elevator(redirected from dental lever)
Also found in: Dictionary, Thesaurus, Medical.
elevator,in aviation: see airplaneairplane,
heavier-than-air vehicle, mechanically driven and fitted with fixed wings that support it in flight through the dynamic action of the air.
..... Click the link for more information. .
elevator,in machinery, device for transporting people or goods from one level to another. The term is applied to the enclosed structures as well as the open platforms used to provide vertical transportation in buildings, large ships, and mines; it is also applied to devices consisting of a continuous belt or chain with attached buckets for handling bulk materials. Simple hoists were used from ancient times. From about the middle of the 19th cent., power elevators, often steam-operated, were used for conveying materials in factories, mines, and warehouses. In 1853 the American inventor Elisha G. Otis demonstrated a freight elevator equipped with a safety device to prevent falling in case a supporting cable should break. This increased public confidence in such devices and served as an impetus to the industry. Otis established a company for manufacturing elevators and patented (1861) a steam elevator. After the introduction by Sir William Armstrong of the hydraulic crane (1846), the hydraulic principle was applied to the elevator, and in the early 1870s hydraulic machines began to replace the steam-powered elevator. The hydraulic elevator is supported by a heavy piston, moving in a cylinder and operated by the water (or oil) pressure produced by pumps. As improvement of design made increased speed of movement possible, various safety devices, such as speed governors, were developed. Toward the end of the 19th cent., electric elevators came into use, and operation by electric motor gradually became the chief method. Later improved safety devices were added, and automatic and partly automatic elevators were introduced. Increase in speed of operation and improvement in general design also characterize the more modern elevators.
a stationary hoist, usually of the intermittent-operation type, for vertical motion of a car or platform along rigid guide rails mounted in a shaft.
Prototypes of elevators existed in ancient Rome as early as the first century B.C. Elevators were mentioned in sources that date to the sixth century A.D. (Egypt), the 13th century (France), and the 17th century (England and France). The first passenger elevators in Russia were built in the mid-18th century (Tsarskoe Selo and the estate of Kuskovo). In 1793 a passenger elevator with a worm drive, designed by I. P. Kulibin, was installed in the Winter Palace. Elevators with steam, hydraulic, and later electric drive appeared in the mid-19th century in connection with the development of high-rise construction (for example, in 1852 an elevator was built in the USA). The hoisting mechanisms of these elevators were winches, hydraulic cylinders with plungers, and load-carrying worm gears. In 1880, L. Siemens in Germany constructed the first electrically driven elevator with a rack-and-pinion drive mechanism. By the beginning of the 20th century, systems with an electric drive and cable traction were widely used. A distinction is made between freight elevators (general-purpose or special types, such as warehouse and sidewalk elevators) and passenger elevators (standard or high-speed; see Table 1).
|Table 1. Main technical characteristics of Soviet elevators|
|Load capacity (kg)||Rated speed (m/sec)||Height of rise (m)|
|Passenger . . .||320–1,600||0.7–4.0||45–150|
In some elevator designs the speed of travel is as high as 7 m/sec, with a load capacity of up to 260 persons—for example, in the elevator in the television tower of the Moscow television center at Ostankino.
The main requirements of elevators are safety, reliability, smoothness of acceleration, motion, and braking, and precision in stopping. Elevator operation should not cause high noise levels or interfere with television and radio reception.
A diagram of a passenger elevator is shown in Figure 1. The car is suspended on cables and moves in a shaft that passes through all floors of a building. The hoisting mechanism is a winch, mounted in the upper or lower part of the building. The
vertical position of the car is maintained by sliding or rolling shoes, which move along guide rails fastened to the walls of the shaft. For safety reasons, the car and counterweights are suspended from at least two parallel cables. Uniform tension of cables is achieved by the use of spring or balancing suspensions.
Elevator mechanisms have various functional diagrams, depending on their purpose, the height of rise, the location of winches, and the layout and construction of the building (Figure 2). The main groups of elevators are those with direct suspension of the car and counterweight, those with pulley-block suspension of the car and counterweight, and looped-cable elevators with pulley-block suspension of the car.
Safe operation of elevators is ensured by such devices as car catchers and speed limiters, which stop the car if the normal speed is exceeded by 15 percent or more or if a cable breaks or is weakened. Wedge-type catchers are a widely used design. Upon operation of the actuating mechanism the wedges are raised and press against the guide rails; if the car descends still further, self-tightening of wedges occurs and the car is stopped. The catcher is connected to a speed limiter, whose centrifugal locking device brakes the sheave and the cable as soon as the car reaches the speed limit. Upon subsequent motion of the car, the catchers are actuated by a system of rods.
The main type of drive for elevators in large-scale use is the AC electric type. The most common system has a two-speed asynchronous electric motor with a cage rotor, which makes possible a significant reduction in speed and ensures precise stopping of the car. Miniature drives are used for precise stopping of freight elevators with a single guide rail. Special AC or DC electric drives are used for elevators with speeds exceeding 1 m/sec; such drives have a wide range of speed control, with constant acceleration.
