How does a Tower Crane Work

Introduction to Lift:

Humans started to use primitive lifts for moving loads vertically as early as the 4th and 3rd centuries BC. These structures were operated by human and animal power or a watermill.  Electric lifts appeared at the end of the 19th century.  The first electric lift was developed by Werner von Siemens in 1880.

Introduction of Lift

Construction of Lift:

The most popular types of lifts are roped lifts when the cabin is moved up and down by steel suspension cables.  One end of the cables is attached to the lift cabin, while the other end is connected to the counterweight through a grooved pulley, called winch.  The counterweight usually balances the weight of the cabin and half of the payload; therefore, less energy is required to operate the lift because, this way, gravity can also be utilised.  The lift cabin and the counterweight in the lift shaft move between cabin guide rails, while the drive gear, the motor and the control unit are found in the engine room above the shaft.

Construction of Lift

Operation of Lift:

The type of control system of lifts depends on the height of the building.  In the case of low-rise buildings, only a simple call button is used.  In skyscrapers, however, when calling a lift, it is possible to enter which floor the person would like to go to. 

control system of lifts

The control unit can then calculate which cabin is ideally positioned for the required journey.  The drive gear of the suspension cables is operated by an electric motor.  When the motor is turning the drive sheave in one direction, the cabin travels upwards;  when it turns in the opposite direction, the cabin travels downwards.

Safety:

At first, lifts were not very popular due to their unreliability and accident-proneness.  Mechanical malfunctions and worn out ropes caused many accidents.  That is why it was an unflavored means of transporting cargo, let alone people, inside buildings.  The emergency brake was invented in 1853 by Elisha Otis, an American inventor and industrialist.  It was presented to the public in 1854 at the World's Fair in New York.  During the demonstration, the lift was elevated to the roof of the building, where the rope was cut.  The emergency brakes prevented the lift from falling down.  Modern lifts are equipped with several safety features.  Usually, multiple cables are used to hoist the cabin, each one of which is capable of holding even the fully loaded cabin's weight.  If every suspension cable is broken and the built-in speedometer detects a speed over the safety limit, the brake system is activated automatically, fixing the lift cabin to the guide rails.

Emergency brake of Lift

Lifts are also equipped with electromagnetic brakes, which become active when stopping at a floor.  The brakes are held in an opened position by the electromagnets, this way, they automatically close in the event of a power outage.  If the cabin plummeted in spite of all these safety features, a buffer at the bottom of the shaft would cushion the impact.