Impact deceleration for robotics safety

[adamshir]

Hi,

I'm working on figuring out how badly a person gets hurt if hit by the robot. I was planning to determining this using F=ma. Given a force I was hoping to find someway of correlating this with severity of injury to give me a rough idea. I've worked out the top speed of the robot, the weight of robot+payload. The only thing I'm missing is a decelleration value to determine the Force. I tried assuming a decelleration time time of 0.1sec but I'm not sure if this this realistic or not.

Does anyone have any ideas or suggestions about this.

Thanks

 

[MintJulep]

F = ma is probably too simplistic. I think you need to consider energy in the mix. The magnitude of the force in comparison to a person is important too.

 

[GregLocock]

0.1 seconds would be a fairly slow decel.

I think you need to describe what is going on a bit more fully, is this a collision between a pedestrian and a mobile unit? or a blow from an arm?


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[adamshir]

Hi

Thanks for the input thus far.

I'm looking at the safety guarding aspects of a laboratory automation application for a biotech company. The robots are Scara type robot arms with Z-axis capability and are table mounted.

What I am trying to do is get a feel for the injury that being smacked by a robot at max speed with max payload will have on a person. This will provide the appropriate argument for me to show the value added to the barriers/light curtains. I was reading through the R15.06 ANSI standard which is referenced by OSHA, they have a section on choosing the appropriate guarding relating to injury. I know I can put up these big barriers but what my customers are looking for is a safe way to access the unused instruments while the system is in operation by having the instruments on slides or turntables.

The robots used in this application are not the heafty industrial robots used automation type plants they are a bit smaller. It would be nice to have some rough calculations to show that being hit by the robot at max speed and weight would cause permanent damage (the robot seems too puny to cause death).

How is this handled in other industries ? do you automatically assume being hit by a robot causes irreverable injury to a person ? If not how does one go about correlating the impact of a robot with severity of injury ?

Thanks again for the feedback

Cheers

 

[MintJulep]

Have you tried contacting the manufacturer of the robots, or manufacturers of light barrier systems?

You can't be the first one ever to try to do this. Perhaps they could offer you some direction.

 

[caravoy]

In practice, you just don't want to get hit by the robot. Design so that at max reach with largest payload, there is no way to hit the operator. You can use turntables, slides, etc. If space does not allow, go with safety interlocks using axis limit switches, light curtains, etc. Showing somebody your calculations after they've been hit with the robot, even if it does no major damage, won't go over too well. Good luck.

 

[tygerdawg]

DITTO THAT on caravoy

Never design a robot system that allows human access to the workspace while power is on the servos and the machine is in auto operation. ANSI/RIA 15.06 covered this, and that's all the justification you need. Access is permitted only on teach mode, which requires reduced voltage to servos and reduced speed. Guard it, and control access through Schmersal gate switches or similar. I don't like light curtains because folks tend to stick their elbows through them and cause and inadvertent e-stops.

It doesn't matter what the impact force is. Which, BTW, is probably too difficult to try to calculate (KE = 0.5mV^2, coeff of restitution on a human body, area of impact, yadda yadda yadda) and should be done experimentally.

Anything less on an OEM product to a customer is a recipe for a liability lawsuit.

TygerDawg

 

[BillPSU]

Allowing operators near a robot no matter how fast and whatever load can be a problem. Someone gets real close and has an eye damaged. How much load and speed does it take to damage an eye?

Guard the robots safety like this should not be compromised.

 

[GregLocock]

In our industry the designer of the enclosure would probably be sacked if the robot ever hit an operator. If the operator disabled the interlocks and then got hit he would be sacked. If the maintenance guys overrode the overrides and got killed then they wouldn't be sacked. if they weren't killed by the robot then they'd be killed by plant safety.

Does that put it in perspective?





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.