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New robotic safeguarding solutions make safety PLCs unnecessary

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. This results in much larger perimeter guarding than is often necessary, detracting 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 the production worker while also increasing access to the production process.

The latest approach is to base the safeguarding strategy on a task and asso ciated hazard analysis and implement the safeguards in robotic programmable safety systems (RPSS), rather than in separate safety PLCs. This spurs a quiet revolution in safety policies and associ ated safety systems; most notably robotic suppliers are introducing innovative solutions that provide protection from the "inside out" rather than the "outside looking in" approach that has been pervasive in the industry. This has the potential to bring huge benefits to manufacturing community by reducing the amount of floor space required for industrial robots and by simplifying safe guarding solution implementation.

Robotic safeguarding
Robotic automation suppliers now offer a new generation of safety solu tions designed to be more effective in preventing accidents, less costly to implement, easier to adapt, and more reliable than existing hard-wired systems. These innovations are based on the concept of "work envelope limi tations," which is more akin to a "designed-in" safety approach, than an "add-on" safety approach.

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. This shift in safeguarding implementations is facilitated by the introduction of robotic programmable safety systems that are certified according to EN 954-1 Cat 4 risk assessment levels.

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 relia bility. This parallels the approach employed by most safety PLC suppliers.

ABB, FANUC, and Kuka Robotics all have programmable safeguarding solutions that function as watchdogs to the robotic controller. Each implementa tion 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 plan ners. Even safe stopping distances can be defined dynamically with access to the robotic controllers.

The access to the robotic controller internals is where these safeguarding implementations offer the greatest bene fits because this makes it possible to constrain the robotic motion to precisely what is required for the application. Where light curtains and fencing gener ally create cube shaped boundaries, these solutions are able to define working envelopes based on more generalised surface boundaries. Furthermore, it also prevents any ill-defined robotic applica tion programs from moving outside of the defined safe envelope.

Safety PLC
Robotic programmable safety systems (RPSS) directly interface to traditional safety devices found 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 scan ners, safety mats, interlocks, and operator switches. In addition, the safety PLC provided the capability to reconfigure the safety strategy without having to rewire a safety panel.

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 greater flexibility, allowing it to apply new limits to the robotic application to prevent the robotic controller from making moves outside of a safe zone.

Robotic programmable safety systems may well deter growth in the safety PLC market for some safe guarding suppliers. The safety PLC market segment had been growing at nearly 20 per cent annually, primarily due to its acceptance in large produc tion lines and robotic work cells. ARC believes that the emergence of the RPSS by these major robotic suppliers will have a strong negative impact on the growth of the safety PLC market, particularly for safeguarding suppliers that have not been able to cost-effective integrate the safety PLC with their non-safety PLC platforms.

Increasingly more automation plat forms support robotics capability in conjunction with general purpose motion control (GMC). Machine builders working with the latest genera tion of automation technology are able to rapidly innovate and integrate func tionality 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 independent of the other control functions.

As increasingly more robotics moves 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 manufac turers to keep production moving without having to completely shut down the packaging lines while the operator is inside the working area.

Control platforms
Parallel robots are one of the fastest growing segments in the packaged goods market. To sustain this move toward mechatronic control platforms that provide this broad range of motion control functionality, general automation suppliers will need to provide capabilities that can compete with those now emerging from the robotic suppliers.

Business and plant managers actively seek a well thought out safety strategy that also supports business benefits such as increased productivity, improved machine efficiency and increased uptime. An “inside out” approach to robotics cell safety using robotic programmable safety systems may well provide the key to this strategy.

[Sal Spada ( is Research Director, ARC Advisory Group.]

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