Lifts and Docking Systems
Webpages concerning "Lifts and Docking Systems"
|
The contents has been generating using technology developed by scientec.
Wikipedia-Article "Lifts"
- This article is about the transport device. For other meanings of the word, see elevator (disambiguation).
An elevator is a transport device used to move goods or people vertically. In British English and other Commonwealth Englishes, elevators are known more commonly as lifts, although the word elevator is familiar from American movies and television shows, just as some Americans are aware of lift from imported entertainment. Other languages may have loanwords based on either elevator (e.g. Japanese) or lift (e.g. Cantonese). Because of wheelchair access laws, elevators are often a requirement in new buildings with multiple floors.
Contents |
History
Elevators began as simple rope or chain hoists. 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" or "car") mounted on a platform within an enclosed space called a shaft or more correctly a "hoistway". In the past elevator drive mechanisms were powered by steam and water hydraulic pistons.
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 with a counterweight. The friction between the ropes and the pulley furnishes the traction which gives this type of elevator its name.
Hydraulic elevators use the principal of hydraulics to pressurize an above ground or in-ground piston to raise and lower the car. Roped Hydraulics use a combination of both ropes and hydraulic power to raise and lower cars. Recent innovations include permanent earth magnet motors, machine room-less rail mounted gearless machines, and microprocessor controls.
Which technology is 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 stories, traction elevators must be employed instead. Hydraulic elevators are usually slower than traction elevators.
In 1823, an "ascending room" made its debut in London[1].
In 1853, Elisha Otis introduced the safety elevator, which prevented the fall of the cab if the cable broke. The design of the OTIS safety is somewhat similar to one type still used today. It consists of knurled roller(s) that lock the elevator to its guides should the elevator descend at an excessive speed, which is monitored by a governor device.
On March 23, 1857 the first Otis elevator was installed at 488 Broadway in New York City. The first elevator shaft preceded the first elevator by four years. Construction for Peter Cooper's Cooper Union building in New York began in 1853. An elevator shaft was included in the design for Cooper Union, because Cooper was utterly confident a safe passenger elevator would soon be invented; the shaft however was circular because Cooper felt it was the most efficient design. Later Otis designed a special elevator for the school. Today the Otis Elevator Company, now a subsidiary of United Technologies Corporation, is the world's largest manufacturer of vertical transport systems, followed by Schindler, Thyssen-Krupp and Kone, in order.
The first electric elevator was built by Werner von Siemens in 1880. The safety and speed of electric elevators were significantly enhanced by Frank Sprague.
The development of elevators was led by the need for movement of large amounts of raw materials including coal and lumber from hillsides. The technology developed by these industries and the introduction of steel beam construction worked together to provide the need for the passenger and freight elevators we use today.
Modern elevator construction
Today, elevators are built under strict supervision of the Building Codes. Model Codes which are the standard in most US and Canadian jurisdictions require compliance with the American Society of Mechanical Engineers' standards for the installation, maintenance, and inspection of elevators. In addition other related standards are likely required to be complied with as specified by Local Authorities Having Jurisdiction.
Elevators are generally sold in prepackaged components which are inherently non-proprietary. All of the four major manufacturers sell proprietary microprocessor controls. Each manufacturer provides similar product designs, and the overriding issue for purchase is usually price and availability. In the case of renovations, the use of non-proprietary controls has become a large part of that business because it allows the owner to offer the maintenance contract to multiple bidders rather than accept a single manufacturer for the life of the elevator which can be more than 30 years. In some large campus type properties, the use of non-proprietary equipment in new construction has replaced the standard prepackaged product. Non-proprietary systems generally have a higher up front cost, but may be offset by allowing the owner to control the long term costs over the life of the elevator.
In some locations, the shaft and parts of the cab are made of transparent material for specialized "Scenic elevators." This allows riders to see outside the cab as they travel on the elevator. Some locations take advantage of this transparent material by placing the elevators along the walls of their building. This allows riders to see the outdoor environment as the cab runs along the side of the buildings.
Today, all new elevators are computer-controlled and microprocessor based. This allows the elevator system to place cabs where they are most needed in the interest of smooth running, with behavior based on analysis of building use called "Traffic Studies." Traffic Studies are done by professional elevator consultants who use specialized tools to determine the optimum size, speed and number of elevators for a building based on its peak use periods. Computer control also permits greater control of access to various floors of a building after hours and on weekends. Methods of access control include card readers, keys, and access codes entered into the control panel of the elevator.
Elevators are usually installed in a building during construction. Renovations may consist of replacements for hoistway (floor landing) doors, car doors, interior cab finishes, controls, hoist machines, hydraulic pistons and hall fixtures. At times renovations may also include replacement of the entire cab itself. In many instances the upgrading of components may require additional code compliance, these issues should be reviewed with an elevator consultant prior to the purchasing of new materials.
