by Joseph J. Lazzara
The evolution of global safety standards, the impact of ever-evolving new technologies and the desire to improve workplace safety records are major forces that continually drive improvements in integrated machine safety design. What are some of the key future trends in machine safeguarding that will significantly impact the machine and automation markets? What will change the shape and practices of the machine guarding industry? Well, turn down the lights, get out your crystal ball, unwrap your Ouija board and let us examine what the future may hold...
Globalization of U.S. Standards
U.S. machine builders are often faced with the rather daunting task of designing equipment to meet U.S. standards such as those of the National Electrical Code, OSHA and American National Standards Institute (ANSI) for the domestic market, and international standards, such as EN, ISO and IEC, for the export market.
The historic differences between these standards can be as significant as the type of control systems, emergency stops, selection of safeguarding, or whether the safeguarding is standard or customer-added equipment. Other differences can include seemingly minor but aggravating variants such as the acceptability of wiring color codes. Fortunately, the globalization of U.S. standards, leading to the pursuit of common, international standards for machine safety, will provide some relief for the tormented machine tool designer.
One example is NFPA 79, The National Electrical Standard for Industrial Machinery. The most current edition, 2002, underwent major revisions to align it more closely with IEC 60204-1, Electrical Equipment of Machines, the international electrical standard, including formatting changes so the two documents are easier to review and compare. For example, sections 5.3.2 of NFPA 79-2002 and 60204-1 1997 both describe requirements for an electrical supply circuit disconnection device. Further alignment efforts to European requirements for the 2006 edition of NFPA 79 are planned.
Further evidence of the trend toward the globalization of U.S. standards can be seen in the newest revisions of ANSI B11.19-2003, Performance Criteria for Safeguarding, where the influence of certain international standards, such as IEC 61496, Electrosensitive Protective Equipment, and EN 999, The Positioning of Protective Equipment In Respect of Approach Speed, is evident. B11.19 covers a broad range of topics and does not have an exact equivalent international standard, where the topics were separated into many distinct standards, with varying revision levels.
The robot safeguarding standard, RIA 15.06-1999, American National Standard for Industrial Robots and Robot Systems Safety Requirements, was revised with influence from ISO 10218, Manipulating Industrial Robots Safety, which is now being revised again to align closer with RIA 15.06. Perhaps this is truly an example of "harmonic convergence" in the world of standards!
Europe is still ahead on the standards effort, as the United States is typically harmonizing more to existing European standards. Of course, the transition from U.S. versions to more international-centric standards can give the European machine builders a jump over their U.S.-based competitors. Nevertheless, this globalization trend is positive for the U. S. machine tool builders, as without it, they could be faced with the dilemma of continuing to manufacture separate domestic and international versions of their products, or abandon the international market altogether.
More Sophisticated Safety Controllers
Next we will see the wider adoption and greater sophistication of safety controllers, which include such devices as safety relay modules, relay-controller hybrids, safety PLCs and specific function safety controllers, such as a muting controller.
Electromechanical safety relay modules have been the backbone of safety control design for decades. They are simple to use, easy to retrofit to existing machine control panels and offered with an acceptable cost structure for small to mid-range installations. The products are available with a wide variety of functions and output selections, covering everything from emergency stop relays, monitoring interlock switches on guards and gates to two-hand controls. The safety relay modules have been increasing in sophistication; some are now offered as fully electronic units and could hardly be called "relays." These offer more programmability, but sacrifice voltage isolation and higher switching current capability.
The next step up in the quest for more intelligent safety controls are the relay-controller hybrids, often described as modular controllers. These are simple controllers with relay or electronic-based expansion modules. Programming can be as sophisticated as using PC-based software or as simple as using a screwdriver to set selector switches, depending on the system approach. These hybrids fill the gap between the safety relay modules and the more complex safety PLCs. These products are typically used in mid-range applications, or as subsets in more complex installations.
For installations requiring more demanding programming needs, such as complex machine controllers and configurations, the trend is to use safety-rated PLCs. These devices contain the fail-safe software required for critical safety functions and can take direct inputs from most safety products, such as light curtains, emergency stops and mechanical interlocks. From STI's perspective, our new safety light curtains and safety mat controllers are available with solid-state outputs. These outputs are very convenient and cost-efficient, especially when the light curtain is connected directly to a safety-rated PLC, thus eliminating the need for intervening safety relay modules.
Care is needed to ensure that the safety PLC system programming has been thoroughly reviewed and tested so no loss of safety function can result. Users should not be able to alter this programming. The trend for safety PLC systems use will be in the mid-range to complex applications.
Safety-Rated Buses and More Intelligent Safety Devices
The next industry trend will involve the use of safety-rated communication buses or networks. The emergence of these safety control networks will have a major impact in the further integration of safety and machine controls into one seamless system.
In order to examine the advantages of the safety networks, first, we must understand how safety devices are typically installed. Usually, they are individually hard-wired or, alternately, "daisy-chained" in series back to an emergency stop control, a safety relay module, safety controller or a machine primary contactor. Series wiring saves on installation costs but is difficult to troubleshoot. For example, which mechanical guard may not be fully latched? Where is the location of the emergency stop that was pulled? It would require extra wiring to provide this level of fault detection to the specific device.
