An automatic watch (also called a self-winding watch or, in Rolex movements, "perpetual") is a mechanical watch, typically with a balance wheel escapement, whose mainspring is wound by the motion of the wearer's arm automatically, instead of having to be wound manually every day.
How it works
To accomplish this, the watch contains a fan-shaped rotor (a/k/a a weight or an oscillating mass) 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 a ratcheted 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. The fully-wound mainspring in a typical watch can store enough energy reserve for roughly two days, however some models made specifically to have longer power reserves can last longer. Many automatic watches can also be wound manually by turning the crown (a notable exception is Seiko's wide-range of watches based on the company's 7S26 movement, which cannot be hand-wound).
Why it doesn't over-wind itself
On June 16, 1863, Adrien Philippe (of Patek Philippe) is credited with Patent No.58941, for the "slipping mainspring". This particular invention allowed the simultaneous winding of two or more mainspring barrels, certainly a different invention with a different purpose. However, the technology of his invention is said to be the foundation for the development of self-winding wristwatches.
The Slipping Spring
This "slipping" spring allows the mainspring to slide or slip a few degrees relative to the inside of the barrel while still staying fully wound. The end of the slipping spring moves from one groove to another on the inside the barrel, stopping each time, and thus keeping the spring under constant tension.
This attachment of spring steel is sometimes referred to as a “bridle”. This bridle slips along the barrel wall before excess pressure is passed to the going train and causing a defect known as “banking.” Banking occurs when the balance amplitude is too high and the impulse jewel strikes the back of the horns of the pallet fork. The “bridle” must also grip the barrel wall sufficiently to not slip down either too rapidly, or too slowly, a defect known as “mainspring creep” which results in a shortened reserve power time. http://www.bhi.co.uk/hints/automsp.htm The slipping bridle on the outer end of the mainspring is illustrated here. (1). the bridle (in the barrel), (2) maintains outward pressure on the outermost coil of the mainspring (3). At less than full wind, the bridle pressure causes the outer tip of the spring to catch in a notch in the barrel wall (4) and maintain its position. As the mainspring reaches full wind, the outer end of the spring jumps out of the notch and releases tension by slipping across the smooth section of the barrel wall (5) until it catches in the next notch.
This "slipping" spring allows the mainspring to slide or slip a few degrees relative to the inside of the barrel while still staying fully wound. The end of the slipping spring moves from one groove to another on the inside the barrel, stopping each time, and thus keeping the spring under constant tension.
This attachment of spring steel is sometimes referred to as a “bridle”. This bridle slips along the barrel wall before excess pressure is passed to the going train and causing a defect known as “banking.” Banking occurs when the balance amplitude is too high and the impulse jewel strikes the back of the horns of the pallet fork. The “bridle” must also grip the barrel wall sufficiently to not slip down either too rapidly, or too slowly, a defect known as “mainspring creep” which results in a shortened reserve power time. http://www.bhi.co.uk/hints/automsp.htm The slipping bridle on the outer end of the mainspring is illustrated here. (1). the bridle (in the barrel), (2) maintains outward pressure on the outermost coil of the mainspring (3). At less than full wind, the bridle pressure causes the outer tip of the spring to catch in a notch in the barrel wall (4) and maintain its position. As the mainspring reaches full wind, the outer end of the spring jumps out of the notch and releases tension by slipping across the smooth section of the barrel wall (5) until it catches in the next notch.
The Display Case back
On some automatic watches the rotor and its action are visible through a transparent case back, called a display back or exhibition back. In these watches, the rotors are often engraved or decorated in some way. Rolex is one of the few automatic watch manufacturers that traditionally eschews the transparent case back, mainly for enhanced water resistance.
On some automatic watches the rotor and its action are visible through a transparent case back, called a display back or exhibition back. In these watches, the rotors are often engraved or decorated in some way. Rolex is one of the few automatic watch manufacturers that traditionally eschews the transparent case back, mainly for enhanced water resistance.
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 had complex or 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. A mechanical watch should be kept wound and running as much as possible to prevent its lubricants from congealing over time, which diminishes accuracy. 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.
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 had complex or 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. A mechanical watch should be kept wound and running as much as possible to prevent its lubricants from congealing over time, which diminishes accuracy. 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.
Article Source:http://en.wikipedia.org/wiki/Automatic_watch
