What is an elevator car door locking device?
An elevator car door locking or door restrictor is a device, attached outside of an elevator’s car door
that prevents the door to be opened from inside when the car is in transit between safe landing zones.
What is a safe landing zone?
Also referred to as the unlocking zone, the minimum safe landing zone is a vertical span of 6 inches that extends 3 inches above and 3 inches below an elevator landing. It is permissible for this span to extend up to 18 inches above or below the landing. In the layman’s term the safe landing zone is where trapped passengers can be rescued without having them to climb or jump.
Why are elevator door locking device necessary?
The usage of door locking device as a safety measure had been made mandatory for all elevators in Malaysia by Jabatan Keselamatan dan Kesihatan Pekerjaan (Department of Safety & Health) on 17th March 2011. Likewise in United State of America in their primary rule ASME A17.1, 111.5, also specified the requirement for door restrictors as below:
(a) When a car is outside the unlocking zone, the hoist way doors or car doors shall be so arranged that they cannot be opened more than 4 in. (102 mm) from inside the car.
(b) When the car doors are so arranged that they cannot be opened when the car is outside the unlocking zone, the car doors shall be open from outside the car without the use of a special tool.
(c) The doors shall be unlocked when the car within 3 in. (76 mm) above or below the landing and shall be permitted to be unlocked up to 18 in. (457 mm) above or below the landing.
For elevators installed under the 1980 edition of ASME A17.1 and later, door restrictor guidelines are provided in ASME A17.1 1998b Rule 111.5/111.12 or ASME A17.1 2000 Item 2.12.5.
The A17.1 Handbook Safety Code for Elevators and Escalators, 2000 Edition, Section 2.12.5, explains the reasoning behind the use of door restrictors in this way:
When a passenger elevator is outside the unlocking zone it is unsafe for a passenger to try to exit through the elevator entrance unassisted. In fact, there have been many reports of fatalities due to this condition. A person inside the car should not be able to accomplish their own emergency evacuation through a hoist way door when the car is located outside of the unlocking zone. This requirement may be met by restricting the opening of the car door or the hoist way door.
Industry and safety experts have agreed that during emergencies or power-loss events, the safest ways to rescue elevator passengers are inside the car until they can be rescued by professional responders.
Type of Elevator Car Door Locking Device
The first type, mechanical door restrictors are problematic because they tend to be noisy and need frequent adjustment and realignment.
The second type, electromagnetic door restrictors use photo or magnetic sensors instead of metal-to-metal contact. However, installation and calibration of the switches and levelling plates used by these devices are time-consuming but once adjusted it will last for years.
Our product is of electromagnetic type and was designed to function during power failure as it was built in with backup power supply. The system can be turned off by using toggle switch when rescuing trapped passenger at the car top. The designed is versatile and can be installed to various elevator brands; it worked independently without interrupting the original control sequence and function.
How it works?
Our product comes with three (3) major components:
a) Power and backup supply units – Provide power supply for locking device even power failure.
b) Photo sensor – To detect safe landing zone to disengage the locking device
c) Locking device – To lock the door by using electromagnetic power when out of safe landing zone.
The photo sensor will sense the car position whether the car is at the safety landing zone; if yes, the lock will be disengaged while if not the lock remains activated.