The control of an electric elevator drive (start, acceleration, deceleration, stop, and change in the direction of motion) is provided by starting and control apparatus. Safety of operation is provided by automatic electric and mechanical protective and interlocking devices. If necessary, elevators may be equipped with automatic doors, optical signals, and two-way communication between the car and the starter’s desk, which serves several elevators simultaneously. The regulation of an elevator may be internal (from within the car), external (from the loading area), or mixed, depending on the location of the control apparatus. Collective control, which makes possible registration of commands from the cars, as well as calls from individual floors and their subsequent answer following the floor sequence during an up or down trip of the cabin, is often used.
In high-rise buildings the efficiency of use of an elevator is increased if passengers are first brought to a given level on nonstop high-speed elevators and then to higher floors by an ordinary elevator.
Public and administrative buildings with large passenger traffic are equipped with dual or group elevator control systems (for three to six elevators). Such systems are intended for organizing automatic, combined operation of elevators to achieve maximum throughput and minimum waiting time. Operating schedules for morning, day, and evening may be set by the starter or programmed automatically as a function of the intensity and direction of traffic.
Standard designs of normal and high-speed passenger and freight elevators are used for serving blast furnaces, petroleum refineries, and television towers. The main parameters of the elevators and the dimensions of cars, shafts, machine rooms, and winch rooms are regulated by GOST (the All-Union State Standard), data from which are used to coordinate the mechanical and structural parts of the installations and to develop series of standardized passenger and freight elevators that are suitable for any building structure.
REFERENCESPavlov, N. G. Lifty i pod”emniki. Moscow-Leningrad, 1965.
Brodskii, M. G., I. M. Vishnevetskii, and Iu. V. Greiman. Remont, modernizatsiia i ekspluatatsiia liftov, 2nd ed. Moscow, 1968.
Elektrooborudovanie liftov: Katalog-spravochnik, issues 1–2. Moscow, 1968–69.
Montazh i ekspluatatsiia liftov. Moscow, 1969.
E. M. STARIKOV
(Russian, elevator), a continuous-operation machine used to transport loads vertically or on an incline.
Bucket, tray, and cradle-type elevators are distinguished. Bucket elevators are designed to lift pulverized, granular, or lumpy bulk materials vertically or at angles greater than 60°. Tray elevators and cradle-type elevators are used for lifting unit loads such as parts, bags, and boxes and may be loaded and unloaded intermittently. Bucket elevators are employed in metallurgy, machine
building, and chemical and food production, as well as at ore-enrichment plants and granaries. Tray elevators and cradle-type elevators are used at enterprises of various branches of industry, at supply depots, and in stores. They are also found in warehouses in the form of mobile shelving on which products are stored and made available.
A bucket elevator (Figure 1) consists of an endless belt that passes around drive and tension pulleys (or sprockets) and on which buckets are mounted. The supporting and enclosing structure of the elevator may be a welded steel casing with a loading spout and a discharge spout. The elevator’s drive comprises an electric motor, a reducing gear, clutches, and a backstop that prevents reversal of the belt. A screw takeup or a gravity takeup may be used in the elevator.
The belt of a low-speed bucket elevator runs at speeds of up to 1 m/sec, whereas that of a high-speed elevator runs at up to 4 m/-sec. Capacities of bucket elevators range from 5 m3/hr to 500 m3/hr, and the height of lift H rarely exceeds 60 m. The basic parameters of such elevators (see Figure 1) include the bucket’s width Bb, height h, overhang A, and effective capacity (as measured to the rim of the front wall); also included is the spacing ab between buckets. High-speed elevators have alternating deep and shallow buckets that are spaced in such a way that ab = (2.5–3)h; the buckets are mounted on a rubberized conveyor belt or on a short-link chain. Slow-speed elevators use closely spaced (ab = h), acute-angled buckets with rounded bottoms. The buckets have side guides and are attached between two chains.
A tray elevator (Figure 2,a) has two vertical pintle chains that are equipped with bushings and that turn around a drive sprocket at the head terminal and a tension sprocket at the foot terminal. Fork trays that conform to the size and shape of the load are rigidly attached to the chains. The trays are loaded either automatically from a table with baffles or manually and are unloaded when they are tipped at the upper end of the descending run. The chains operate at a speed of 0.2–0.3 m/sec.
A cradle-type elevator (Figure 2,b) differs from a tray elevator in the method by which the transporting unit is attached. Pivot-ally mounted, the cradle remains horizontal throughout the entire run. The cradles are loaded during the ascending run and unloaded during the descending run. Cradle-type elevators operate at speeds of 0.2–0.3 m/sec.
REFERENCESSpivakovskii, A. O., and V. K. D’iachkov. Transportiruiushchie mashiny, 2nd ed. Moscow, 1968.
Mashiny nepreryvnogo transporta. Edited by V. I. Plavinskii. Moscow, 1969.
What does it mean when you dream about an elevator?
Because they travel up and down in space, elevators participate in the larger meaning of height and depth. Thus, an ascending elevator in a dream can mean almost anything from rising in status to rising in awareness, whereas one descending may mean lowered status or submerging into the depths of the unconscious. In and of themselves, elevators are often regarded as threatening, because on elevators we are often forced into close quarters with strangers and because they sometimes plummet down the elevator shaft, killing the passengers.