Robotics and safety

By Paul Stathis
Friday, 22 June, 2007

In the workplace, safety can't be traded off for commercial benefits, even though safety facilities can have commercially detrimental implications. Less-than-optimal floor space utilisation, restrictive operator movement and complex and expensive safety barriers and sensing equipment all impact a company's bottom line.

Rather than compromise either, manufacturers are turning to new technologies to achieve both safety and optimal performance objectives. DaimlerChrysler, for example, in its automotive plant in Sindelfingen, Germany has deployed innovative 3D video sensor technology that it developed in collaboration with Pilz to form a safety system that not only does away with physical barriers and light curtains, but also provides greater control of machines when safety zones are breached.

In a recent press release, DaimlerChrysler acknowledged that while it uses robotics extensively in its plants, "they lack the ability to perceive workers in their midst. As soon as they are switched on, they will continue carrying out their programmed operation until someone presses the stop button or pulls the plug. That's why robot stations must be made safe for workers by means of extensive systems. to immediately activate the emergency stop if someone crosses the barrier or unwittingly sets foot in the wrong place."

But contemporary safety systems to detect and prevent unauthorised access can be undesirable because of restrictive work patterns and excess floor space requirements. To overcome some of the limitations of such systems, DaimlerChrysler applied its vehicular 'visual assistance' technology that makes drivers aware of hazards, to safety applications, providing its image processing methods and algorithms for three-dimensional image evaluation to Pilz to adapt to industrial safety applications.

The commercial realisation of this technology is 'SafetyEye' - a 3D video sensor installed above machines that can interrupt their movement when safety zones are breached - released by Pilz at Manufacturing Week in May. The system is rated for hand, leg or body protection in accordance with Cat. 3 of EN954-1, making it suitable for most industrial applications.

Three video sensors are used to triangulate objects and zones, with image data analysed to determine the coordinates of an object in monitored areas, which are superimposed onto the monitored machine's radius of action. The algorithms search for changes in pixel values from one image to the next, triggering pre-defined responses to the detected movement.

It's a configurable system that allows users to set up specific safety zones in the region of the machine to be protected and define the resultant reaction when the zone is breached. For example, detecting a person approaching a robot a metre away, SafetyEye may slow the robot down and trigger a warning, but only stop the machine if the individual continues to approach. The machine's reaction time can be programmed into the command strings to maintain operational efficiencies while providing a high level of safety.

"Current safety technologies tend to have classic 'digital' behaviour by shutting down completely in the event of danger," states Pilz Australia MD, Frank Schrever. "However, SafetyEye is more analytical of the environment and allows the machine to respond in an intelligent fashion. For example, when a 'danger zone' is approached, it's possible to issue warnings, reduce the machine's speed and not shut it down completely unless the approach continues. Detection zones can also be activated or deactivated depending on additional external conditions, so they can be further adapted to the surrounding area."

Response time is a critical factor in maintaining a safe working environment. SafetyEye is claimed to be able to bring a robot to standstill within 150 milliseconds of the instant a person penetrates the virtual protection zone.

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