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The door holders release, allowing the doors to close automatically using door closers. [1] [2] The electric power to keep the doors open is typically 12 VDC, 24 VDC (common), 24 VAC, 120 VAC, or 240 VAC. The closed doors may or may not mechanically latch or lock in the closed position.
Door closers at this time were known as a door spring and check. Later these two devices were combined into one unit that both closed the door and slowed the speed at which this was done. These early "door closers" used a pneumatic piston to check the speed, later models used a hydraulic or oil filled device for the same effect.
An improved "shear" electromagnetic lock was patented on May 2, 1989, by Arthur, Richard and David Geringer of Security Door Controls, an access control hardware manufacturing firm. The device outlined in their designs was the same in principle as the modern magnetic lock consisting of an electromagnet and an armature plate.
In 1954, Dee Horton and Lew Hewitt invented the first sliding automatic door. The automatic door used a mat actuator. In 1960, they co-founded Horton Automatics Inc and placed the first commercial automatic sliding door on the market. [5] With the invention of the Gunn diode, microwave motion detectors became common in automatic doors in the ...
In electric power distribution, automatic circuit reclosers (ACRs) are a class of switchgear designed for use on overhead electricity distribution networks to detect and interrupt transient faults. Also known as reclosers or autoreclosers , ACRs are essentially rated circuit breakers with integrated current and voltage sensors and a protection ...
The operator is placed in the space above the sliding door. An electric motor, geared down to get a lower speed and a higher torque, drives a pulley at one end of a belt. The door is clamped to the belt. To open the door, the motor turns the pulley, which in turn turns the belt, which in turn drags the door. To close the door, the reverse occurs.