Elevator safety
Elevators are inherently safe. Their safety record, that of moving millions of passengers every day, without incident, is unsurpassed by any other vehicle system. Recently, however, hydraulic elevators built prior to a code change in 1972 have been found to be subject to possible catastrophic failure. The code had previously required only single-bottom hydraulic cylinders; in the event of a breach of the cylinder, an uncontrolled fall of the elevator might result. This concern is reflected in the ASME A17.1 Maintenance of Hydraulic elevators section of the 2000 edition to require verification of system integrity in underground hydraulic elevator cylinders. Because it is impossible to verify the system completely without a pressurized casing (as described below), it is necessary to actually remove the piston to inspect it. The cost of removing the piston is such that it makes no economical sense to re-install the old cylinder, and therefore it is logically necessary to install a new elevator.
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. Recent innovations called machine room-less elevators may soon make the use of hydraulic elevators obsolete.
Elevators are regulated by the Consumer Product Safety Commission and are subject to the provisions of that regulation body. In 2004 the CPSC published a consumer alert about the safe use of escalators.
Uses of elevators
Passenger service
A passenger elevator is designed to carry people and small packages.
Passenger elevator capacity
Passenger elevators capacity is related to the available floor space. Generally passenger elevators are available in typical capacities from 1,500 to 5,000 lb (680 to 2,300 kg) in 500 lb (230 kg) increments. Generally passenger elevators in buildings four stories or less are hydraulic. In buildings up to ten stories, electric elevators are likely to have speeds up to 300 ft/min (1.5 m/s), and above ten stories speeds begin at 500 ft/min (2.5 m/s) up to about 1200 ft/min (6 m/s).
Types of passenger elevators
Passenger elevators may be specialized for the service they perform, including: Hospital emergency (Code blue), front and rear entrances, double decker, and other uses. Cars may be ornate in their interior appearance, may have audio visual advertising, and may be provided with specialized recorded voice instructions. The concern for entrapping passengers requires all elevators to have communication connection to an outside 24 hour emergency service, automatic recall capability in a fire emergency, and special access for fire department use in a fire. Elevators are not an acceptable means of escape during a fire and should not be used by the public for this purpose. Signs are required in almost all US jurisdictions to "USE STAIRS IN CASE OF FIRE." Residential elevators may be small enough for one person while some are large enough for more than a dozen. Wheelchair, or platform lifts, a specialized type of elevator designed to move a wheelchair 6 ft (2 m) or less, often can accommodate just one person in a wheelchair at a time with a maximum load of 750 lb (340 kg).
Freight elevators
A freight elevator is an elevator designed to carry goods, rather than passengers. (Passengers often accompany the freight, however.) Freight elevators are exempt from some of the ASME A17.1 code requirements, as defined by the words "not for public use." Freight Elevators or Service elevators may be exempt from some of the requirements for fire service. However, new installations would likely be required to comply with these requirements. Freight elevators are generally required to display a written notice in the car that the use by passengers is prohibited, though certain freight elevators allow dual use through the use of an inconspicuous riser. Freight elevators are typically larger and capable of carrying heavier loads than a passenger elevator, generally from 5,000 to 10,000 lb (2,300 to 4,500 kg). Freight Elevators may have manually operated doors, and often have rugged interior finishes to prevent damage while loading and unloading. Although hydraulic freight elevators exist, electric elevators are more energy efficient for the work of freight lifting. A small freight elevator is often called a dumb waiter (see next section), often used for moving of small items such as dishes in a 2-story kitchen or books in a multi-story rack assembly. Passengers are never permitted on dumbwaiters. Dumbwaiters and other material lifts are required to conform to the related sections of the ASME A17.1 code in most U.S. and Canadian Jurisdictions. A specialized type of freight elevator is an Automobile Lift, used to move automobiles around a parking garage or other facility. These are material lifts by definition and are exempt from the ASME A17.1 requirements, but may have to comply with the requirements of ALI ALCTV if provided for in the local jurisdiction. Stage and Orchestra lifts are specialized lifts for use in the performing arts, and are exempt from the ASME A17.1 requirements. Local Jurisdictions may govern their use, installation and testing, however they are often left out of local code enforcement provisions due to their infrequent installation.
Dumb waiter
A small box elevator designed for the carriage of lightweight freight is called a dumb waiter (or dumbwaiter). Dumbwaiters are required to comply with ASME A17.1 in most US and Canadian Jurisdictions. Dumbwaiters are generally driven by a small electric motor with a counterweight and their capacity is limited to about 750 lb (340 kg). They may also be hand operated using a roped pulley. Dumbwaiters are used extensively in the restaurant business (hence the name) and may also be used as book lifts in libraries, or to transport mail or similar items in an office tower.
