Acrank is anarm attached at a right angle to a rotating shaft by whichcircular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convertcircular motion intoreciprocating motion, or vice versa. The arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, usually called aconnecting rod (conrod).
The term often refers to a human-powered crank which is used to manually turn an axle, as in abicyclecrankset or abrace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. There is usually a bar perpendicular to the other end of the arm, often with a freely rotatable handle orpedal attached.
Familiar examples include:
Almost allreciprocating engines use cranks (withconnecting rods) to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into acrankshaft.
It was thought that evidence of the earliest true crank handle was found in a Han era glazed-earthenware tomb model of an agriculturalwinnowing fan dated no later than 200 AD,[3][4] but since then a series of similar pottery models with crank operated winnowing fans were unearthed, with one of them dating back to the Western Han dynasty (202 BC – 9 AD).[5][6] The Chinese used the crank-and-connecting rod in ancient blasting apparatus, textile machinery and agricultural machinery no later than the Western Han dynasty (202 BC – 9 AD). It was first used in the manually operated quern andlong (grain decortication item) before evolving into other devices. According to F. Lisheng and T. Qingjun, the hand-crank of the rotary quern was different from a crank, which was the combination of a hand-crank and a push-and-pull connecting rod by a hinge.[7] Eventually crank-and-connecting rods were used in the inter-conversion or rotary and reciprocating motion for other applications such as flour-sifting, treadle spinning wheels, water-powered furnace bellows, and silk-reeling machines.[8][6]
Ancient Egyptians had manual drills resembling a crank at the time of theOld Kingdom (2686–2181 BCE) and even a hieroglyph for the tool.[9] However the Ancient Egyptian drill didn't operate as a true crank.[10]
Later evidence for the crank, combined with a connecting rod in a machine, appears in the Ancient GreekHierapolis sawmill inRoman Asia from the 3rd century AD and two stonesawmills atGerasa,Roman Syria, andEphesus, Greek Ionia under Rome, (both 6th century AD).[11] On thepediment of the Hierapolis mill, awaterwheel fed by amill race is shown powering via agear train twoframe saws which cut rectangular blocks by the way of some kind of connecting rods and, through mechanical necessity, cranks. The accompanying inscription is inGreek.[12] The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train.[13][14]
The crank appears in the mid-9th century in several of the hydraulic devices described by theBanū Mūsā brothers in theirBook of Ingenious Devices.[15] These devices, however, made only partial rotations and could not transmit much power,[16] although only a small modification would have been required to convert it to acrankshaft.[17]
Al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machine in two of his water-raising machines.[18] His twin-cylinderpump incorporated a crankshaft.[19] A crank is later also described in an early 15th century Arabic manuscript ofHero of Alexandria'sMechanics.[20]
The first rotary hand mills, or rotary querns, appeared in Spain (600 BC – 500 BC),[21][22] before they spread to the East.[21][22] The handle near the outer edge of the rotary part makes the crank,[21][23][24] a human arm powering the rotation would be the connecting rod.[21] According to F. Lisheng and T. Qingjun, the hand-crank of the rotary quern was different from a crank, which was the combination of a hand-crank and a push-and-pull connecting rod by a hinge.[7]
The Antikythera mechanism, dated to around 200 BC,[25][26] used a crank as a part of its mechanism.[27] The crank was used to manually setup the starting date for a prediction.[28][29]
Later evidence for the crank, combined with a connecting rod in a machine, appears in the Ancient GreekHierapolis sawmill inRoman Asia from the 3rd century AD and two stonesawmills atGerasa,Roman Syria, andEphesus, Greek Ionia under Rome, (both 6th century AD).[11] On thepediment of the Hierapolis mill, awaterwheel fed by amill race is shown powering via agear train twoframe saws which cut rectangular blocks by the way of some kind of connecting rods and, through mechanical necessity, cranks. The accompanying inscription is inGreek.[12] The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train.[13][14]
A Roman iron crank of yet unknown purpose dating to the 2nd century AD was excavated inAugusta Raurica,Switzerland. The 82.5 cm (32 inches) long piece has fitted to one end a 15 cm (6 inches) long bronze handle, the other handle being lost.[32][31]
An true iron crank about 40 cm (16 inches) long was excavated, along with a pair of shattered mill-stones of 50 to 65 cm (20 to 26 inches) diameter and diverse iron items, inAschheim, close toMunich. The crank-operatedRoman mill is dated to the late 2nd century AD.[33] However an often cited modern reconstruction of a bucket-chain pump driven by hand-crankedflywheels from theNemi ships has been dismissed as "archaeological fantasy".[34]
In ancient literature, there is a reference to the workings of water-poweredmarble saws close toTrier, nowGermany, by the late 4th century poetAusonius;[30] about the same time, these mill types seem also to be indicated by the GreekChristian saintGregory of Nyssa fromAnatolia, demonstrating a diversified use of water-power in many parts of the Roman Empire[35] The three finds push back the date of the invention of the crank and connecting rod by a full millennium:[30]
