Advances in wireless technology bring hardwired emergency-stop systems to a new level of safety to speed up response time, free operator constraints and expand applications.
By Marty Weil, Contributing Writer
Emergency-stop, or “e-stop,” pushbuttons are a familiar — and critical — component for automation systems; they stop motion to help prevent injury to workers or damage to machinery. In an emergency that might escalate into a hazardous situation, an operator presses an e-stop button to halt the machine, preventing further risk to the worker or the system.
While industrial firms have installed these devices for decades as the intercession point of emergency stop systems, the advent of wireless control technology for e-stop buttons is beginning to change this process in a host of applications.
Augmenting Hardwired Solutions
Traditional, hard-wired e-stop devices have prevented countless accidents, but sometimes are not located within easy reach or in the safest possible location, impeding situations where speed is vital.
“Someone has to either carry a pendant with a robust and rugged cable that's very heavy — which hinders their mobility — or they have to move from their position to a station with an e-stop switch and hit the button, which takes valuable time and might not be possible under the emergency situation that has arisen,” notes David Stagg, product manager for industrial remote control products, at Warren, Ohio-based Laird, a participating Encompass™ Product Partner in the Rockwell Automation® PartnerNetwork™.
This is where a wireless emergency stop switch comes into play. In recent years, advances in technology have changed concerns about whether wireless emergency stop switches can be achieved safely. “Today, we're able to offer wireless e-stop switches that are reliable and safe,” says Stagg. This development is changing the game in e-stop systems.
Control on a Single Channel
According to Stagg, a key change involves the secure RF transmissions between the stop controller and the machine control device. While the rest of the control safety system is fully redundant, the link from the wireless safety stop to the machine control is on a single channel. Laird engineers needed to find a way to make that single-channel communication (via an RF telegram) totally secure.
“If the RF telegram is lost or corrupted in any way, the stop is initiated,” explains Stagg. “Every single frame of data that is sent out has a time-related section to it that protects the packet from anyone capturing the message and manipulating or rebroadcasting it.”
The bottom line: It protects against someone deliberately trying to hack into a wireless system and prevent its ability to do an e-stop. It also safeguards against the possibility that part of the system could freeze or lock up. “All these elements make that single RF telegram totally incorruptible,” says Stagg.
Free at Last
With wireless communications having safely freed operators from the constraints of going to a fixed station or carrying a cable connected to a stop button, workers now can go about their tasks with an e-stop switch that doesn't hinder or delay their ability to respond to an emergency.
“The e-stop switch is really a device of last resort,” Stagg says. “The wireless technology enables operators to respond instantly wherever they are. It increases speed of response and reduces the risk inherent in hard-wired alternatives.”
As an example, Stagg cites a global theme park group that is using Laird wireless communication devices with Rockwell Automation e-stop pushbuttons on a number of their rides. “The crew who loads and unloads the guests onto the roller coasters and theme rides all carry one of these Laird CattronControl hand packs, and any one of them are able to stop the ride at a moment's notice,” he says.
“The guests are basically unfamiliar with the rides [from a functional perspective] and any associated risks. Typically, the parks have a lot of powerful machinery and drops in areas that people shouldn't get to; but if they wander away from where they're supposed to be, any crew member can shut down the ride immediately and put it into a safe state so no one is injured.” he adds.
From the company's perspective, the risk is not only to the individuals and the equipment, but also to the theme park's brand.
“Until recently, no one had the understanding that you could do these e-stops safely from a wireless device,” says Scott Lordo, vice president of technology at Laird. “The realization that the technology is now proven is driving a great deal of interest in these systems.”
Lordo also notes that the system has to be reliably deployed to be effective. “Some e-stop systems may be fail-safe, but you don't want shutdowns to occur all the time,” he explains. “Reliable deployment prevents productivity loss and disruption of operations, and there's a lot of work involved in making sure the system is safe but not shutting off precipitously.”
“That's one of the hardest things to achieve,” Stagg says. “The deployment imposes restrictions to make sure the RF communications is available, regardless of the situation, because it is critical that the shut down occurs under any fault condition.”
Rockwell Automation Encompass Product Partner Laird, based in Warren, Ohio, designs and supplies globally compliant, high-reliability, wireless remote control systems. This includes the CattronControl line of wireless communications products, compliant with EN ISO 13849-1, Performance Level D. The devices feature a Category 3 system structure for full redundancy.
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