How to improve the safety of an operating machine beyond just an e-stop button

Red, yellow, green and blue are standard stacklight colors. But a variety of other colors can be used to indicate specific conditions and needs.

Aside from an e-stop button, what other buttons, alarms, stacklights or switches can be used to improve the safety of an operating machine?

Robb Weidemann, senior business development manager, lighting and indication, Banner Engineering: For safety applications, it is important to conduct a risk assessment and utilize safety-rated devices, such as e-stops, to prevent the risk of injury. That said, there are many non-safety-rated devices, including indicator lights and buttons, that can be bundled together with a safety system to provide an intuitive and ergonomic interface for operators. For example, sometimes operators will need to enter a robotic cell during a work cycle. Shutting off the robot with an emergency stop button, while sometimes necessary, will bring operation to a sudden halt that can damage the robot and materials being worked on. Instead, with an illuminated operator selector switch, the operator can bring the robot to a controlled stop. The illuminated base turns from green to yellow when the movement of the robot has stopped, providing a clear indication that the operator can enter the cell.

Tom Rosenberg, vice president of marketing and engineering, Balluff: As our automation systems become more collaborative, additional guidance is required to ensure machines do not go into full stop or even slow down due to humans unknowingly encroaching in a safety zone. Again, this is where the continuously variable information displayed on a stacklight or indicator can significantly improve the process. For instance, when an operator enters a safety zone monitored by an area scanner, stacklights or indicators can display just how far into the zone they are. As the operator moves deeper into the zone, the variable indicator can signal the encroachment in real time. The operator can visibly see that they are causing a potential slow down and get out of the area before a full stop occurs.

Alex Dzatko, proposals specialist, process automation, Pepperl+Fuchs: Buzzers and horns are devices that would be suitable to improve the safety of operating machines. There are many buzzers and horns available for most any application, from ATEX/IECEx Zone-1-rated 30-mm, illuminated buzzers to general-purpose and class/division-rated electronic horns. These devices can be installed on the door or on top of control panels, or they can be located in appropriate places around the plant-floor machinery.

Alvaro Sanchez, product manager, Rockwell Automation: In addition to e-stops and indicators, there are a wide variety of machine-safety products that help to protect personnel, machinery and the environment while maximizing uptime and enhancing productivity. These products include safety light curtains and laser scanners, interlock switches and pressure sensitive safety mats, among others.

Danny Weiss, senior product manager, Newark element14: As plant operations and distribution centers become more automated, there are fewer people standing next to every machine. Conveying information quickly and in the best format helps productivity. For example, a stacklight conveys information such as material shortage in a bin particularly well. Stacklights also help maintenance people quickly identify problem areas and machine status, whereas detailed fault information, past alarms for machine troubleshooting, machine runtime is best conveyed with the HMI. Fewer people often mean that conveying information quickly is the key to productivity and machine uptime.

Michael O'Neill, sales manager, Werma-USA: It’s a visual world, and communication is key, so much so it is an important part in any lean-principles program. For this reason stacklights are offered with a variety of light effects: permanent; blinking—viewed within one’s peripheral vision; rotating; flashing—getting attention outside of one’s peripheral vision; random flickering—to overcome one being acclimatized to the flashing effect; ultra-bright for bright ambient areas.

Peter B. Gasparini, sales manager, Werma-USA: A client had a fabric-cutting machine with several processes, so the yellow LED flashed during this process to alert the operator not to go anywhere near blades/cutter. Or light with alarm simultaneously activated during a potentially dangerous process.

Todd Mason Darnell, Ph.D., marketing manager of services and safety, Omron Automation Americas: One of the keys to improving safety is improving the situation awareness of the operators and plant personnel. Adding flashing/illuminated reset buttons, request to access buttons, door-open alarms and audible alarms, including music and melodies, all help to create worker awareness of the status of the machine. We also recommend as a best practice, and it is required by in ANSI B65-1 for the printing industry, that larger equipment or equipment with multiple operators have a machine start alarm to alert everyone before the equipment starts to operate.

Steve Olson, IIoT technical specialist, Hilscher, member of Control System Integrators Association (CSIA): Light curtains, safety switch mats and proximity motion sensors can be used.

Michael Doebelin, Advanced Engineering, member of Control System Integrators Association (CSIA): Typically a risk analysis has to be in place. Traditional e-stop buttons, rope switches, light curtains, area scanners and safety lockable gates with feedback are a minimum. More and more devices feature safe torque off.

Carter Williams, product manager, Siemens: There are several products that can be used to improve safety of an operating machine. First, stacklights, aka signal columns, are used in any application that requires visual or audio signaling to inform workers and/or visitors of their environmental conditions. The signaling can be used to monitor process control of their machinery by letting them know when a machine is running, turned off or down for maintenance; to provide plant safety information to workers by letting them know when it is safe to enter a restricted area or not; to provide an emergency evacuation notice to the plant area—strobe lights and sirens/buzzers are often used together.

Second, a switch could be used to turn the application off and on, such as an HOA switch. An advanced application using a switch would incorporate a keyed switch that would only allow authorized personnel to access and control the machine; an RFID-keyed switch that provides authorized keyed control access to a machine by job levels to provide not only a measure of security/safety, but also provide overall equipment effectiveness (OEE).

For example, the operator is given a color-coded key that allows for the machine to be turned on and off. Maintenance personnel are given another color-coded key that provides another level of access, and finally the supervisor is given a key that allows complete access.

In addition, the RFID switch provides controlled access if it is connected over the customer’s network and it can provide information about the machine’s productivity. Further analysis of this data can become a gateway of information to increase productivity.

Trey Gantt, product manager, Eaton: This category of controls includes a wide range of pilot devices to support operation, control and protection that rated for global applications. Devices include pushbuttons, indicator lights, selector switches, actuators, joysticks, palm switches, control stations and more.

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About the author: Mike Bacidore

Mike Bacidore is the editor in chief for Control Design magazine. He is an award-winning columnist, earning a Gold Regional Award and a Silver National Award from the American Society of Business Publication Editors. Email him at [email protected].

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