Pneumatic Safety Standards

Hello,

According to ANSI B11 and any other applicable standards in the US, is there a written standard on collaborative safe force of an air cylinder or electric motor? Can we design stuff so that people can work around these components and not need to turn it off completely?

I can't seem to find anything that tells me, but surely there's a threshold for this. I guess the flip side of that is a force acting on sharp object would cause more harm than the same force on a larger flat plate.


Thanks!

I'd expect, anything using high voltage will have to much capability and force to not need lockout to be safe to directly work on either power or mechanical.

I think if one reads up on LOTO, ALL energy must be reduced to zero, all STORED energy must be either dissipated or kept from being energized. The process/machine must be locked out and tagged or if incapable of being locked out then a tag must be used. An attempt must be made to start the machine/process after it is locked out and it must not start or energize.

Even a small air jet that just blows a small defective part off of a belt can do serious damage to say an eye, safety glasses not withstanding.

I don't work with pneumatics as much, so I can't answer that half. I'm also not as familiar with the specific US standards.

However, I've used a number of drives (usually servo drives) that have safety built into the drive itself. There are a number of safety functions. Safe Torque Off (STO) is the basic "take all electricity away from the motor", but there are others. Safe Limited Speed (SLS) allows the drive to operate within an allowed speed range, but shuts it down if it detects a deviation. I've also seen safe positioning modes, where it ensures the drive only moves a certain direction or within a certain allowable range.

See manufacturer link below as an example. They are usually used together with a failsafe PLC, but can be with a relay or standalone.

https://www.industry.siemens.com/to...ages/safety-drives.aspx?tabcardname=functions

The goal is always to do the safe thing, but sometimes it can be safer to keep the energy in the system. As an example, a motor lifting something stores energy in the lifted object. If you simply cut power without braking first or otherwise supporting the load, it would come crashing to the ground.

For a LOTO situation, I'd definitely expect the 480V to be removed from the drive in the first place. However, I've definitely seen cells with a "maintenance bypass" mode where the drives are allowed to jog very slowly, or move only within half their usual travel.

This is similar to the concept of a robot in teach pendant mode, where the robot programmer needs to be up close and personal with the robot to make sure the points are correct.

What type of application are you building? There may be limits specified in type C standards. For general applications, take a look at ISO TS 15066. You can find limits for various body parts in table A.2.

LOTO says that ALL stored energy must be released to work on equipment.
My 2 cents is this, and if I am wrong, please correct me.

Each system is different!
you must look at the entire system and see what is going on.
you must then do a risk assessment for each cylinder for a loss of air pressure and the restoration and initial powering of the valve to see what the potential hazard is.

for example, dumping the air pressure on a cylinder that had pressure on the retracting side of the cylinder is dangerous. when you energize the cylinder the first time, the cylinder will extend like a rocket until it hits something or goes to the end of travel. even when it hits something or at the end of travel there is the potential to destroy the cylinder or break something, parts can fly.

I hope this helps,
james