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FARAZ SOUD ALMAS ELEVATOR
An elevator (US and Canada) or lift (UK, Ireland and Australia) is a type of vertical transportation device that moves people or goods between floors (levels, decks) of a building, vessel, or other structure. Elevators are typically powered by electric motors that drive traction cables and counterweight systems like a hoist, although some pump hydraulic fluid to raise a cylindrical piston like a jack.
In agriculture and manufacturing, an elevator is any type of conveyor device used to lift materials in a continuous stream into bins or silos. Several types exist, such as the chain and bucket elevator, grain auger screw conveyor using the principle of Archimedes' screw, or the chain and paddles or forks of hay elevators. Languages other than English may have loanwords based on either elevator or lift. Because of wheelchair access laws, elevators are often a legal requirement in new multistory buildings, especially where wheelchair ramps would be impractical.
Design:
Some people argue that elevators began as simple rope or chain hoists (see Traction elevators below). An elevator is essentially a platform that is either pulled or pushed up by a mechanical means. A modern-day elevator consists of a cab (also called a "cage", "carriage" or "car") mounted on a platform within an enclosed space called a shaft or sometimes a "hoistway". In the past, elevator drive mechanisms were powered by steam and water hydraulic pistons or by hand. In a "traction" elevator, cars are pulled up by means of rolling steel ropes over a deeply grooved pulley, commonly called a sheave in the industry. The weight of the car is balanced by a counterweight. Sometimes two elevators are built so that their cars always move synchronously in opposite directions, and are each other's counterweight. The friction between the ropes and the pulley furnishes the traction which gives this type of elevator its name.
Hydraulic elevators use the principles of hydraulics (in the sense of hydraulic power) to pressurise an above ground or in-ground piston to raise and lower the car (see Hydraulic elevators below). Roped hydraulics use a combination of both ropes and hydraulic power to raise and lower cars. Recent innovations include permanent magnet motors, machine room-less rail mounted gearless machines, and microprocessor controls. The technology used in new installations depends on a variety of factors. Hydraulic elevators are cheaper, but installing cylinders greater than a certain length becomes impractical for very-high lift hoistways. For buildings of much over seven floors, traction elevators must be employed instead. Hydraulic elevators are usually slower than traction elevators.
Elevators are a candidate for mass customisation. There are economies to be made from mass production of the components, but each building comes with its own requirements like different number of floors, dimensions of the well and usage patterns.
Doors
Elevator doors prevent riders from falling into, entering, or tampering with anything in the shaft. The most common configuration is to have two panels that meet in the middle, and slide open laterally. In a cascading telescopic configuration (potentially allowing wider entryways within limited space), the doors roll on independent tracks so that while open, they are tucked behind one another, and while closed, they form cascading layers on one side. This can be configured so that two sets of such cascading doors operate like the center opening doors described above, allowing for a very wide elevator cab. In less expensive installations the elevator can also use one large "slab" door: a single panel door the width of the doorway that opens to the left or right laterally. Some buildings have elevators with the single door on the shaftway, and double cascading doors on the cab.
Machine room-less (MRL) elevators
Machine room-less elevators are designed so that most of the components fit within the shaft containing the elevator car; and a small cabinet houses the elevator controller. Other than the machinery being in the hoistway, the equipment is similar to a normal traction or hole-less hydraulic elevator. The world's first machine room-less elevator, the Kone MonoSpace was introduced in 1996, by Kone. The benefits are:
- creates more usable space
- use less energy (70–80% less than standard hydraulic elevators)
- uses no oil (assuming it is a traction elevator)
- all components are above ground similar to roped hydraulic type elevators (this takes away the environmental concern that was created by the hydraulic cylinder on direct hydraulic type elevators being stored underground)
- slightly lower cost than other elevators; significantly so for the hydraulic MRL elevator
- can operate at faster speeds than hydraulics but not normal traction units.
Hydraulic elevators
- Conventional hydraulic elevators. They use an underground hydraulic cylinder, are quite common for low level buildings with two to five floors (sometimes but seldom up to six to eight floors), and have speeds of up to 1 m/s (200 ft/min). For higher rise applications, a telescopic hydraulic cylinder can be used.[citation needed]
- Holeless hydraulic elevatorswere developed in the 1970s, and use a pair of above ground cylinders, which makes it practical for environmentally or cost sensitive buildings with two, three, or four floors.
- Roped hydraulic elevatorsuse both above ground cylinders and a rope system, allowing the elevator to travel further than the piston has to move.
The low mechanical complexity of hydraulic elevators in comparison to traction elevators makes them ideal for low rise, low traffic installations. They are less energy efficient as the pump works against gravity to push the car and its passengers upwards; this energy is lost when the car descends on its own weight. The high current draw of the pump when starting up also places higher demands on a building's electrical system. There are also environmental concerns should the lifting cylinder leak fluid into the ground.[35]
The modern generation of low-cost, machine room-less traction elevators made possible by advances in miniaturisation of the traction motor and control systems challenges the supremacy of the hydraulic elevator in their traditional market niche
Pit of a hydraulic scenic elevator with metal grating on bottom. This elevator travels 7 stories.
