By Professor MC, Motion Control Guru, PD&D
Hello again my faithful motion control minions and pinions.
I come to you today with a lengthy response that resulted from a young gentleman’s perplexing question.
At a recent industrial automation conference, I wheeled myself over to a crowded booth where the man looked at me, pointed to a red mushroom and asked, “So, how much longer until these [emergency stop switches] are obsolete?”
I was shocked. Of course, the continuous advancements in emergency stop switch (ESS) design, construction and interfacing will experience ongoing improvement. But also, the understanding of how and when to use an ESS, as well as what type of device to use, will continue to greatly improve — and certainly not become obsolete.
Now, an emergency stop switch is not considered a safeguarding device even though it fulfills a safety function classified as a complementary protective measure. The devices that fall into this classification augment or ensure the proper operation of safeguarding and are designed to enhance the safe use of the machine.
So said ANSI B11.19, “A safeguarding device detects or prevents inadvertent access to a hazard, typically without overt action by the individual or others. Since an individual must manually actuate an emergency stop device to issue the stop command, usually in reaction to an event or hazardous situation, it neither detects nor prevents exposure to a hazard.”
Or, “Don’t use an ESS instead of proper hazard safeguarding.”
ESS enhancements have greatly improved over the years, including common sense changes that shouldn’t have taken so long.
Believe it or not, but the unified color scheme, red button, yellow background, was a big deal in making sure “individuals readily understand what will happen if they hit that button.” Here are some other improvements:
- Positive opening designs have ensured that contacts open when the switch is actuated.
- Re-arming the switch must now be a deliberate action, such as twisting or pulling the button.
- Technologies such as fiber optics and pneumatics can be used to signal the machine control.
- Improved testing procedures have reduced the possibility of a catastrophic failure.
My response to the engineer-in-training wasn’t as long and it still tested his patience — kids these days.
I did add that I expect better incorporation, harmonization and explanation in the future. This includes all emergency stop devices within ANSI B11.19 “Performance Criteria for Safeguarding” and ANSI NFPA79 “Electrical Standard for Industrial Machinery.”
Until next time, I’m headed back to my cube …