Material handling belts
A different kind of elevator is used to transport material. It generally consists of an inclined plane on which a conveyor belt runs. The conveyor often includes partitions to prevent the material from sliding backwards. These elevators are often used in industrial and agricultural applications. When such mechanisms (or spiral screws or pneumatic transport) are used to elevate grain for storage in large vertical silos, the entire structure is called a grain elevator.
Types of elevator hoist mechanisms
In general, there are three means of moving an elevator:
Traction elevators
- Geared and gearless traction elevators
Geared Traction machines are driven by AC or DC electric motors. Geared machines use worm gears to mechanically control movement of elevator cars by "rolling" steel hoist ropes over a drive sheave which is attached to a gearbox driven by a high speed motor. These machines are generally the best option for basement or overhead traction use for speeds up to 350 ft/min (1.8 m/s). Gearless Traction machines are low speed, high torque electric motors powered by AC or DC current. In this case, the drive sheave is directly attached to the end of the motor. A brake is mounted between the motor and drive sheave (or gearbox) to hold the elevator stationary at a floor. This brake is usually an external drum type and is actuated by spring force and held open electrically; a power failure will cause the brake to hold the elevator in position. In each case, cables are attached to a hitch plate on top of the cab or may be "underslung" below a cab, and then looped over the drive sheave to a counterweight attached to the opposite end of the cables which reduces the amount of power needed to move the cab. The counterweight is located in the hoistway and rides a separate rail system; as the car goes up, the counterweight goes down, and vice versa. This action is powered by the traction machine which is directed by the controller, typically a relay logic or computerized device that directs starting, acceleration, deceleration and stopping of the elevator cab. The weight of the counterweight is typically equal to the weight of the elevator cab plus 40 to 50 % of the capacity of the elevator. The grooves in the drive sheave are specially designed to prevent the cables from slipping. "Traction" is provided to the ropes by the grip of the grooves in the sheave. As the ropes age and the traction grooves wear, some traction is lost and the ropes must be replaced and the sheave repaired or replaced. Some elevators have a system called compensation. This is a separate set of cables or a chain attached to the bottom of the counterweight and the bottom of the elevator cab. This makes it easier to control the elevator because the weight will fluctuate less over the entire system. If the elevator cab is at the top of the hoistway, there is a short length of hoist cable above the car and a long length of compensating cable below the car and vice versa for the counterweight. If the compensation is cables there is an additional sheave in the pit below the elevator, to guide the cables. If the compensation is a chain, the chain is guided by a bar mounted between the counterweight rails.
Hydraulic type
- Conventional Hydraulic elevators are quite common for low and medium rise buildings (2-5 stories). They use a hydraulically powered plunger to push the elevator upwards. On some, the hydraulic piston (plunger) consists of telescoping concentric tubes, allowing a shallow tube to contain the mechanism below the lowest floor. On others, the piston requires a deeper hole below the bottom landing, usually with a PVC casing (also known as a caisson) for protection.
- Roped hydraulic.
- Twin post hydraulic
- Holeless hydraulic elevators do not require holes to be dug for the hydraulic cylinder. In one design manufactured by Otis, the cab is lifted by a pair of hydraulic jacks, one on each side of the elevator.
Climbing elevator
A climbing elevator is a self-ascending elevator with its own propulsion. The propulsion can be done by an electric or a combustion engine. Climbing elevators are used in guyed masts or towers, in order to make easy access to parts of these constructions, such as flight safety lamps for maintenance.
Paternoster
A special type of elevator is the paternoster, a constantly moving chain of boxes. A similar concept moves only a small platform, which the rider mounts while using a handhold and was once seen in multi-story industrial plants.
Controlling elevators
General controls
A typical modern passenger elevator will have:
- 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 to instruct the elevator to close immediately or remain open longer. In some elevators, holding the door open for too long will trigger an audible alarm (This alarm might confuse some people to think that the elevator is overloaded).
- A stop switch (this is not allowed under British regulations) to halt the elevator (often used to hold an elevator open while freight is loaded). Keeping an elevator stopped for too long may trigger an alarm. Often, this will be a key switch.
- An alarm button or switch, which passengers can use to signal that they have been trapped in the elevator.
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.
- A fireman's key switch, which places the elevator in a special operating mode designed to aid firefighters.
- A medical emergency key switch, which places the elevator in a special operating mode designed to aid medical personnel.
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:
- Switches to control the lights and ventilation fans in the elevator.
- An inspector's switch, which places the elevator in inspection mode (this may be situated on top of the elevator)
- An independent service switch, which selects whether the elevator's operation will be coordinated with other elevators in an elevator bank.
- Up and down buttons, to move the car up and down without selecting a specific floor. Some older elevators can only be operated this way.
Controls in early elevators
- Some older freight elevators are controlled by switches operated by pulling on adjacent ropes. Safety interlocks ensure that the inner and outer doors are closed before the elevator is allowed to move.