Controlling elevators
Manual controls
In the first half of the twentieth century, almost all elevators had no automatic positioning of the floor on which the cab would stop. Some of the older freight elevators were controlled by switches operated by pulling on adjacent ropes. In general, most elevators before WWII were manually controlled by elevator operators using a rheostat connected to the motor. This rheostat (see picture) was enclosed within a cylindrical container about the size and shape of a cake. This was mounted upright or sideways on the cab wall and operated via a projecting handle, which was able to slide around the top half of the cylinder.
The elevator motor was located at the top of the shaft or beside the bottom of the shaft. Pushing the handle forward would cause the cab to rise; backwards would make it sink. The harder the pressure, the faster the elevator would move. The handle also served as a dead man switch: if the operator let go of the handle, it would return to its upright position, causing the elevator cab to stop. In time, safety interlocks would ensure that the inner and outer doors were closed before the elevator was allowed to move.
This lever would allow some control over the energy supplied to the motor and so enabled the elevator to be accurately positioned — if the operator was sufficiently skilled. More typically, the operator would have to "jog" the control, moving the cab in small increments until the elevator was reasonably close to the landing point. Then the operator would direct the outgoing and incoming passengers to "watch the step".
Manual pushbutton elevator controls
Automatic elevators began to appear as early as the 1920s,[citation needed] their development being hastened by striking elevator operators which brought large cities dependent on skyscrapers (and therefore their elevators) such as New York and Chicago to their knees. Self service elevators were not allowed in New York City until 1922. Prior to this, non-luxury buildings that could not afford an attendant were built as five-story walk ups. These electromechanical systems used relay logic circuits of increasing complexity to control the speed, position and door operation of an elevator or bank of elevators.
The Otis Autotronic system of the early 1950s brought the earliest predictive systems which could anticipate traffic patterns within a building to deploy elevator movement in the most efficient manner. Relay-controlled elevator systems remained common until the 1980s and their gradual replacement with solid-state, microprocessor-based controls are now the industry standard. Most older, manually-operated elevators have been retrofitted with automatic or semi-automatic controls.
General controls
A typical modern passenger elevator will have
- Outside the elevator, buttons to go up or down (the bottom floor only has the up button, the top floor only has the down button, and every floor in between has both)
- Space to stand in, guardrails, seating cushion (luxury)
- Overload sensor – prevents the elevator from moving until excess load has been removed. It may trigger a voice prompt or buzzer alarm. This may also trigger a "full car" indicator, indicating the car's inability to accept more passengers until some are unloaded.
- Electric fans or air conditioning units to enhance circulation and comfort.
- A control panel with various buttons. In many countries, button text and icons are raised to allow blind users to operate the elevator; many have Braille text besides. Buttons include:
- Call buttons to choose a floor. Some of these may be key switches (to control access). In some elevators, certain floors are inaccessible unless one swipes a security card or enters a passcode (or both).
- Door open and door close buttons.
The operation of the door open button is transparent, immediately opening and holding the door, typically until a timeout occurs and the door closes. The operation of the door close button is less transparent, and it often appears to do nothing, leading to frequent but incorrect[39] reports that the door close button is a placebo button: either not wired up at all, or inactive in normal service.[40][41][42][43] Working door open and door close buttons are required by code in many jurisdictions, including the United States, specifically for emergency operation: in independent mode, the door open and door close buttons are used to manually open or close the door.[39][44] Beyond this, programming varies significantly, with some door close buttons immediately closing the door, but in other cases being
delayed by an overall timeout, so the door cannot be closed until a few seconds after opening. In this case (hastening normal closure), the door close button has no effect. However, the door close button will cause a hall call to be ignored (so the door won't reopen), and once the timeout has expired, the door close will immediately close the door, for example to cancel a door open push. The minimum timeout for automatic door closing in the US is 5 seconds,[45] which is a noticeable delay if not over-ridden.
- An alarm button or switch, which passengers can use to warn the premises manager that they have been trapped in the elevator.
- A set of doors kept locked on each floor to prevent unintentional access into the elevator shaft by the unsuspecting individual. The door is unlocked and opened by a machine sitting on the roof of the car, which also drives the doors that travel with the car. Door controls are provided to close immediately or reopen the doors, although the button to close them immediately is often disabled during normal operations, especially on more recent elevators. Objects in the path of the moving doors will either be detected by sensors or physically activate a switch that reopens the doors. Otherwise, the doors will close after a preset time. Some elevators are configured to remain open at the floor until they are required to move again. Regulations often require doors to close after use to prevent smoke from entering the elevator shaft in event of fire.
