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.
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.
I got hit right in the dick by a milling machine axis lever spinning up full throttle.
Only once, never again. Still surprised something terrible didn’t happen - hurt like a bitch. Shop dude says it happens pretty often though because people don’t look down at the caution tape telling you not to stand there.
All of that is to say that it seems like working on a manufacturing floor with robots has the potential to be so so dangerous. Getting into a rhythm and doing repetitive work all day, it’s easy to imagine slipping and ending up as human soup.
This is 2023 and we are well into the age of ubiquitous, cheap, small cameras.
Place cameras such that paths can be observed at a safe distance and diagnose problems in powered machinery without placing a person in harm’s way.
My own process to ensure things were safe was to first run it in air without the spindle powered up, then on foam, chalk, and finally on aluminum in that order before progressing to steel.
And that saved my ass more than once.
What does work is to disconnect the motors while keeping the rest of the electronics powered up but not all industrial robots have such a facility. The e-stop will disconnect everything and that stops you from doing things like firmware upgrades. And when things are broken it gets even more complicated and unpredictable.
Servicing machinery like this is difficult, sometimes dangerous (but not even the most dangerous, for that you have to go visit a steel mill) but not impossible. The biggest danger really is familiarity with the machines to the point that you stop to respect them, that's when you are really in danger. Personally you can't pay me to go near one when it isn't locked out, I'd much rather field strip it and test the components one by one than taking a risk but a service tech might be promised a bonus if they can get it working again quickly and that might cause them to work in less safe ways.
I've seen people do incredibly stupid stuff with machinery and I've also seen the results in terms of fingers and sometimes eyes or whole limbs lost as evidence of prior fuck-ups. And some of those people still took risks afterwards.
Walk into any metal machining shop and just watch, it won't be an hour before you see someone do something that they shouldn't be doing. And in almost all cases it will end up without anything being damaged or someone being injured. One more step on the 'normalization of deviation' track. It always ends the same.
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).
Now experts will also do stupid shit, but they are the ones who should be able to judge what risks are involved.
https://www.bloomberg.com/news/features/2017-03-23/inside-al...
And before anybody sees that 'Asia' comment as somehow politically incorrect: the statistics are pretty damning, Asian operators abroad have less than stellar safety records and very high pressure on industrial workers to meet their (sometimes unrealistically high) quotas and I would not expect them to do any better in their home countries.
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.
Then we should work towards fixing broken robots using working robots.
The machine plunged into a large block of aluminum at full rapid speed with a 1 inch rougher end-mill. It then proceeded to run the cutting program, again, at full rapid rate. The sound it made is something that I will never forget. This thing was churning aluminum like it was butter. It was literally turning it into goo, not cutting it at all. It did not care one bit. The cutter was large enough and stubby enough that it did not break.
These things are fast enough that, by the time your shocked brain is able to respond it could have killed and dismembered you five times before you can even think of slamming the e-stop button.
The end-mill came out with a ball of aluminum, 2 inches in diameter, permanently welded to it. It was one of the scariest industrial accidents I've been around. Thankfully the enclosure and rigidity of the machine made it so that the only consequence was aluminum that looked like churned butter.
Years later I worked with an aerospace client who uses stir welding to assemble rockets. Same process, except you are doing it on purpose and with controls. The idea is that stir welding preserves the metallurgical properties of the material, whereas TIG/MIG welding might not preserve properties important to the design.
To echo your other comment, since that happened I learned to never trust CAM software or simulations, always run it on air first and, if necessary, machinable wax blocks. Decades later, I still don't consider myself a machinist at all. I am pretty decent at it. It's a complex art that requires time and dedication. I do too many other things to be that guy. I do have a VF-2 and a Bridgeport knee mill (full manual still) in my garage though...
I have a 30 Watt diode laser that came without any safety measures at all. It kind of surprised me that you could just fire it with a G-code and absolutely nothing stood between you and the beam. It cuts wood like butter though, up to 20 mm in a single pass (solid wood, not birch ply) and I'm super happy with it but that tool is going to go through some serious modifications to make it safe. It can set just about anything on fire fair distance away and will fry your eyeballs from half a kilometer if not more. Any idiot with a few bucks to spare can go and order one and they have absolutely no clue about the kind of damage a machine like that can do. It looks so innocent, it's completely deceptive.