Question about "safe" speed of moving machine part

ndzied1 · Jan 30, 2019

I have a colleague who has said that OSHA considers motion slower than 10in/sec safe and that you don't have to guard it.

I have never seen this figure cited anywhere and think you have to take every situation as unique and give it a risk assessment. And for OSHA purposes at a minimum you have to start with guarding requirements for all machinery and then apply machine specific standards.

Has anyone ever heard of this 10"/sec reference and if so, could you provide a standard number or reference to it?

Thanks

Aabeck · Jan 30, 2019

I have never heard of that.

But, 10 inches in one second is quite fast to me. I work on a few conveyor line processing systems and moving product at 10" per second would be fast. They generally run from 2 to 10 feet per minute - about 1/2 to 2"/second.

Maybe they found a spec that was 1.0"/second somewhere and speed-read over the decimal point?

Dravik · Jan 30, 2019

Probably reading a portion of an old guidance

Code:

OSHA Instruction PUB 8-1.3 SEP 21, 1987 Office of Science and Technology Assessment

Most robots are set up for an operation by the teach-and-repeat technique. In this technique, a trained operator (programmer) typically uses a portable control device (commonly referred to as a teach pendant) to manually key a robot and its tasks. Program steps are of the up-down, left-right, in-out, and clockwise-counterclockwise variety. Robot speeds during these programming sessions are required to be slow. The ANSI Standard currently recommends that this slow speed should not exceed 10 in/sec (250 mm/sec).

Part of their guidelines for robotic safety and to the best of my knowledge ONLY applied during programming sessions and wasn't applicable to normal operation.

Pretty sure there's better guidelines on safe speeds elsewhere.

Aabeck · Jan 30, 2019

I still think teaching a robot at 10"/second would hurt when someone got hit, and the robot wouldn't even know.

Hold 2 fingers 10" apart and try to move one to the other in 1 second. That looks like it could do some damage if it were metal and driven.

jimtech67 · Jan 30, 2019

What about getting pinched between the moving part and immovable object like the machine frame etc....

Steve Bailey · Jan 30, 2019

It's quite a long leap from that 1987 OSHA instruction that says speeds during teach mode should be limited to 10 IPS to a generalization that speeds under 10 IPS don't need guarding.

shilok · Jan 30, 2019

I've head of it from few expert that helped us with risk assessment.
10 in/s or 250mm/s comes from attached Risk Estimation & Evaluation Table AFAIK.

bill4807 · Jan 30, 2019

Never heard of it in normal operation.

Timbert · Jan 30, 2019

The 10 inch/s or 250 mm/s comes from RIA R15.06-1999.

It does not say that if a robot moves at that speed or slower than it does not need guarding. What it does say is that if the speed is limited to less than 250 mm/s then when doing the hazard analysis that you could consider that avoidance was 'likely.'

In fact, according to the RIA spec, the only way to avoid a barrier requirement is to move that slowly and have only 'infrequent exposure' to the hazard and that the severity of injury only be 'slight.'

James Mcquade · Jan 30, 2019

if its moving and you can touch any part of the machine or part being processed, it must be guarded.
if the opening is bigger than 15mm (best as I can remember) the opening must be guarded.
if it's a robot, it must have a fence and lockable safety door connected to the safety circuit - again this is from memory.

that was what we had and still have to design by.

james

Aabeck · Jan 31, 2019

In regards to the OP it brings to mind: A little knowledge is a dangerous thing.

Some CEO or plant manager heard somewhere, years ago, about this guidance, remembers it out of context, and wants things changed to increase production, decrease labor or machine costs, etc.

Similar to the one I was asked about regarding the staggered startup of motors, one per 5 seconds. Someone remembered it as one per 5 minutes and wanted all his motors and HVAC units on 5 minute startups. I told him if it were 5 minutes that some motors would take an hour or longer to start, or may potentially never start.

Question about "safe" speed of moving machine part

ndzied1

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