My neighbor's kid asked me why elevator doors have those little rubber fingers

I was working on a door operator in a Seattle office building last week, and this kid from the law firm next door was watching. He pointed at the safety edge and said, 'Are those so it doesn't pinch people?' I mean, yeah, obviously, but then he asked, 'Why do they look like that, and not just a flat bar?' I had to stop and really think about it. I explained how the individual rubber fingers can bend around small objects or an arm, breaking the light beam and telling the door to open back up. A solid bar might not catch something thin. It made me realize I just take that design for granted after seeing it a thousand times. I never really thought about why it's specifically shaped that way. Has anyone else had a simple question make you rethink a basic part of the job?

2 comments

2 Comments

ryanh917d agoMost Upvoted

That's a really good point about the dog leash, @the_alice. It makes you see how a solid bar would just slide right over something thin like that. The rubber fingers are basically a mechanical backup for the light beam, feeling for stuff the light might not break. It's a clever way to make the door sensitive to both big and small things. I guess the design had to solve for a kid's arm and a purse strap at the same time.

the_alice7d ago

That part about the rubber fingers bending around small objects is spot on. I've seen them catch a dog leash that a flat bar would have missed. It's one of those designs that seems weird until you see it work.