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Light curtains detect direction of travel without sensors

01 December, 2015

The Austrian automation specialist B&R has joined forces with the Italian sensor-maker Datalogic to develop a safety light curtain that can sense the direction in which an object is travelling, and determine its height and length, without needing the position sensors that have traditionally been used for muting and blanking applications.

This results in savings in time and money when installing the SG4 Fieldbus light curtains. More time is saved by avoiding the need to set DIP switches, or to configure software when setting up the curtains. And, instead of operators having to interpret blinking LED patterns, the curtains show error messages on a plain-text display.

The key to the technology is the openSafety light grid profile developed by the Ethernet Powerlink Standardisation Group (EPSG). This replaces the hardwiring that has previously been needed for light grids. The curtain connects directly to the real-time, Ethernet-based Powerlink network.

By mounting a light curtain at an angle, the profile can be used to monitor individual beams in the grid to determine which are broken in what order, and to inform a connected SafeLogic controller. Based on which beam is broken first, it is possible to determine the direction that an object is passing through the grid, without needing any extra hardware. It is also possible to gauge the object’s height and, using the transport speed, its length as well.

Using this information, the safety controller can confirm that a product moving through the light curtain is the one that was expected.

If a person sits on a product to bypass the photoelectric sensors, the machine will enter a safe state. “Solutions using conventional light grids require a lot of technical effort in order to detect that type of tampering,” suggests Miodrag Veselic, B&R’s openSafety technology manager.

“B&R is the first manufacturer to work on completely integrating this type of profile into its automation landscape,” he adds. Since no safe I/O channels are necessary, an application with openSafety light grids is less expensive than a hardwired solution.” 

Safety functions such as muting and blanking are programmed in B&R’s Automation Studio software. Once a light curtain has been installed and a node number has been set on the device, the rest of the configuration is handled in the software. 

A novel angle on light curtains: the Datalogic/B&R system can detect which direction an object is moving without needing position sensors

“When this type of light grid is mounted at an angle, we are able to obtain all the data we need for intelligent muting,” says Veselic.

“The troubleshooting possibilities of the intelligent light grid are a huge step forward as well,” he adds. Error messages that used to require painstakingly reading and interpreting of LED blink patterns, can now be viewed in plain text. This provides more detailed diagnostics and cuts downtime.

Veselic points out that especially significant time savings are possible with the new light curtain when they are used in machines being produced in series. “This is because, once written, the safety application can be re-used on every machine,” he explains. “The light grid simply has to be connected to the network. The safety controller automatically detects whether it is dealing with the correct light grid model and transfers the configuration to the device. Errors that might otherwise result from manual configuration or on-site wiring are prevented.” 

The new system also avoids potential errors when trying to set (or reset) awkward-to-reach DIP switches, especially after a light curtain has been installed.

According to Datalogic’s safety product manager, Paolo Zanetta, the new light curtains will “allow us to offer … a whole new realm of safety solutions. The customer enjoys maximum conceptual design freedom, and even saves money compared to applications with simple binary data structures.”

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