- Early elevators had no automatic landing positioning. Elevators were operated by elevator operators using a motor controller. The controller was contained within a cylindrical container about the size and shape of a cake container and this was operated via a projecting handle. This allowed some control over the energy supplied to the motor (located at the top of the elevator shaft or beside the bottom of the elevator shaft) 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 to get the elevator reasonably close to the landing point and then direct the outgoing and incoming passengers to "watch the step". After stopping at the landing the operator would open the door/doors. Manually operated elevators were generally refitted or the cabs replaced by automatic equipment by the 1950s.
- Large buildings with multiple elevators of this type would also have an elevator dispatcher stationed in the lobby to direct passengers and to signal the operator to leave with the use of a mechanical "cricket" noisemaker.
- Some elevators still in operation have pushbutton manual controls; an example is in a thumbnail on this page.
.
Manual pushbutton elevator controls.
Floor numbering
- Further information: Floor numbering
The elevator algorithm
The elevator algorithm, a simple algorithm by which a single elevator can decide where to stop, is summarized as follows:
- Continue travelling in the same direction while there are remaining requests in that same direction.
- If there are no further requests in that direction, then stop and become idle, or change direction if there are requests in the opposite direction.
The elevator algorithm has found an application in computer operating systems as an algorithm for scheduling hard disk requests. Modern elevators use more complex heuristic algorithms to decide which request to service next.
Computer dispatched
Efficiencies of multiple elevators installed in an office building may increase if a central dispatcher is used to group passengers going to the same floor to the same elevator. In buildings with these computer-dispatched elevator system, passengers key in their destination floor in a central dispatch panel located at the building lobby. The dispatch panel will then tell the passenger which elevator to use. Inside the elevator there is no call button to push (or the buttons are there but they cannot be pushed, they only indicate stopping floors). Manufacturers of such systems claim that average travelling time can be reduced by up to 30%. Sometimes, however, one person enters the destination for a large group of people going to the same floor. The dispatching algorithm is usually unable to completely cater for the variation, and late comers may find the elevator they're assigned to is already full.
Special operating modes
Up peak
During Up Peak mode, elevator cars in a group are recalled to the lobby to provide expeditious service to passengers arriving at the building, most typically in the morning as people arrive for work or at the conclusion of a lunch-time period. Elevators are dispatched one-by-one when they reach a pre-determined passenger load, or when they have had their doors opened for a certain period of time. The next elevator to be dispatched usually has its hall lantern or a "this car leaving next" sign illuminated to encourage passengers to make maximum use of the available elevator system capacity.
The commencement of Up Peak may be triggered by a time clock, by the departure of a certain number of fully loaded cars leaving the lobby within a given time period, or by a switch manually operated by a building attendant.
Down peak
During Down Peak mode, elevator cars in a group are sent away from the lobby towards the highest floor served, after which they commence running down the floors in response to hall calls placed by passengers wishing to leave the building. This allows the elevator system to provide maximum passenger handling capacity for people leaving the building.
The commencement of Down peak may be triggered by a time clock, by the arrival of a certain number of fully loaded cars at the lobby within a given time period, or by a switch manually operated by a building attendant.
Sabbath service
In areas with large populations of observant Jews, one may find a "Sabbath Elevator". In this mode, an elevator will stop automatically at every floor, allowing people to step on and off without having to press any buttons. Regenerative braking is also disabled if it is normally used, shunting energy collected from downward travel, and thus the gravitational potential energy of passengers, into a resistor network. This prevents violation of the Sabbath prohibition against doing useful work.
Independent service
Independent Service is a special service mode found on most elevators. It is activated by a key switch either inside the elevator itself or on a centralised control panel. When an elevator is placed on independent service, it will no longer respond to hall calls. (In a bank of elevators, traffic would be rerouted to the other elevators, while in a single elevator, the hall buttons will be disabled). The elevator will remain parked on a floor with its doors open until a floor is selected and the door close button is held until the elevator starts to travel. Independent Service is useful when transporting large goods or moving groups of people between certain floors.
Standards
The mechanical, electrical and operational design of elevators are dictated according to various standards (aka elevator codes), which may typically be international, national, state, regional or city based. Where once many standards were prescriptive, specifying exact criteria which must be complied with, there has been a shift towards more performance-based standards where the onus falls on the designer to ensure that the elevator meets or exceeds the standard.
Some of the national elevator standards include:
- USA - ASME A17
- Canada - CAN/CSA B44
- Europe - EN81
- Australia - AS1735
Because an elevator is part of a building, it must also comply with standards relating to earthquake resilience, fire standards, electrical wiring rules and so forth.
Additional requirements relating to access by disabled persons, may be mandated by laws or regulations such as the Americans with Disabilities Act