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Light beams replace interlocks with greater safety
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05/09/2003
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Problem: Many industrial machine areas are protected by interlocked doors. If there are a lot of doors, there is a significant cost and unreliability element, in that it is necessary for all the interlocks to be closed in order that machinery can operate. Malfunctioning door interlocks are often by-passed by a screw driver or piece of metal, rendering the whole system unsafe.
Solution: Erwin Sick have introduced a low cost light beam system with up to four sensor pairs, or eight individual sensors. The system can be used to protect rectangular enclosures, with sides up to 10m long with one model, or 60m long with another, to IEC 61 496 category 4, the highest possible.
The cornerstone of the L4000 system is the UE 401 safety evaluation unit. Each sensor is hard wired to the controller. As well as monitoring the sensors in rotation, so as to avoid possible cross talk, the controller also monitors connected external devices such as contactors or drives to achieve the category 4. The sensors are protected to IP67, and function over the temperature range, -20 to +55 deg C. The sensors use visible red light to ease setting up. Operating states are indicated by colour LEDs and faults are indicated on a seven segment display on the controller. Maximum response time is 30ms.
Applications: Prevention of unsafe access to machinery and robot cells, conveyor areas and between mobile racks in automated warehouses. A controller and two sensors costs about £300, a typical price for a conventional category 2 solution. TS
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Author
Tom Shelley
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