Machine safety has seen a lot of changes in the past few years. Once considered a circumscribed and relatively simple matter, that’s no longer the case.
“Historically speaking, machine safety systems in the industrial automation market have been comprised of individual components such as electromechanical safety relays, safety interlocks, safety switches, fencing, light curtains and safety mats,” says Richard Gibson, product manager for ABB Jokab Safety.
But this component-based approach is no longer enough, Gibson says. “It must be understood that the machine safety components are merely some of the tools needed to achieve a successful machine safety system,” he says. “The components themselves are not the end result. There needs to be an overall goal set, assessment of what is needed, and a strategy created to accomplish it.”
Gibson is signaling a veritable sea change in the traditional approach to machine safety, a move away from yesterday’s on/off, go/no-go paradigm toward a functional approach that looks at all of the safety-related parts of the protective and control systems and seeks to ensure that they function correctly and respond correctly in the event of a fault. He’s not alone. The systems-based, functional approach is now the consensus among safety experts. In large part, that’s because of the interactive, push-pull relationship between changing market demands and evolving technology.
“The rapidly changing nature of today’s markets drives automation users to demand machines with higher speeds, faster changeovers and reduced downtimes,” observes John D’Silva, factory automation, Siemens Industry Sector. “Advancing technology, especially innovative solutions with digital technology, enables that to happen.” The safety systems are an integral part of these innovative solutions, he adds. They both call for and permit greater flexibility than was provided by the traditional perspective.
The practice of zoning is a case in point. This is the ability to safely control speeds, motion and torques in targeted sections or zones of machines or lines for maintenance or changeover without stopping the entire line, and to cycle devices such as robot arms at controlled speeds and torques. Consequently, the system can be safely slowed rather than e-stopped and restarted, typically resulting in less downtime and less lost production.
Key standards
Just because something can be done doesn’t mean it will be done safely. That’s where standards come in. The overarching standards for all U.S. businesses are the regulations promulgated by the Occupational Safety and Health Administration (OSHA), as these have the force of law. OSHA regulations, however, are too broad and generalized to be of much help to manufacturers navigating the complexities of advanced safety and control technology. Of more relevance here are the consensus standards—those adopted by organizations such as the International Organization for Standardization (ISO), the Robotic Industries Association (RIA) and the American National Standards Institute (ANSI). These contain the level of detail needed, and can serve to show compliance with OSHA mandates.
“Until recently, a safe torque off (STO) and safe stop 1 (SS1) function was sufficient for most applications,” says Tom Jensen, program manager, OEM business development, Lenze Americas. “However, the trend towards increased functional safety in electrical drive and automation technology has gained traction.” He notes that newer standards like EN ISO 13849-1 and EN IEC 62061, which both address issues of functional safety, lead engineers through this new reality.
Other standards might also come into play. For the packaging industry, ANSI/PMMI B155.1 2011 (Safety Requirements for Packaging Machinery and Packaging-Related Converting Machinery) is central. This applies to new, modified or rebuilt industrial and commercial machinery that performs packaging functions. For robotics, the key industry-specific standard is the revised ANSI/RIA R15.06-2012 Industrial Robot Standard. Both these standards largely adopt the functional safety approach of EN ISO 13849-1.
EN ISO 13849-1, which in December 2011 replaced the old EN 954 standard, governs safety functions in machine control systems. It is comprehensive, covering all safety-related components in all types of machines regardless of whether they are electric, pneumatic, hydraulic or mechanical, as well as all stages of a machine’s life, from design through operation to decommissioning. This standard and EN 62061 (Safety of Machinery – Functional Safety of Electrical, Electronic and Programmable Control Systems) are key components of the European Union’s Machinery Directive, compliance with which is mandatory for anyone wishing to sell machines in the EU.
Risk assessment
“Regardless of whether an engineer chooses to work in compliance with EN ISO 13849-1 or EN IEC 62061,” Jensen says, “probability calculations are now required to verify the reliability of the safety-related parts of machine controls.”
The most important of those probability calculations is the risk assessment, or analysis. This is a standardized procedure for determining the level of risk presented by a machine or a system and its components, followed by a risk reduction phase for minimizing or eliminating those risks.
This is a prime example of how the new standards are influencing machine design—most safety professionals would say for the better. However, skeptics often point out that risk assessment—an admittedly cumbersome process—is not required by law in the U.S. Still, for anyone wishing to sell machinery to Europe, or to the multinational corporations now insisting that all of their equipment comply with these new standards, it is mandatory.
The risk assessment/risk reduction process detailed in the new standards goes hand in hand with the validation process laid out in EN ISO 13849-1, a process of analysis and, in some cases, testing. The validation team should be independent of the design team, but that doesn’t mean the validation team waits for a finished design to be handed to it. Both common sense and the standard itself call for validation to be started early and, to the extent possible, run parallel with design. This helps correct potential problems before they become real ones. The stringent documentation required in the validation process often proves to be a useful tool for the design team.
This risk reduction process is clearly an aid to safe design, but traditional safe design practices are still key. Things like eliminating or minimizing pinch points, minimizing entanglement zones, and guarding against electrical hazards remain important from both operational and legal standpoints, regardless of what standard is employed. It’s important, too, to realize that, in the U.S. it is the machine user not the machine builder who is ultimately responsible for safety, therefore the user must make his safety needs clear to the OEM. Users need to contractually define what standards are to be adhered to, what documentation is required, and what additional safeguarding is needed.
