zlacker

>>ummonk+(OP)
Servo based systems are both incredibly power and incredibly fast. So fast that if you've never seen a servo based arm move at top speed and come to that top speed at top acceleration you'd be forgiven to think that I'm exaggerating.

Depending on the application there are different layers of safety surrounding these systems, including perimeter guards, optical barriers, limit switches, resistance based detection and so on. But when a system is broken someone has to go in and fix it, and you tend to do that with the robot powered up, some of the safety systems disabled so you can actually work on it and if you're really unlucky a motor will end up shorted against a + or - rail while you're within reach. This is obviously dangerous, and it is more dangerous because broken equipment can't be trusted to behave in a predictable way.

They won't stop. Not until whatever is obstructing has moved or the motor has burned out (or someone has the presence of mind to hit the e-stop). I've seen a 3" thick mount that must have weighed well over a ton sheared clear of its bolts (which themselves were an inch thick) by a malfunctioning servo on a very large lathe under construction (think 8 foot chuck for crane cable idler wheels). Do not fuck with servo systems unless you are 100% sure they are safe to approach or you may well end up dead or gravely injured.

>>jacque+65
> and you tend to do that with the robot powered up

I thought OSHA and friends didn't allow this. Lockout/tagout is standard.

> some of the safety systems disabled

There's a simple one which ought to be more common: current limiter on the drive power supply. Makes everything slow and weak.

>>crotch+m8
> I thought OSHA and friends didn't allow this. Lockout/tagout is standard.

Yes it is, for plant workers it is a firing offense in many places.

But your typical maintenance tech that is supposed to work on the machinery itself rather than just to be using it may well use lockout/tagout to ensure that the machine is powered off when they are working on it and don't need to be able to do any kind of diagnostics. But short of a complete disassembly and testing each component in isolation - for which there often isn't really time and which given the pressure on maintenance technicians to get a piece of gear working again - people tend to take shortcuts such as to hook up analytics gear to a machine that is live. Stupid? Yes, absolutely. But this kind of stupidity is the result of usually many years of things working just fine and bad practices creep in. The guy that manages to get stuff done rapidly is the one that gets called out. And eventually an accident will happen. Weirdly enough even near accidents tend to reinforce the belief that it worked. When actually the lesson should be that it didn't but the person just got lucky.

One very memorable occasion at an industrial plant I visited is that someone got beaten up for removing a lock and I felt absolutely no sympathy for that guy. He could have well gotten someone killed (large 5 axis mill).

>>jacque+cr
Yeah, that tracks. Workers in plants like that don't have a lot of patience for someone trying to get them killed. People always accuse manufacturing and construction unions of "using safety as a cudgel", but the reality is that a lot of these people have lost friends to industrial accidents and they're elected by workers who care a LOT about safety. Sure, they're political and they are going to bargain and pressure in labour disputes, but they are also genuinely fanatical about safety. Some of the most ugly union/management interactions I've ever seen was union safety reps who had personally seen their comrades die in industrial accidents arguing with management who had a bad safety track record and very much gave off the vibe of neither caring nor understanding as to why you couldn't lift four-point hoisted concrete slabs within horizontal metres of workers at ground level, no matter how tight the construction space is. The reason, if anyone is curious, is that suspended heavy slabs where one or straps break won't fall straight down, they swing away from the side of the straps that broke and then swing back, and the remaining straps past their safety limit can break or lose hold at any time. You don't have to be underneath a multi-point load to be able to be crushed by an accident, you just have to be in the general vicinity, so to do it safely you have to evacuate said general vicinity and have an on-site safety officers who understands the physics of the thing to make sure people are standing far enough away.

>>lucubr+IH
I've almost f'd up myself using a portal crane indoors. I lifted a relatively light rotor of a windmill onto the stator only to find out that the magnetic field of the rotor was strong enough to lift the entire assembly, including a 500 pound welding table clear off the ground when it came close enough. Seconds prior my fingers were in the airgap between them (still quite large). I had to take a long break after that before going back in, the surprise factor really got me, I absolutely never saw that one coming and a very large part of working safely is to be able to predict the failure modes. I hadn't counted on 'anti-gravity'.

Roughly halfway into your sentence about the concrete slab my mental kinetics prediction model already declared a zone described by the pendulum at maximum extension (hanging from one remaining strap) as no-go area. And depending on the state of the crane and how far debris could have been shot out from a falling slab that area may well have had to be much larger still. People that don't understand such dangers should not be in management positions, which is one of the reason why I'm always happy to see industrial companies that promote people from the ranks to management rather than to bring in outsiders with only theoretical knowledge.