Task-Oriented Safeguarding Improves Business Metrics

Machine safety in the traditional sense refers to add-on electrical and mechanical components that protect personnel from injury or death while working in or near industrial machinery.

Historically, conventional safeguarding systems emphasized absolute operator safety at the expense of productivity. However, despite efforts to make equipment “absolutely safe,” highly motivated operators seeking productivity improvements often override conventional safety systems, greatly increasing the odds of accidents. For this reason, even rigid safety solutions can’t guarantee absolute safety.

A more modern, effective safeguarding strategy is one that evaluates the use of equipment from a task-oriented perspective (i.e. how does the operator have to interact with the machinery?). This task-oriented approach lends itself to the use of an integrated system solution that relies on intelligent automation components. This minimizes the risk of operator injury to a tolerable level in specific operational modes of the machine, while allowing the operator to work efficiently compared to use of absolute safety measures such as physical guards and interlocks. For example, modern safety systems allow operators and maintenance personnel to gain access to operating machine work zones by setting programmable limits on actuator speeds, forces and torques to mitigate the risk of injury from these devices.

Justification of this modern approach to safety can be found in studies in Sweden and Japan regarding robotic accidents. The studies concluded that many robot accidents do not occur under normal operating conditions, but rather during programming, maintenance, repair, testing, set-up or adjustment. In most instances, work procedures required the operator or maintenance worker to temporarily enter the robot's working envelope, where unintended operations could result in injuries. Perimeter guarding or light curtains are temporarily overridden, exposing the worker to possible injury upon entering the work zone while the machine is still operational. In contrast, a modern safety approach respects the behavior of factory personnel and implements safety solutions that allow safe access to work zones. This approach to safety is allowing significant improvements in manufacturing productivity.

Many manufacturers have come to view an intelligent safety strategy as a competitive advantage rather than a cost burden. In addition, ensuring worker safety directly supports manufacturers’ initiatives to limit liability exposure and to improve their public images. From ARC’s perspective, modern, intelligent safety systems directly improve the bottom line.

Modern, intelligent safety solutions are usually associated with Safety programmable logic controllers (PLCs) that replace conventional hard-wired safety relays. However, far more important to productivity improvements are the avoidance of unintended axis movement, and “Safe Motion” that reduces the risk of injury to operators by allowing continued, but limited axis movement. In addition, the use of programmable safety logic greatly increases the flexibility of a safety system. Thanks to these benefits, Safety PLCs and Safe Motion have become permanent parts of modern, intelligent safety concepts.

Current safety standards allow the integration of configurable safety systems directly in servo drives. This embedded functionality in the drives makes it possible for machine builders to incorporate safety strategies that improve operator productivity. With safe drives, safety solutions are becoming less complex, with far fewer cables and connections, resulting in reduced design, commissioning and installation costs.

Recommendations

ARC recommends that manufacturers specify machinery utilizing flexible, programmable safeguarding subsystems to allow for rapid reconfiguration of manufacturing processes. Further, factory workers and unions need to be educated so they can be active participants in designing processes with intelligent safety technology, rather than just cling to a “lockout only” philosophy. Machine control architecture is very important when seeking the benefits of Safe Motion, Safe Stopping, and Safety PLCs. Be sure to use machine builders that are on the forefront of intelligent safety.

Range of SafeGuarding Solutions Expands Beyond Safety Relays

Safety PLC         
Programmable Logic Controllers rated for up to SIL 3 Level

Safe Stopping   
Servo drives and AC drives focused on Stopping safety functions in accordance with EN60204-1 without use of external safety hardware

Safe Motion       
Servo and AC Drives with the ability to incorporate slow speed modes, reduced torque, and a higher speed response in a powered safety zone.

Source: ARC Advisory Group


Sal Spada, sspada@arcweb.com, is Research Director,
Discrete Automation, at ARC Advisory Group Inc., in Dedham, Mass.
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