Robot Safety

The need to keep factory workers safe from errant robots-and vice versa-is driving the development of standards and the integration of ancillary equipment into robotic cells.


Companies Mentioned
Posted on Nov 03, 2006

John Deere & Co. (Moline, IL) has deployed about 80 different robots at its Horicon, Wisconsin, factory where they are used for welding and painting the tractors manufactured there, as well as for material handling. Robot automation has made the manufacturing site more efficient and productive, but it has also introduced new risks. A robot can be big, it is definitely strong, and while some operators may consider a robot just another team member on the job, let's face it: it's a machine. That's why, in the early 1990s, Thomas Tabaska, then a robot support specialist at John Deere, was asked by his boss to make sure the robots pose no danger to factory personnel. Now, as the lead advisor on robot safety and a quality manager, Tabaska has implemented a corporate strategy that covers everything from creating a physical barrier around a robot cell, to integrating safety controllers into the machine, to deploying safety devices that will detect a potentially hazardous situation. He's dedicated years toward helping everyone in the company understand how to avoid close encounters of the robot kind. And Tabaska is not alone on his safety endeavor. The automotive industry, which is very dependent upon robots, is putting safety at the top of its priority list, according to industry observers. As other industries look to add robot technology to the production cycle, safety is factored in as part of the complete solution. Perhaps it is because manufacturers are becoming more sensitive to work conditions. Or, perhaps it is because, as companies become global conglomerates, the more stringent safety codes in Europe must now be applied to all worldwide factory sites. Or, maybe it's just another way to avoid lawsuits associated with accidents. Whatever the impetus, there is nothing wrong with going the extra mile to protect employees. "People may not always realize that they are around dangerous equipment," says Tina Hull, an application engineer at Pilz Automation Safety L.P. (Canton, MI), a leader in developing safety tools for robots. "If a robot comes at you at full speed, it has a good chance of killing you." And, unfortunately, robotic accidents do happen and are usually fairly gruesome, says Dick Slansky, a senior analyst at ARC Advisory Group (Dedham, MA). "They usually involve some large articulated arm or some mass, and the human gets crushed or whacked." Case in point: in 1999, a carousel operator at a meat packing plant was killed when his foot tripped a light sensor causing a computer-controlled robotic platform to come down from above, crushing his skull. In a separate incident at another company, an operator of an automated die-cast system died after being pinned between the back end of an industrial robot and a steel safety pole. These accidents are reported by the Occupational Safety & Health Administration (OSHA) and are cited with explanations of corrective action (see www.osha.gov/SLTC/robotics/index.html). The problem is, however, that OSHA will typically come in to review a situation only after an accident occurs or when complaints have been filed. So manufacturers are taking it upon themselves to implement preventive measures and thus avoid industrial accidents altogether. To do that, they are looking to industry standards for guidance. They are also counting on robot makers to adhere to safety standards and incorporate certain technologies-such as safety programmable logic controllers (PLCs) or safety buses-that ensure redundant protection is built-in. They are also applying several layers of devices around the robot cell, ranging from safety relays to safety curtains to safety mats. Above and beyond the personal safety initiatives, companies are not forgetting to protect the robot itself. After all, it's a major investment. In that regard, vision system integration not only adds precision to the application, but also acts as the robot's eyes, avoiding situations that may impair its ability to function normally. To be clear, vision systems cannot be a part of the standards-based safety system because the regulations dictate that the safety device or system must be hardwired to the robot in order to disable the function of the machine in the event of an emergency. Vision systems are connected only via a software program, so it is not an adequate intervention method when it comes to protecting humans. "But machine protection is a realistic thing that can be done with vision," says Mark Sippel, product marketing manager for vision and bar codes at Omron Electronics LLC (Schaumburg, IL). "Even in the most simplistic sense, you can teach it to look for a given part, and if something else comes down the line, a photoelectric sensor could trigger the vision system, feeding that [information] back to the robot." Omron makes the F210 and F250 series of vision systems that include an "if-then" function. The vision systems look at a situation under the directive of the if-then statement: "If this, then do that; if not this, then start this routine." Cognex Corp. (Natick, MA) also has vision systems that feed data back to the robot. And the company has worked on providing protocols that can talk with different buses