Automatic winding (also called self-winding) uses physical motion of a watch (usually rotation) to turn the barrel and wind the mainspring. It is differentiated from traditional hand winding, also called "manual" or "keyless" winding.
With this type of winding, a rotating weight segment (rotor), which is moved by the motions of the watch, causes the self-winding of the movement. The generally accepted design principle is that of the central rotor, though some movements use a micro-rotor. There are unidirectional and bi-directional winding mechanisms.
Abraham-Louis Perrelet is considered the inventor of the automatic winding at pocket watches. In the 1920's, when the wristwatch was preparing for its triumph, the Englishman John Harwood applied this automatic winding concept to wristwatches. Wristwatches make automatic winding more useful because arm movements deliver the required amount of kinetic energy, unlike comparably static pocket watches.
The automatic wristwatch concept came to the mass market when Rolex presented its "perpetual" winding in 1931, which made manual winding entirely unnecessary. Over the next 40 years, nearly every watch manufacturer introduced their own automatic winding mechanism, and this is the dominant system today.
Albert Pellaton developed another system of automatic winding, which applied for a patent in 1946 and was completed in 1950: the Pellaton winding. One more version of the automatic winding was the "Pump-Action" automatic by Wyler. This solution could not win through.
Before self-winding watches were worn in space, there was a short discussion whether or not due to lack of gravity there would be enough kinetic energy for the mechanism to function. The first watch in space, the Omega Speedmaster Professional ( "Moon Watch"), still featured manual winding. Finally, the Fortis Official Cosmonauts Chronograph, worn by Russian cosmonauts in space, proved without doubt that normal everyday body movements were sufficient to supply the required energy.
Many early automatic winding systems did not rotate freely 360 degrees. Instead, the weight segment rotated a shorter distance before reaching a spring and a stop at each end. These so-called "bumper" or "hammer" winding systems were functional but produced an odd feeling on the wrist. Although they were widely produced in the 1950's, they quickly fell out of vogue and were replaced by freely-rotating winding mechanisms once patents expired. By the late 1960's, no more bumper automatics were produced.
In 1942 the ebauche movement manufacturer Felsa delivered the first bidirectional winding system with its "Bidynator". Eterna eliminated various problems in the rotor bearing by using a miniature ball bearing since 1948 and adopted geared bidirectional winding shortly afterwards. Seiko developed an entirely different method of bidirectional winding, delivering their "Magic Lever" system in 1959.
Today, the majority of automatic watches feature bidirectional winding, though uni-directional winding is still fairly common. The current trend is a return to uni-directional winding, citing improved efficiency and reliability. Of these, the majority wind clockwise but many wind counter-clockwise, creating an issue for users of electronic watch winders.
Throughout the 1960's, a competition developed to deliver the first automatic chronograph movement. The El Primero by Zenith/Movado (with a central rotor) was first to market in 1969, followed just 60 days later by the micro-rotor Chronomatic from Breitling/Heuer (Calibre 11). Seiko also delivered their automatic 6139 chronograph in 1969, and the Lemania 5100 and popular Valjoux 7750 followed in 1973 and 1974, respectively.
Today, there are many automatic chronograph mechanisms on the market.
Hand winding automatic movements
Many automatic movements may also be hand-wound. There is some debate as to whether this can damage the keyless works mechanism and clutches, however, and should be avoided with certain movements, including the popular ETA 2824-2.
- Main article: Central rotor
The most widespread automatic winding technology places the weight segment on a pivot located at the center of the movement. The segment then rotates around the outer edge of the movement. This typically requires clearance all around the top of the movement for a free-rotating segment, though a bumper central-rotor automatic is also possible.
Central rotors have posed challenges for alarm watches like the Jaeger-LeCoultre Memovox: The initial models use a bumper to allow the alarm hammer to pass through, though later movements use a center hammer inside a wider than normal rotor pivot.
- Main article: Peripheral rotor
Some manufacturers (notably Citizen and Patek Philippe) have produced geared peripheral winding mechanisms. These do not have a central pivot but mount the weight segment on a ring that rotates around the outside of the movement. These proved troublesome and were abandoned in favor of central- or micro-rotor designs.
- Main article: Micro-rotor
Although most automatic winding mechanisms use a weight segment along the entire periphery of the movement, some use a smaller inset rotor or "micro-rotor". This concept has been used since the invention of automatic winding and remains in limited use today. Micro-rotors are often employed in ultra-thin movements or where a full rotor would interfere with other complications.