The beauty of the safety-rated control network is that with less wiring, and hence much reduced installation costs, a specific device can be identified and the problem diagnosed. The exact location of that pulled emergency stop along 200 feet of conveyor can be readily detected by an information display. With the use of a network cable, usually wired in series with the devices, the bus communications allow for the transfer of status and diagnostic information, as well as safety-critical control data. This saves costs in design, materials and installation. The increased intelligence and diagnostic capability translates into less machine down-time and, therefore, higher productivity.
Safety networks have integrated the safety and control system as one common unit there is no need for a separate safety bus, or a separate safety PLC. A specialized bus safety controller, or a PLC outfitted with a safety control network module, may be sufficient, depending on the complexity of the system and the number of devices.
As we have seen with the safety controllers, the safety networks also are available with various levels of sophistication, speed and expandability, depending on the complexity of the applications. AS-Interface bus, sponsored by an international (although primarily European) consortium, has a safety-rated bus configuration, which is called "Safety at Work." AS-i stands for actuator-sensor-interface. Both safety and non-safety devices can be included in a single AS-i network. Positioned for small to mid-range applications, AS-i can accept up to 62 non-safety devices or up to 31 safety devices.
Two other safety solutions, with more capability and higher speeds, are ProfiSafe and the proposed CIPSafety protocol. These systems would be more suited for mid-range to complex installations. All three of these safety buses were adopted from existing control networks, with the safety functions added on through extended system architecture and hardware.
If these safety networks are now available, why is this considered a future trend? Quite simply, the transition to adopt these more advanced systems, especially in the United States, has been slow, aggravated by regulatory standards that can appear outdated and also by the lack of applicable devices. For example, the 1997 version of NFPA 79 was the primary barrier to adopting safety networks for machine control use. This obstacle was corrected in the 2002 edition of NFPA 79, where software-based controllers, which met specific criteria, were allowed to perform safety-related functions.
The use of a safety bus requires more intelligent safety devices with capabilities beyond the simple on/off or open/close outputs. Machine designers should expect the availability of these safety bus connection devices to grow. Safety devices such as interlock switches, emergency stop push buttons and light curtains are available with the appropriate bus communications protocol and thereby provide improved diagnostics.
Greater Use of Machine Specific Safety Devices
A future trend that is just emerging involves the design of a safety device for one specific type of machine. This is very different from a general-purpose safeguard, such as a light curtain, safety mat or interlock. These products are readily used on many different types of machines, such as robots, mechanical power presses, lathes, mills and shears.
With this new trend, a device is machine specific, not machine independent. One such example is the new, moving ram type of optical safeguards specific to the hydraulic press brake, such as the LazerSafe from STI. Used for making precise bends in sheet metal, hydraulic press brakes are notoriously difficult to guard. By their very nature, they are versatile machines, which may often require the operator to work close to the point of operation, depending on the size of the work piece and the type of bend required. LazerSafe's optical transmitter and receiver mounts on the moving ram of the press. A 40mm wide, flat band of laser light is projected under the tool tip to provide protection to the operator. Ram speed and stopping distance are continuously monitored by the LazerSafe controller through transducer feedback, maximizing the safety and throughput of the press brake and facilitating increased use of the high-speed mode of the press. The results are significant increases in productivity and enhanced safeguarding, clearly a win-win situation and not uncommon when safeguarding design can be optimized for a specific use.
More Formal Risk Assessments/Risk Reduction
The next trend involves a more formal risk assessment and risk reduction program. There are two fairly recent standards, which espouse the advantages and methodology of risk assessment. By performing such an assessment, companies can determine where best to focus their efforts to reduce those risks.
The most recent U.S. robot safety standard, RIA 15.06-1999, American National Standard- for Industrial Robots and Robot Systems Safety Requirement, is a good example. The other is ANSI B11.TR3-2000, Risk Assessment and Risk Reduction A Guide to Estimate, Evaluate and Reduce Risks Associated with Machine Tools, which describes a process for employers to use in assessing the risk of such injuries in their workplaces. Recently, the National Institute for Occupational Safety and Health (NIOSH) announced a project with business, labor and insurance industry partners to evaluate the effectiveness of an ANSI voluntary guideline to prevent such injuries.
The TR3 Committee has taken a somewhat different (and they believe better) approach than the European- based standards on risk assessment. There are also differences between the robot standard and the ANSI TR 3 standard as well. Unfortunately, this again means that the U.S. standards are not exactly harmonized with the international standard ISO 14121, Safety of Machinery Principles of Risk Assessment, although they are similar.
The trend of implementing a more formalized risk assessment program will help ensure that machines are designed with the safety and integrity of the machine in mind at an early stage in the machine's development. To further help the somewhat complicated task of performing a risk assessment, there are now software programs, such as DesignSafe, by Design Safety Engineering (www.designsafe.com) that can help users consider, evaluate and document the assessment.
Well, there is a sneak peak at what the future of machine guarding may hold. Until next time, be safe out there!
Joseph J. Lazzara is president and CEO of Scientific Technologies Inc. (STI), the largest provider of automation safeguarding solutions in North America (www.sti.com). He has a bachelor of Environmental Engineering degree from Purdue University and a masters in Business Administration degree from Santa Clara University. He is chairman of the Safety, Health and Environmental Committee for the Association of Manufacturing Technology (AMT). He is also a member of the board of directors of the American Electronics Association (AEA).