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'{{Refimprove|date=March 2008}} [[Image:Anker 01.jpg|thumb|Inline or Swiss lever escapement ''(blue)'' and balance wheel ''(yellow)'']] [[Image:Paletteankerhemmung.gif|thumb|Detail of inline lever escapement, showing the lever ''(blue)'', pallets ''(red)'', and escape wheel ''(yellow)'']] [[Image:Chinese movement escapement and jewels.jpg|thumb|A lever escapement in a mechanical watch]] The '''lever escapement''' is a type of [[escapement]] that is used in almost all [[mechanical watch]]es, as well as small mechanical non-[[pendulum]] [[clock]]s, [[alarm clock]]s, and kitchen [[timer]]s. An escapement is a mechanical linkage that gives pushes to the timepiece's [[balance wheel]], keeping it rotating back and forth, and with each swing of the balance wheel allows the timepiece's gear train to advance a fixed amount, thus moving the hands forward at a steady rate. The escapement is what makes the "ticking" sound in mechanical watches and clocks. The lever escapement was invented by British clockmaker [[Thomas Mudge (horologist)|Thomas Mudge]] around 1755,<ref name="Britten">{{cite book | last1 = Britten | first1 = Frederick James | title = Old Clocks and Watches and their Makers | publisher = B. T. Batsford | date = 1899 | location = London | pages = 349-350 | url = http://books.google.com/books?id=4e_eAAAAMAAJ&pg=PA350&lpg=PA350&dq=%22lever+escapement%22+history+massey | doi = | id = | isbn = }}</ref><ref name="Glasgow" >{{cite book | last=Glasgow | first=David | title=Watch and Clock Making | year=1885 | publisher=Cassel & Co. | location=London | pages = 180-183 | url=http://books.google.com/books?id=9wUFAAAAQAAJ&pg=PA180-183 }}</ref> and improved by [[Abraham-Louis Breguet]] (1787), [[Peter Litherland]] (1791), Edward Massey (1800), and its modern ("table roller") form was developed by George Savage in the early 1800s.<ref name="Britten" /><ref name="Glasgow" /> Since about 1900 virtually every mechanical watch, alarm clock and other portable timepiece has used the lever escapement. The advantages of the lever are, first, that it is a "detached" escapement, it allows the balance wheel to swing completely free of the escapement during most of its oscillation, except when giving it a short impulse, improving timekeeping accuracy. Second, due to "locking" and "draw" its action is very precise. Third, it is self-starting, so if the watch is jarred in use so the balance wheel stops, it will start again. A cheaper and less accurate version of the lever escapement, called the [[pin pallet escapement]], invented by [[Georges Frederic Roskopf]] in 1867, is used in clocks and timers. ==How it works== The rotation of the [[escape wheel]] is controlled by the [[pallet fork|pallets]]. The escape wheel has specially shaped teeth of either ratchet or club form, which interact with the two jewels called the entrance and exit pallets. The escape wheel, except in unusual cases, has 15 teeth and is made of steel. These pallets are attached solidly to the lever, which has at its end a fork to receive the ruby impulse pin of the balance roller which is fixed to the [[balance wheel]] shaft. The balance wheel is returned towards to its static center position by an attached balance spring (not shown in the diagram). In modern design it is common for the pallet mountings and the fork to be made as a single component. The lever is mounted on a shaft and is free to rotate between two fixed banking pins. gav suck dick == Draw == The reliability of the modern lever escapement depends upon draw; the pallets are angled so that the escape wheel must recoil a small amount during the unlocking. The draw holds the lever against the banking during the detached portion of the operating cycle. Draw angle is typically about 15 degrees to the radial. Early lever escapements lacked draw (indeed some makers considered it injurious as a cause of extra friction in unlocking); as a result a jolt could result in the escapement unlocking. == Lever watch movement == Most modern mechanical watches are [[jeweled lever]] watches, using manmade [[ruby]] or [[sapphire]] jewels for the high-wear areas of the watch. == Pin pallet escapement == {{main|Pin pallet escapement}} A cheaper, less accurate version of the lever escapement is used in [[alarm clock]]s, kitchen [[timer]]s, [[mantel clock]]s and, until the late 1970s, cheap watches, called the ''Roskopf'', ''pin-lever'', or ''[[pin-pallet escapement]]'' after [[Georges Frederic Roskopf]], who invented it in 1867. It functions similarly to the lever, except that the [[pallet lever|lever]] pallet jewels are replaced by vertical metal pins. In a lever escapement, the pallets have two angled faces, the locking face and the impulse face, which must be carefully adjusted to the correct angles. In the pin pallet escapement, these two faces are designed into the shape of the escape wheel teeth instead, eliminating complicated adjustments. The pins are located symmetrically on the lever, making beat adjustment simpler. Watches that used these escapements were called ''pin lever watches'', and have been superseded by cheap quartz watches. ==Future directions== One recent trend in escapement design is the use of new materials, many borrowed from the [[semiconductor fabrication]] industry.<ref>{{cite journal | last =Treffry | first =Timothy | title =Heart of Lightness | journal =[http://www.qpmagazine.com QP Magazine] | volume =15 | issue =24 | pages =86–91 | publisher =Skylight Creative Services, Ltd. | location =London | date =2006-05-30 | url =http://culture.hautehorlogerie.org/IMG/pdf/Num_artQP19_New_Materials-2.pdf | accessdate =2007-10-20 |format=PDF}} {{Dead link|date=October 2010|bot=H3llBot}}</ref> A problem with the lever escapement is friction. The escape wheel tooth slides along the face of the pallet, causing friction, so the pallets and teeth must be lubricated. The oil eventually thickens, causing inaccuracy, and requiring cleaning and reoiling of the movement about every 4 years. A solution is to make the escape wheel and other parts out of harder materials than steel, eliminating the need for lubrication. Materials being tried include [[silicon]], nickel phosphorus, [[diamond]], and diamond-on-silicon. [[Ulysse Nardin]] in 2001 and [[Patek Philippe]] in 2005 introduced watches with silicon escape wheels. ==See also== * [[Anchor escapement]] ==References== {{reflist}} ==External links== *''[http://www.gutenberg.org/etext/21978 An Analysis of the Lever Escapement]'', by H. R. Playtner, 1910, from [[Project Gutenberg]] [[Category:Escapements]]'