Automatic watch

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The underside view of a Gruen automatic watch with a transparent case back, showing its ETA 2824-2 movement. The semicircular rotor which winds the mainspring is plainly visible

An automatic or self-winding watch is a mechanical wrist watch in which the mainspring is wound automatically as a result of natural motion of the wearer's arm, to provide energy to run the watch, making manual winding unnecessary. A mechanical watch which is neither self-winding nor electrically driven may be called a manual watch. Many of the mechanical watches sold today are self-winding. Others require manual winding on a daily or weekly basis; still others use mechanical or solar energy to charge a battery driving a quartz movement.

How it works

A mechanical watch is powered by an internal spiral mainspring which turns the gears that move the hands. The spring loses energy as the watch runs, so in a manual watch movement the spring must be wound by turning a small knob on the case to provide energy to run the watch otherwise, once the watch loses its stored energy, it stops.

A self-winding watch movement has a mechanism which winds the mainspring.^[1] The watch contains an eccentric weight (the rotor), which turns on a pivot. The normal movements of the user's arm cause the rotor to pivot on its staff, which is attached to a ratcheted winding mechanism. The motion of the wearer's arm is thereby translated into circular motion of the rotor which, through a series of reverser and reducing gears, eventually winds the mainspring. Modern self-winding mechanisms have two ratchets and wind the mainspring during clockwise and anticlockwise rotor motions.

The fully wound mainspring in a typical watch can store enough energy reserve for roughly two days, allowing the watch to keep running through the night while stationary. In many cases automatic watches can also be wound manually by turning the crown, so the watch can be kept running when not worn, and in case the wearer's wrist motions are not sufficient to keep it wound automatically.^[2]

Preventing overwinding

Self-winding mechanisms would continue working even after the mainspring was fully wound up, putting excessive tension on the mainspring. This could break the mainspring, but even when it did not, could cause 'knocking' or 'banking'. The excessive drive force applied to the watch movement gear train made the balance wheel rotate with excessive amplitude causing the impulse pin to hit the back of the pallet fork horns. This made the watch run fast, and could break the impulse pin. To prevent this, a slipping clutch device is used on the mainspring so it cannot be overwound.

The slipping spring or 'bridle'

The 'slipping mainspring' device was patented by Adrien Philippe, founder of Patek Philippe, on 16 June 1863,^[3] long before self-winding watches. It was invented to allow simultaneous winding of two mainspring barrels. In an ordinary watch mainspring barrel, the outer end of the spiral mainspring is attached to the inside of the barrel. In the slipping barrel, the mainspring is attached to a circular steel expansion spring, often called the 'bridle', which presses against the inside wall of the barrel, which has serrations or notches to hold it.^[4]

As long as the mainspring is less than fully wound, the bridle holds the mainspring by friction to the barrel wall, allowing the mainspring to be wound. When the mainspring reaches full wind, its force is stronger than the bridle spring, and further winding pulls the bridle loose from the notches and it simply slides along the wall, preventing the mainspring from being wound further. The bridle must grip the barrel wall with just the right force to allow the mainspring to wind fully but not overwind. If it grips too loosely, the bridle will begin to slip before the mainspring is fully wound, a defect known as 'mainspring creep' which results in a shortened reserve power time.^[5]

A further advantage of this device is that the mainspring cannot be broken by excessive manual winding. This feature is often described in watch company advertising as an "unbreakable mainspring".

Automatic quartz or kinetic movement

More recently, electronic automatic quartz watches powered by arm movement have been developed. A weighted rotor turns a tiny electrical generator, charging an accumulator, such as a rechargeable battery or capacitor, which powers the quartz movement. This automatic quartz arrangement provides the accuracy of a quartz movement without the need to replace the battery or capacitor until it reaches the end of its life, which may be decades. This innovation was introduced by Seiko.

The watch winder

For people who do not wear their automatic watch every day, watch winders are available to store automatic watches and keep them wound. This is particularly advantageous if the watch has complications, like perpetual calendars or moon phases. A watch winder is a device that can hold one or more watches and moves them in circular patterns to approximate the human motion that otherwise keeps the self-winding mechanism working. Older mechanical watches should be kept wound and running as much as possible to prevent their lubricants from congealing over time, which diminishes accuracy. Modern mechanical watches generally use synthetic oil; whether or not synthetic oils congeal is a point of contention among watch experts. A full service (which involves disassembly, cleaning and re-lubrication) should be performed at least every five years to keep the movement as accurate as possible.

History

Perrelet: 1770

Abraham-Louis Perrelet working on a watch

The Swiss watchmaker Abraham-Louis Perrelet is said to have invented a self-winding mechanism in the 1770s for pocket watches. It worked on the same principle as a modern pedometer, and was designed to wind as the owner walked, using an oscillating weight inside the large watch that moved up and down. The Geneva Society of Arts reported in 1776 that 15 minutes walking was necessary to wind the watch sufficiently for eight days, and the following year reported that it was selling well.^[6] However recently, the case has been made against the Perrelet hypothesis by pointing out that the first drawing and accurate description of an automatic watch was created in 1778 by Hubert Sarton fr:Hubert Sarton and that it is uncertain that the Perrelet watch was actually based on a rotor principle [[1]] [[2]].