With the crank and connecting rod system, all elements for constructing a steam engine (invented in 1712) —Hero'saeolipile (generating steam power), thecylinder andpiston (in metal force pumps), non-returnvalves (in water pumps),gearing (in water mills and clocks) — were known in Roman times.[36]
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A rotarygrindstone − the earliest representation of one −[37] which is operated by a crank handle is shown in theCarolingian manuscriptUtrecht Psalter; the pen drawing of around 830 goes back to a late antique original.[38] A musical tract ascribed to the abbotOdo of Cluny (c. 878−942) describes a fretted stringed instrument which was sounded by a resined wheel turned with a crank; the device later appears in two 12th century illuminated manuscripts.[37] There are also two pictures ofFortuna cranking her wheel of destiny from this and the following century.[37]
The use of crank handles intrepanation drills was depicted in the 1887 edition of theDictionnaire des Antiquités Grecques et Romaines and ascribed to theSpanish Muslim surgeonAbu al-Qasim al-Zahrawi; however, the existence of such a device cannot be confirmed by the original illuminations and thus has to be discounted.[20] TheBenedictine monkTheophilus Presbyter (c. 1070−1125) described crank handles "used in the turning of casting cores".[39]
The Italian physicianGuido da Vigevano (c. 1280−1349), planning for a new crusade, made illustrations for apaddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels (center of image).[40] TheLuttrell Psalter, dating to around 1340, describes a grindstone which was rotated by two cranks, one at each end of its axle; the geared hand-mill, operated either with one or two cranks, appeared later in the 15th century;[41]
Medievalcranes were occasionally powered by cranks, although more often bywindlasses.[42]
The crank became common in Europe by the early 15th century, often seen in the works of those such as theGerman military engineerKonrad Kyeser.[41] Devices depicted in Kyeser'sBellifortis include cranked windlasses (instead of spoke-wheels) for spanning siege crossbows, cranked chain of buckets for water-lifting and cranks fitted to a wheel of bells.[41] Kyeser also equipped theArchimedes screws for water-raising with a crank handle, an innovation which subsequently replaced the ancient practice of working the pipe by treading.[43] The earliest evidence for the fitting of a well-hoist with cranks is found in a miniature of c. 1425 in the GermanHausbuch of the Mendel Foundation.[44]
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The first depictions of the compound crank in the carpenter'sbrace appear between 1420 and 1430 in various northern European artwork.[45] The rapid adoption of the compound crank can be traced in the works of theAnonymous of the Hussite Wars, an unknown German engineer writing on the state of the military technology of his day: first, the connecting-rod, applied to cranks, reappeared, second, double compound cranks also began to be equipped with connecting-rods and third, the flywheel was employed for these cranks to get them over the 'dead-spot'.
One of the drawings of the Anonymous of the Hussite Wars shows a boat with a pair of paddle-wheels at each end turned by men operating compound cranks (see above). The concept was much improved by the Italian engineer and writerRoberto Valturio in 1463, who devised a boat with five sets, where the parallel cranks are all joined to a single power source by one connecting-rod, an idea also taken up by his compatriotFrancesco di Giorgio.[46]
InRenaissance Italy, the earliest evidence of a compound crank and connecting-rod is found in the sketch books ofTaccola, but the device is still mechanically misunderstood.[47] A sound grasp of the crank motion involved demonstrates a little laterPisanello who painted a piston-pump driven by a water-wheel and operated by two simple cranks and two connecting-rods.[47]
The 15th century also saw the introduction of cranked rack-and-pinion devices, called cranequins, which were fitted to thecrossbow's stock as a means of exerting even more force while spanning the missile weapon (see right).[48] In the textile industry, crankedreels for winding skeins of yarn were introduced.[41]
Around 1480, the early medieval rotary grindstone was improved with a treadle and crank mechanism. Cranks mounted on push-carts first appear in a German engraving of 1589.[49]
From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period:Agostino Ramelli'sThe Diverse and Artifactitious Machines of 1588 alone depicts eighteen examples, a number which rises in theTheatrum Machinarum Novum byGeorg Andreas Böckler to 45 different machines, one third of the total.[50]
Cranks were formerly common on some machines in the early 20th century; for example almost allphonographs before the 1930s were powered byclockwork motors wound with cranks. Reciprocating piston engines use cranks to convert the linear piston motion into rotational motion.Internal combustion engines of early 20th centuryautomobiles were usually started with hand cranks (known asstarting handles in theUK), beforeelectric starters came into general use. The last car model which incorporated a crank was theCitroën 2CV 1948-1990
The 1918Reo owner's manual describeshow to hand crank the automobile:
Acrank axle is acrankshaft which also serves the purpose of anaxle. It is used onsteam locomotives with inside cylinders.
Because of the findings at Ephesus and Gerasa the invention of the crank and connecting rod system has had to be redated from the 13th to the 6th c; now the Hierapolis relief takes it back another three centuries, which confirms that water-powered stone saw mills were indeed in use whenAusonius wrote his Mosella.
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