Elevator Door Reopening Device: Light Curtain Multi-Beam vs Safety Edge, EN 81-20 4 J Limit and Nudging Override
Glossary ›
Door Reopening Device (Light Curtain / Safety Edge)
A safety device on the elevator car door that detects passengers or obstructions in the door opening and automatically reopens the closing door before it makes contact, preventing entrapment or crushing between the closing car and landing doors.
Full Definition
EN 81-20 requires a door reopening device (re-opening device) on all power-operated car doors. Two main types: (1) Light curtain (infrared multi-beam curtain) — an array of infrared emitter-detector pairs spanning the full height of the door opening; any interruption of any beam by a person or object triggers the door to reopen immediately; detects thin objects (as small as a finger or cane); most common modern type; detection accuracy: typically 50 mm beam spacing; (2) Safety edge (mechanical contact strip) — a rubber or pneumatic strip running the full height of the leading edge of the car door; contact with any obstruction compresses the strip and triggers door reversal; robust but detects only physical contact (not thin objects like the light curtain); older technology but still used in some retrofits. Both devices work only while the door is closing (they are deactivated once the door is fully open or the nudging sequence is triggered). EN 81-20 requirements: (a) the reopening device must be effective for at least the full height of the door opening (not just the lower zone); (b) detection zone must cover at least the full height of the door; (c) the device must automatically reopen the door when triggered and must do so before the door kinetic energy exceeds 4 J; (d) nudging overrides the reopening device after the timeout. Smoke detectors in some installations may override the reopening device during a fire alarm (fire mode).