Breguet: 1780

Perrelet sold some of his watches to a contemporary watch making luminary, Abraham-Louis Breguet around 1780 who improved upon the mechanism in his own version of the design, calling his watches "perpetuelles" the French word for perpetual.^[7][8] They did not work reliably and Breguet stopped producing them around 1800.^[9]

'Bumper' wristwatches: 1923

First automatic wrist watch, Harwood, ca. 1929 (Deutsches Uhrenmuseum, Inv. 47-3543

Self winding mechanisms were more successful in wristwatches than in pocket watches because the arm moves more during daily activity than the torso. The first self-winding wristwatch did not appear until after World War I, when wristwatches became popular. It had been invented in 1923 by John Harwood, a watch repairer from Bolton^[10][11] who took out a UK patent with his financial backer, Harry Cutts, on 7 July 1923, and obtained a corresponding Swiss patent on 16 October 1923.^[12] The Harwood system used a pivoting weight which swung as the wearer moved, winding the mainspring. The ratchet mechanism wound the mainspring only when moving in one direction. The weight did not rotate a full 360°; spring bumpers limited its swing to about 180°, to encourage a back and forth motion.^[13] This early type of self-winding mechanism is now referred to as a 'hammer' or 'bumper'.

When fully wound, Harwood's watch would run for 12 hours autonomously. It did not have a conventional stem winder, so the hands were moved manually by rotating a bezel around the face of the watch. The watches were first produced with the help of Swiss watch manufacturer Fortis and went on sale in 1928. 30,000 were made before the Harwood Self-Winding Watch Company collapsed in 1931 in the depression. 'Bumper' watches were the first commercially successful automatic watches; they were made by several high grade watch manufacturers during the 1930s and 1940s.

Rolex

The Rolex Watch Company improved Harwood's design in 1930 and used it as the basis for the Rolex Oyster Perpetual, in which the centrally mounted semi-circular weight could rotate through a full 360° rather than the 300° of the 'bumper' winder. Rolex's version also increased the amount of energy stored in the mainspring, allowing it to run autonomously for up to 35 hours.

By the 1960s, automatic winding became standard in quality mechanical watches. Because the weighted rotor needed in an automatic watch takes up a lot of room in the case, increasing the thickness of the watch, some high end watch companies, such as Patek Philippe, continue to design manually wound watches, which can achieve a case thickness as low as 1.77 millimeters.

See also

• Automatic quartz
• Jewel bearing
• Miyota 8215

References

1. ^ Automatic Watch Movement Disassembly
2. ^ A notable exception is Seiko's wide range of watches based on the company's 7S26 movement, which cannot be hand-wound.
3. ^ Patent No. 58921
4. ^ "The Mainspring of an Automatic Watch". Glossary. TimeZone Watch School. http://www.timezonewatchschool.com/WatchSchool/Glossary/Glossary%20-%20Mainspring%20and%20Barr/Glossary%20-%20Mainspring%20and%20Barr/Glossary%20-%20Mainspring%20-%20Auto%20S/glossary%20-%20mainspring%20-%20auto%20s.shtml. Retrieved 2008-04-11.  Diagram showing operation of slipping mainspring.
5. ^ "Hints". British Horological Institute. http://www.undeadlinks.com/s.php?link=http%3A%2F%2Fwww.bhi.co.uk%2Fhints%2Fautomsp.htm&l=1. 
6. ^ Biography of Abraham Louis Perrelet
7. ^ Who invented the automatic watch?
8. ^ Timekeeping in Europe and China : Watches & Wonders timeline at Worldtempus.com^{[dead link]}
9. ^ Disher, Mark (August 28, 1999). "Automatic Winding - Some Significant Dates". TimeZone Classics Forum mailing list. http://www.timezone.com/library/wglossary/wglossary631697356826788351. Retrieved 2008-12-16. 
10. ^ [Bolton Museum]
11. ^ Press release by UK Patent Office on 80th anniversary of self-winding watch patent
12. ^ Brainy History - 16 October 1923
13. ^ "Bumper Automatic vs. Full Rotor Automatic". FAQ. FinerTimes.com. http://www.finertimes.com/asp/faqs.asp. Retrieved 2008-04-17. 

Hampel, H., Automatic Wristwatches from Switzerland, Schiffer, Atglen, 1994.

External links

• A visual guide to the gears that make bi-directional winding possible
• A detailed evaluation of the mechanics of the Seiko 7S26 automatic watch movement
• Ranfft, Roland. "Automatics for Everyone". About watches. Ranfft Watches. http://www.ranfft.de/uhr/info-e.html#M1. Retrieved 2008-04-17.  Photos of early automatic movements on German watch vendor site, including the Harwood
• Video of the making of an automatic watch from orient watch company
• Video of an automatic watch mechanism in a transparent case
• Video of a watch on a watch winder
• Compare watch winders