Gear Mechanism Used in Wrist Watches
Gear Mechanism Used in Wrist Watches
Gear Mechanism Used in Wrist Watches
The underside view of a Gruen automatic watch with a transparent case back, showing an ETA 2824-2. The rotor and the balance wheel are plainly visible
An automatic or self-winding watch is a mechanical watch, whose mainspring is wound automatically by the natural motion of the wearer's arm, providing energy to run the watch, to make it unnecessary to manually wind the watch. Most mechanical watches sold today are self-winding.
How it works
A self-winding watch movement is similar to a manual movement with the addition of a mechanism powered by an eccentric weight which winds the mainspring.[1] The watch contains a semicircular 'rotor', an eccentric weight that turns on a pivot, within the watch case. The normal movements of the user's arm and wrist cause the rotor to pivot back-and-forth on its staff, which is attached to aratcheted winding mechanism. The motion of the wearer's arm is thereby translated into the circular motion of the rotor that, through a series of reverser and reducing gears, eventually winds the mainspring. Modern self-winding mechanisms have two ratchets and wind the mainspring during both clockwise and counterclockwise rotor motions. The fully-wound mainspring in a typical watch can store enough energy reserve for roughly two days, allowing automatics to keep running through the night while off the wrist. 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
A problem that had to be solved with self-winding mechanisms is that they continued working even after the mainspring was fully wound up, putting excessive tension on the mainspring. This could break the mainspring, but even when it didn't, it caused a problem called 'knocking' or 'banking'. The excessive drive force applied to the watch movement gear train made the balance wheel rotate with too much amplitude, that is too far in each direction, 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.
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 hascomplications, 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 its 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
The Swiss watchmaker Abraham-Louis Perrelet invented a self-winding mechanism in 1770 for pocket watches. It worked on the same principle as a modernpedometer, 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 fifteen minutes walking was necessary to wind the watch sufficiently for eight days, and the following year reported that it was selling well.[6]
[edit]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]
Self-winding mechanisms by August Ritter von Lhr of Austria patented in the 1880's [10]
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.