Thursday, November 1, 2012

HOW IT WORKS - ESCALATORS

by Dave Letink

1 Introduction
An escalator is a power-driven, continuous moving stairway designed to transport passengers up and down short, vertical distances. Areas where escalators are used a lot are shopping centers, airports and public buildings. Escalators have a lot of benefits over regular stairs: they have the capacity to move large numbers of people (using the same physical space), usually they don’t have a waiting interval and they can be used to lead people in a certain direction.

2 General information
Escalators are powered by constant speed alternating current motors and move at approximately 0,5 m/s, which is 2 km/h using about a 100 horsepower. The maximum angle lies between the 30º - 35º and the standard heights don’t reach over the 18 meters.

3 Components
The main components on an escalator are the top and bottom landing platforms, the truss, the tracks, the steps and the railing.

 3.1 The top and bottom landing platforms
At both the top as the bottom connection of the escalator a machine pit is necessary where the curved sections are located as well as the gears that drive the stairs. In the bottom doesn’t happen too much more
than this. The top, on the other hand, contains the motor assembly and the main drive gear. The pits are usually made out of concrete and are also used to anchor the ends of the escalator truss.

The landing platforms consist out of two elements: a floor plate and a comb plate. The floor plate provides a place for the passengers to stand on before they step on to the moving stairs. This plate is on the same height as the finished floor and is removable for access to the machinery below. The comb plate is the piece between the floor plate and the moving stairs which teeth fall almost seamless in the teeth of the steps so the gap will be kept to a minimum which helps prevent objects from getting caught in the it.

3.2 The truss
The truss is a hollow, metal structure which bridges the lower and upper landings of the concrete floors by making use of steel or concrete supports. The truss is the main bearing structure which carries the weight
of the escalator and the people on it.

3.3 The steps
The steps are one solid, aluminum piece made with a die-casting process. The surfaces of every step are comb-shape profiled so they will almost fit seamless in the teeth of the comb plates at the top and bottom platforms. The steps are linked by their outer wheels to a continuously metal chain so it forms a closed loop with each step still able to bend individually from its neighbors. The front and back edge of each step are connected to two wheels each: the front edge to the trailing wheels to the inner track and the back
edge to the step-wheels to the outer track. The position of the one track pertaining to the other determines the orientation of the steps (horizontal or stepwise).

3.4 The tracks
The track system is built into the truss to guide the step chain, which continuously pulls the steps from the bottom up and the other way around. Every step has 4 wheels: 2 step-wheels and 2 trailing-wheels. For
both type of wheels there’s a separate track: the step-wheel track (on the outer side) for the step wheels and the trailingwheel track (on the inner side) for the trailing wheels. The wheels on the stepwheel track are the ones that are connected to the rotating step chain and so are pulled by the main drive gear at the top of the escalator. The other set of wheels just glide along its track, following the other ones.

Because of the height difference between the front and back wheels on the tracks when the slope starts, the steps form a staircase. At the top and bottom of the escalator the two tracks come together so the front and back wheels will be in a straight line. This causes the steps to lay into a flat arrangement (not stepped
anymore), so they can travel around the curved section of the track on the top without any problems. After this they travel, hanging underneath the truss, until they reach the bottom landing. At this point the steps go into flat arrangement again and make the same curve upwards this time. At this point the tracks separate again and the steps once again will assume a stair case configuration.

3.5 The railing
The escalator railing is like a normal railing on a stair, but now the top part is moving with the escalator to give the passengers a convenient handhold. The sliding part is built up from 4 layers of material. At the
center of the railing is a ‘slider’, which is a layer of synthetic textile which allows the railing to move smoothly along its track. The next layer is the ‘tension member’, which contains steel wire that provides the handrail with the necessary strength and flexibility. The layer above this one is a chemically treated rubber that’s only there to connect his two adjacent layers. The outer layer is made of rubber and synthetic polymers. This layer is designed for mechanical wear and human vandalism.

3.6 Additional features
Some possible, additional features to escalators are motion sensors which will start and stop the escalator according to if there are people on it or not, skirt brushes which provide a better sealing between the sides of the steps and the side of the escalator and lightning, which can be put underneath the hand railing, at the
location of the skirt brushes and near the comb plates to alarm the people that they have to step of the escalator.

4 Driving system
The part that drives all the components mentioned in the chapter before, is the driving system. The driving system exists out of 3 main elements: the drive machine with gear reducer, the step drive system and the handrail drive system.

4.1 Drive machine and main drive gear
The whole system is driven by a constant speed alternating current motor that is usually located underneath the top landing platform (external drive system). The main drive gear is an enclosed, mechanical device that takes the torque, produced by the motor, and transmits it to the main drive chain. This chain moves the
steps that are connected to it by pins that fall in to their axes which are then secured by spring plugs.

4.2 Step drive system
The step drive system consists out of two chains that are directly coupled to the main drive gear which drives them around. These are the step-chain on the inside and the trailing-chain on the outside. The step chains form a loop from the main drive gears on top of the escalator to the tension carriage gear (the turn-around) at
the bottom of the escalator by the use of link pins (like on a bike chain). These chains are directly connected to the step wheels which pull the steps.

4.3 Handrail drive system
The handrail drive system is directly driven by the step drive system by adding an extra belt around the main drive gear that also drives the steps. Like this, both the steps and the handrail move at the same speed (see red arrows), making the ride for the passengers on the escalator more comfortable.

5 Conclusion
In this essay you will find the basic information of how a general escalator works. Of course there are many more escalator-systems which differ to each other when we look at them more detailed, but the basic principles will always remain the same.

 

6 Literature
Episodes from ‘How it’s made’(http://www.youtube.com/watch?v=FS-1y10W4z4&feature=related
and
http://www.youtube.com/watch?v=mV2pTMITkk)
Episode from ‘Klokhuis’
(http://tvblik.nl/het-klokhuis/roltrap)
Websites
(http://www.madehow.com/Volume-3/Escalator.html and
http://en.wikipedia.org/wiki/escalator and
http://science.howstuffworks.com/transport/enginesequipment/
escalator1.htm)
Books
(Barney, G.C., ed. Elevator
Technology. Ellis Horwood, 1986)


4 comments:

  1. Thanks for your effort :) Nice explain bro.Thanks for the share......

    ReplyDelete
    Replies
    1. wow wow wow wow mehnishh..

      Delete
  2. thanks so much for your great effort!

    ReplyDelete