and PLCs, so that the vision system can trigger an alarm, officials say. But Cognex is taking vision a step further. The company recently identified safety and security outside of the robot cell as a new area of exploration with the introduction of its new "people sensor" (see sidebar, page 20). Vision systems that are high-speed, high-resolution, and can handle color applications are now small enough and affordable enough to integrate into the robot workspace, which could open the door to new types of safety and security applications around the robot cell itself. "Theoretically, it would be possible to use vision to determine if something is in the robot workspace that shouldn't be there," explains Phil Heil, applied engineering manager at DVT Corp. (Norcross, GA). "However, there are still issues to overcome. Normally, single-camera systems don't have a way to determine distance without special structured lighting. The other problem is setting up the system to accommodate all of the possible 'good' scenes while determining if something is amiss." Therefore, when it comes to operator safety around the robot cell, light curtains and safety mats are the best security device, Heil notes. John Deere's Tabaska uses light curtains to protect some of the robot spaces. A light curtain shines a beam which, if broken due to someone entering the area, causes the robot to shut down. Other devices that can guard an area include the traditional physical barrier and cage. Another option is the safety mat, which senses the presence of someone or something within the protected area. Many sensor companies, like Omron, Keyence Corp. (Woodcliff Lake, NJ), Banner Engineering Corp. (Minneapolis, MN), and SICK Inc. (Minneapolis, MN), for example, are extending their offerings into the safety device arena, which is turning into a big market for these companies. "It makes good business sense to have these types of devices," says Mike Frey, Omron's safety product marketing manager. A light curtain costs a couple of thousand dollars to buy and install, he says, but compare that to what it would cost a company in OSHA fines, lawsuits, and emotional distress if someone were to get hurt because that safeguard was not in place, and the device more than pays for itself. While these added accessories are the responsibility of the end-user to implement, customers are increasingly turning to their robot suppliers to build more safety precautions into the systems. For example, Kuka Roboter GmbH (Augsburg, Germany) incorporates the SafetyBUS p interface from Pilz into a centralized safety controller function. The SafetyBUS p is a remote I/O based on the controller-area network (CAN) protocol, allowing inputs from multiple safety devices including emergency stops, light curtains, safety gates, etc. Siemens AG's (Munich, Germany) Automation & Drives group has a similar bus system called PROFIsafe. And Rockwell Automation (Milwaukee, WI) is currently working with Omron and SICK under the ODVA (Boca Raton, FL) to design Common Industrial Protocol (CIP) Safety, an open protocol for safety communications across disparate networks. The goal is to provide fail-safe communications between safety interlock switches, light curtains, and safety PLCs. Robot makers can build safety PLCs into the system, but that is basically about incorporating a separate hardwired control system for redundancy. "What they're really doing is assuring that the safety devices out there will work properly," explains Bob Frease, staff engineer at FANUC Robotics America Inc. (Rochester Hills, MI). "They are not really making sure the robot is safe, but making sure the devices that the robot is talking to around it will work properly." While FANUC supports these extra controls and safety components, the real assurance it can offer to its customers is compliance with the Robotic Industries Association's (RIA; Ann Arbor, MI) R15.06-1999 standard. The RIA, a trade association made up of manufacturers and users, is hosting its 15th annual Robot Safety conference later this month in Cincinnati, Ohio. "There are installation criteria and safeguarding that don't necessarily come with the robot," says Jeff Fryman, director of standards development for the RIA. "The standard goes into detail on how a robot needs to be used in an industrial setting to be a safe worksite." The RIA standard comes under review next year (as part of the customary four-year review cycle). But it is so complete that even the new Canadian safety standard, dubbed CSA Z434, is based almost entirely on the 15.06, says Fryman. This inches the robot industry closer to having a North American safety standard, but there really needs to be an international standard in order to alleviate confusion among the many guidelines now available (see sidebar, above). "The robot companies want to make sure they're conforming to the safety standards," says ARC's Slansky. "It's not even a matter of differentiation; they will be required to do this." Indeed, it is the end-users that are requiring the robot suppliers to comply. That's why Tabaska of John Deere participates in the RIA group that defines the standard. "You need to make sure that cell is 100% safe on the third shift at two in the morning when supervision isn't around," says Tabaska. "That's when people take shortcuts and don't have full accountability." MA

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