A Quiet Revolution in Robot Safety

Safeguarding solutions for robotics are often burdened by designs that rely on a worst-case analysis for both the reach of the arm and stop times.

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This results in much larger perimeter guarding than is often necessary, decreasing productivity and increasing the required production area on the factory floor. However, manufacturers are changing the way they evaluate and deploy safeguarding systems to create safe environments for production workers, while also increasing access to the production process.

The latest approach is to base the safeguarding strategy on a task and associated hazard analysis and implement the safeguards in robotic programmable safety systems (RPSSs), rather than in separate safety programmable logic controllers (PLCs). This spurs a quiet revolution in safety policies and associated safety systems.

Most notably, robotic suppliers are introducing innovative solutions that provide protection from the "inside out," rather than the traditional "outside in" approach. This has the potential to bring huge benefits by reducing the amount
of floor space required for industrial robots and by simplifying safeguarding solution implementation.

Robotic automation suppliers now offer a new generation of safety solutions designed to be more effective in preventing accidents, less costly to implement, easier to adapt, and more reliable than existing hard-wired systems. Here, a "designed-in" safety approach provides an opportunity to improve the productivity of the work cell by constraining the movement of the robotic arm based on the location of the production worker and the perimeter fencing. New RPSSs, certified according to EN 954-1 Cat 4 risk assessment levels, facilitate this shift. These systems operate separate, but integrated safety solutions that are closely coupled with the robotics controller. To comply with the EN 954-1 Cat 4 risk levels, these systems use dual-redundant processors to ensure the required reliability.

ABB, Fanuc and Kuka Robotics all have programmable safeguarding solutions that function as watchdogs to the robotic controller. Each implementation varies slightly, but one element they all have in common is direct access to the robot controller, application programs, coordinate systems, dynamic speeds/accelerations and trajectory planners. Even safe stopping distances can be defined dynamically with access to the robotic controllers.

Access to the robotic controller internals makes it possible to constrain the robotic motion precisely for the application. Where light curtains and fencing generally create cube shaped boundaries, these solutions are able to define working envelopes with more generalized surface boundaries. Further, they also prevent any ill-defined robotic application programs from moving outside of the defined safe envelope.

Robotic programmable safety systems directly interface to traditional safety devices in the robotic work cells. Previously, the safety PLC had made inroads into the robotic work cell market because of its flexibility and ability to interface to a wide range of safeguarding devices such as light curtains, laser scanners, safety mats, interlocks and operator switches. In addition, the safety PLC provided the capability to easily reconfigure the safety strategy. However, the safety PLC can only signal the robot controller to stop the motion once an operator is detected in the working envelope. In contrast, a RPSS provides new limits to the robotic application to prevent the robotic controller from making moves outside of a safe zone.
 
Next step?

Increasingly, more automation platforms support robotics capability in conjunction with general-purpose motion control (GMC). Machine builders working with the latest generation of automation technology are able to rapidly innovate and integrate functionality that once required separate controllers. Is the next step for these solutions to integrate a more advanced RPSS similar to that offered by the major robotic suppliers? Many of these systems already incorporate a commonly accepted solution for safety PLCs. However, these solutions continue to function independently of the other control functions.
 
As robotics increasingly move into the consumer goods packaging industry for both primary and secondary packaging lines, the issue of robotic safety will become critical. Limiting the robotic envelope will enable manufacturers to keep production moving without having to shut down the packaging lines completely while the operator is inside the working area.

Sal Spada, SSpada@ARCweb.com, is a Research Director at ARC Advisory Group Inc., in Dedham, Mass.

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