- Elevators in high traffic buildings often have a "nudge" function (the Otis Autotronicsystem first introduced this feature) which will close the doors at a reduced speed, and sound a buzzer if the "door open" button is being deliberately held down, or if the door sensors have been blocked for too long a time.
- A stop switch (not allowed under British regulations[citation needed]) to halt the elevator while in motion and often used to hold an elevator open while freight is loaded. Keeping an elevator stopped for too long may set off an alarm. Unless local codes require otherwise, this will most likely be a key switch.
Some elevators may have one or more of the following
- An elevator telephone, which can be used (in addition to the alarm) by a trapped passenger to call for help. This may consist of a transceiver, or simply a button. This feature is often required by local regulations.
- Hold button: This button delays the door closing timer, useful for loading freight and hospital beds.
- Call cancellation: A destination floor may be deselected by double clicking.
- Access restriction by key switches, RFID reader, code keypad, hotel room card, etc.
One or more additional sets of doors. This is primarily used to serve different floor plans: on each floor only one set of doors opens. For example, in an elevated crosswalk setup, the front doors may open on the street level, and the rear doors open on the crosswalk level. This is also common in garages, rail stations, and airports. Alternatively, both doors may open on a given floor. This is sometimes timed so that one side opens first for getting off, and then the other side opens for getting on, to improve boarding/exiting speed. This is particularly useful when passengers have luggage or carts, as at an airport, due to reduced manoeuvrability.
Dual door open and door close buttons, in an elevator with two sets of doors.
In case of dual doors, there may be two sets of door open and door close buttons, with one pair controlling the front doors, from the perspective of the console, typically denoted <> and ><, with the other pair controlling the rear doors, typically denoted with a line in the middle, <|> and >|<, or double lines, |<>| and >||<. This second set is required in the US if both doors can be opened at the same landing, so that the doors can both be controlled in independent service.[39][46]
- Security camera
- Plain walls or mirrored walls.
- Glass windowpane providing a view of the building interior or onto the streets.
'S' "Signal" button, found in US elevators of 1991–2012 vintage.
An audible signal button, labelled "S": in the US, for elevators installed between 1991 and 2012 (initial passage of ADA and coming into force of 2010 revision), a button which if pushed, sounds an audible signal as each floor is passed, to assist visually impaired passengers. No longer used on new elevators, where the sound is obligatory.[47]
Other controls, which are generally inaccessible to the public (either because they are key switches, or because they are kept behind a locked panel), include:
- Fireman's service, phase II key switch
- Switch to enable or disable the elevator.
- An inspector'sswitch, which places the elevator in inspection mode (this may be situated on top of the elevator)
- Manual up/down controls for elevator technicians, to be used in inspection mode, for example.
- An independent service/exclusive mode(also known as "Car Preference"), which will prevent the car from answering to hall calls and only arrive at floors selected via the panel. The door should stay open while parked on a floor. This mode may be used for temporarily transporting goods.
- Attendant service mode
- Large buildings with multiple elevators of this type also had an elevator dispatcherstationed in the lobby to direct passengers and to signal the operator to leave with the use of a mechanical "cricket" noisemaker.
Past problems with hydraulic elevators include underground electrolytic destruction of the cylinder and bulkhead, pipe failures, and control failures. Single bulkhead cylinders, typically built prior to a 1972 ASME A17.1 Elevator Safety Code change requiring a second dished bulkhead, were
subject to possible catastrophic failure. The code previously permitted only single-bottom hydraulic cylinders. In the event of a cylinder breach, the fluid loss results in uncontrolled down movement of the elevator. This creates two significant hazards: being subject to an impact at the bottom when the elevator stops suddenly and being in the entrance for a potential shear if the rider is partly in the elevator. Because it is impossible to verify the system at all times, the code requires periodic testing of the pressure capability. Another solution to protect against a cylinder blowout is to install a plunger gripping device. Two commercially available are known by the marketing names "LifeJacket" and "HydroBrake". The plunger gripper is a device which, in the event of an uncontrolled downward acceleration, nondestructively grips the plunger and stops the car. A device known as an overspeed or rupture valve is attached to the hydraulic inlet/outlet of the cylinder and is adjusted for a maximum flow rate. If a pipe or hose were to break (rupture), the flow rate of the rupture valve will surpass a set limit and mechanically stop the outlet flow of hydraulic fluid, thus stopping the plunger and the car in the down direction.
In addition to the safety concerns for older hydraulic elevators, there is risk of leaking hydraulic oil into the aquifer and causing potential environmental contamination. This has led to the introduction of PVC liners (casings) around hydraulic cylinders which can be monitored for integrity.
In the past decade, recent innovations in inverted hydraulic jacks have eliminated the costly process of drilling the ground to install a borehole jack. This also eliminates the threat of corrosion to the system and increases safety.
Faraz Soud Almas elevator