for someone to try to bypass or disable the safety function altogether.
Generally speaking, a well-designed safety function should strike a balance - it should be sensitive enough to ensure safety but not so sensitive that it encourages workers to circumvent it. The very best safety functions are the ones which keep you safe, without you ever noticing.
So next time you come across a video showcasing a robot's safety function, remember, there’s more to the story. Safety requires thoughtful consideration and understanding. It's not about the robot stopping at the mere touch of a balloon; it's about ensuring that the robot consistently and reliably performs safely in its operational environment.