Crank (mechanism)
From Wikipedia, the free encyclopedia
A crank is an arm at right angles to a shaft (an axle or spindle), by which motion is imparted to or received from the shaft; it is also used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm keyed to it.
One application is human-powered turning of the axle. Often there is a bar perpendicular to the other end of the arm, often with a freely rotatable handle on it to hold in the hand, or in the case of operation by a foot (usually with a second arm for the other foot), with a freely rotatable pedal.
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[edit] Examples
Familiar examples include:
[edit] Using a hand
- mechanical pencil sharpener
- fishing reel and other reels for cables, wires, ropes, etc.
- manually operated car window
- the crank set that drives a trikke through its handles.
[edit] Using the feet
- the crankset that drives a bicycle via the pedals.
- treadle sewing machine
[edit] Engines
Almost all reciprocating engines use cranks to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft.
[edit] History
The eccentrically mounted handle of the rotary handmill which originated in 5th century BC Spain and ultimately spread all over the Roman Empire constitutes a crank.[1][2] An iron crank handle has been excavated in Augst, Germany. The 82.5 cm long piece with a 15 cm long handle is of yet unknown purpose and dates to no later than ca. 250 AD.[3]
The earliest evidence for the crank as part of a machine, that is in combination with a connecting rod, appears in late Roman water-powered saw mills dating from the late 3rd (at Hierapolis) to 6th century AD (at Ephesus respectively Gerasa).[4]
In China, hand-operated cranks appeared during the Han Dynasty (202 BC-220 AD), as Han era glazed-earthenware tomb models portray, and was used thereafter in China for silk-reeling and hemp-spinning, for the agricultural winnowing fan, in the water-powered flour-sifter, for hydraulic-powered metallurgic bellows, and in the well windlass.[5]
The crank appears again in the early 9th century in several of the hydraulic devices described by the Banū Mūsā brothers in their Book of Ingenious Devices. A device shown in the 9th century Carolingian manuscript Utrecht Psalter is a crank handle used with a rotary grindstone.[6] Scholars point to the use of crank handles in trepanation drills in a 10th century work by the Spanish Muslim surgeon Abu al-Qasim al-Zahrawi (936–1013).[6] The Benedictine monk Theophilus Presbyter (c. 1070–c.1125) described crank handles "used in the turning of casting cores" according to Needham.[7]
Al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machin in two of his water-raising machines.[8] The Italian physican and inventor Guido da Vigevano (c. 1280–1349) made illustrations for a paddle boat and a war carriages that were propelled by manually turned crankshafts and gear wheels.[9] The crank became common in Europe by the early 15th century, seen in the works of those such as the military engineer Konrad Kyeser (1366–after 1405).[9]
Cranks were formerly common on some machines in the early 20th century; for example almost all phonographs before the 1930s were powered by clockwork motors wound with cranks, and internal combustion engines of automobiles were usually started with cranks (known as starting handles [10] in the UK), before electric starters came into general use.
[edit] Footnotes
- ^ a b Ritti, Grewe & Kessener 2007, p. 159
- ^ a b Lucas 2005, p. 5, fn. 9
- ^ Laur-Belart 1988, p. 51–52, 56, fig. 42
- ^ Ritti, Grewe & Kessener 2007, p. 161
- ^ Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Part 2, Mechanical Engineering. Taipei: Caves Books, Ltd. Pages 118–119.
- ^ a b Needham, Volume 4, Part 2, 112.
- ^ Needham, Volume 4, Part 2, 112–113.
- ^ Ahmad Y Hassan. The Crank-Connecting Rod System in a Continuously Rotating Machine.
- ^ a b Needham, Volume 4, Part 2, 113.
- ^ Last car with a starting handle: Motoring Discussion forum
[edit] References
- Laur-Belart, Rudolf (1988), Führer durch Augusta Raurica (5th ed.), Augst
- Lucas, Adam Robert (2005), "Industrial Milling in the Ancient and Medieval Worlds. A Survey of the Evidence for an Industrial Revolution in Medieval Europe", Technology and Culture 46: 1-30
- Ritti, Tullia; Grewe, Klaus; Kessener, Paul (2007), "A Relief of a Water-powered Stone Saw Mill on a Sarcophagus at Hierapolis and its Implications", Journal of Roman Archaeology 20: 138–163
[edit] See also
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[edit] External links and books
- Crank highlight: Hypervideo of construction and operation of a four cylinder internal combustion engine courtesy of Ford Motor Company
- Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books, Ltd.
- Kinematic Models for Design Digital Library (KMODDL) - Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library of classic texts on mechanical design and engineering.
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