The component revolution
The safety components Gibson spoke of—things like fencing, light curtains, safety mats and optoelectronic sensors— though not a substitute for a safety strategy, can be a valuable addition to one. This is particularly true since safety devices, like other modern industrial equipment, have benefitted from advances in digital technology.
But don’t simply buy the latest and greatest when it comes to safety components, cautions Mike Carlson, safety products marketing manager for Banner Engineering. “Over the years, the varieties of safeguarding devices have rapidly grown into a multitude of solutions,” he says. “Unfortunately, many of the latest technological solutions have proven to be cumbersome, difficult to maintain, and expensive, resulting in a questionable return on the improvement to machine safety.”
Among the classes of safety equipment effectively bringing new capabilities and enhanced protection are optoelectronic devices such as safety cameras and laser scanners. Unlike photoelectric sensors, which monitor a point or a line in space, safety cameras can monitor a relatively large volume in two or three dimensions. Because they are programmable, detection zones can be set at the controller or PC and modified to allow for “muting,” similar to zoning, to keep operators safe while maintaining optimum productivity.
Safety laser scanners are getting both smaller and smarter, notes Aaron Schulke, product manager for Sick. They combine these virtues with simple operation and flexibility, he says, “with the added potential for remote diagnostics and troubleshooting as well as performing safety control logic for the customers’ entire safety system.”
Networked scanners can provide access to the status and diagnostics of the application “locally at the end-user location for faster troubleshooting and minimal downtime, or remotely to the OEM’s support team,” Schulke says.
The rapid maturing of wireless technology in particular is providing new possibilities. “E&I (electrical and instrumentation) engineers can access their asset maintenance application from anywhere in the plant using a laptop,” notes Soroush Amidi of Honeywell Process Solutions. “But carrying a laptop is not very efficient. Therefore, vendors are developing apps that will be optimized for mobile devices so that asset maintenance vendors will have access to a field instrument’s diagnostics information from their handhelds. These diagnostics will also be enhanced to include wireless network diagnostics in addition to the existing field device diagnostics.”
People, the ultimate technology
The fact remains that people sometimes use safety technologies haphazardly, or feel that the unwritten rules of their organization call for disregarding safety if it seems necessary to keep production at optimal levels.
Donna Rae Smith, CEO of the behavioral strategy company Bright Side, has seen this many times and has some thoughts about its non-safety implications. “If workers feel encouraged to disregard ‘official’ safety policies and procedures to reduce maintenance time or increase throughput,” she notes, “they’ll likely feel just as flexible about other company policies and procedures.”
A cavalier attitude toward safety not only affects the well-being of plant personnel, but correlates with plant performance as well, agrees Steve Ludwig, safety programs manager for Rockwell Automation. “Best-in-class companies regard safety as a core value and productivity driver, not a burden,” he insists. “Looking beyond the makeup of a company’s safety programs and examining the larger trends of the best performers can provide valuable insights into what can be accomplished when safety is implemented holistically, with consideration to a manufacturer’s larger operations.”
Ludwig cites work by the business research firm The Aberdeen Group, which found that the companies that were the top performers in addressing safety in three key areas—culture (behavioral), compliance (procedural) and capital (consisting of investment in, and quality of, the safety equipment deployed), what Ludwig calls the three Cs—achieve 5-7 percent higher operational equipment effectiveness, 2-4 percent less unscheduled downtime, and less than half the injury rate of average performers. “These higher-performing companies also experienced far fewer workplace accidents compared to average performers—1 in 2,000 employees vs. 1 in 111 employees.”
Ludwig and Rockwell have fashioned these results into an analytical tool they call the Safety Maturity Index (SMI). This index, Ludwig contends, can give manufacturers visibility into their safety programs and the ability to optimize them using the three Cs. He summarizes the philosophy behind the tool this way: “Plant-floor safety has long been viewed as an onerous and costly obligation that adds little value to overall operations. In many companies, safety has been viewed as a productivity drain. Today, best-in-class manufacturers realize that the combination of employee behavior, processes and procedures, and technology implementation enable them to go far beyond simple compliance to deliver improved productivity, greater efficiencies, and dramatically lower injury rates.”
Help in Navigating the Safety Landscape
Industrial machine safety has gotten more complex in the past few years. Fortunately, there are numerous aids to help in navigating the new safety landscape. Here are a few.
- OSHA’s eTool website has interactive, training tools on occupational safety and health topics. Check http://awgo.to/132 and http://awgo.to/133.
- A good source for safety standards is ANSI’s search engine at www.nssn.org.
- For the packaging industry’s ANSI/PMMI B155.1 2011 (Safety Requirements for Packaging Machinery and Packaging-Related Converting Machinery), users can check PMMI’s website (www.pmmi.org).
- For information about the Robotics Industry Association’s ANSI/RIA R15.06—2012 Industrial Robot Standard, see the organization’s website at www.robotics.org.
- Banner Engineering has a handy, non-product-specific website concerning machine safety called iKnow Safety at http://awgo.to/134.
- Both Siemens (www.usa.siemens.com/industry) and Rockwell (www.rockwellautomation.com) offer classes in safety. For information on Rockwell’s Safety Maturity Index analytical tool, go to http://awgo.to/135.
- Information about Festo’s Machine Safety Resource Guide and more can be found at http://awgo.to/158.
- Download Sick’s Guidelines for Safe Machinery at http://awgo.to/159.
