Machine Vision Keeps An Eye on Workers

A machine vision system from Pilz, the company's first, handles safety monitoring tasks

Joseph Ogando, Senior Editor -- Design News, August 27, 2008

Optical devices such as light curtains have long been a mainstay of machine safety systems, but Pilz has rolled out its first true machine-vision safety product.

Called SafetyEye, the system uses a small-aperture 3-D camera to perform body detection tasks around production machines and robot cells. According to Eric Hollister, SafetyEye's product engineer, the system mounts above the equipment it monitors and can cover some large three-dimensional spaces. Mounted at about 7.5m, for example, it covers an area of roughly 75 sq m. Should a worker or other object stray into SafetyEye's detection zone, the system can trip a machine or robot shut-down. The system also allows the creation of a "warning zone," in which intrusions would trigger only a slow-down of machine processes.

It's tempting to make a direct comparison between SafetyEye and existing optical safety components like light curtains or laser-based systems. Yet a safety system based on true machine vision does differ in terms of how it is specified and in the kind of design and cost advantages it offers.

In terms of the specs, SafetyEye has a reaction time in the neighborhood of 300 ms, which is slower than many laser-based systems. Yet Hollister points out that 2-D, horizontal laser systems need to factor in a "depth-penetration" that essentially requires them to broaden their detection zone beyond what their reaction time alone would dictate. "In a 2-D system, you have to account for the fact that people can lean into the detection zone," Hollister says. With a 3-D system, however, that depth penetration factor can be eliminated. "In the end, that equals out SafetyEye's additional reaction time," he says.

As for design advantages, one SafetyEye above a machine or robot cell promises to take the place of multiple safety devices and physical guarding elements. For example, a typical rotary table for robot cell loading might have two light curtains, one vertical and one horizontal. "One SafetyEye could monitor that entire robot cell," Hollister says.

And fewer devices can have big implications in simplifying the design of safety systems. "Think of all the wiring and development work you save when you start eliminating light curtains and electronic gates," Hollister says. And when production lines change over time, which they often do, there's no need to relocate and rewire the safety systems.  "You just reprogram the SafetyEye to accommodate the line changes," he says.

Even though the SafetyEye hardware alone does have an initial price 4 or 5 times greater than, say, a low-cost light curtain, the installation flexibility and wiring reduction more than make up for any price premium, Hollister argues.

Pilz is not pushing SafetyEye for all applications. Light curtains are still most appropriate for hand-based operations, such as press guarding. "SafetyEye is really just intended for body detection," Hollister says.

SafetyEye debuted in Germany earlier this year and has just launched in North America, where Hollister says it is currently being commissioned in its first two robotic safety applications.