Crank (mechanism)

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.

Examples

Familiar examples include:

Using a hand

• mechanical pencil sharpener
• fishing reel and other reels for cables, wires, ropes, etc.
• train window
• manually operated car window
• the crank set that drives a trikke through its handles.

Using feet

• the crankset that drives a bicycle via the pedals.
• treadle sewing machine

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.

History

The earliest hand-operated cranks appeared in China 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. Some scholars believe that a device shown in the 9th century Carolingian manuscript Utrecht Psalter is a crank handle used with a rotary grindstone. 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). The Benedictine monk Theophilus Presbyter (c. 1070–c.1125) described crank handles "used in the turning of casting cores" according to Needham. It was through Al-Jazari (1136–1206) that the use of crank became widely established in the Middle East, as he was the first to incorporate a crankshaft in a machine. The connecting rod was also invented by Al-Jazari, and was used in a crank and connecting rod system in a rotating machine he developed in 1206, in two of his water-raising machines. The Italian physican and inventor Guido da Vigevano (c. 1280–1349) made illustrations for a paddle boat and a Skizze Kurbelwagen (Vigevano).jpeg that were propelled by manually turned crankshafts and gear wheels. 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).

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 in the UK), before electric starters came into general use.

References

See also

• Winch
• Piston motion equations
• Nothing grinder
• Sun and planet gear

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.