Or more commonly referred to as the Automatic Watch. Most Mechanical Watches nowadays are equipped with a self-winding mechanism. In other words the mainspring is wound automatically by the natural swinging motion of the wearer's arm.
You might be wearing one at the very moment... so how does it work?
The watch contains a semi-circular rotor - depicted in the image of the Perrelet Watch. This rotor is an eccentric weight that turns on a pivot within the watch case. Natural movement of the wearer's arm causes the rotor to swing to and fro on its staff. The staff is attached to a ratcheted winding mechanism. The motion of the wearer's arm is transformed into a circular motion of the rotor that by a series of reverser and reducing gears winds the mainspring. Most modern automatic luxury watches have two ratchets and thus wind the mainspring during clockwise and counterclockwise rotor motion.
Once the mainspring is fully wound, a regular watch can store enough power reserve for two days. Most automatic watches can be wound manually if the watch is not worn sufficiently to keep the mainspring wound. Another alternative to keep automatic watches running is the use of a watch winders.
Abraham-Louis Perrelet invented the self-winding mechanism ,in 1770 ,for pocket watches. The watch wound as the wearer walked. An oscillating weight inside the hefty pocket watch moved up and down. Perrelet invention was quite the rage in 1776. The Geneva Society of Arts reported that only a 15 minute walk was enough to wind the watch sufficiently for eight days. In 1777 the automatic pocket watches were selling quite nicely.
Breguet improved on Perrelet mechanism calling his automatic pocket watches "perpetuelles"
Although the first wrist watch was introduced by Patek Philippe in 1868, the automatic rotor for wrist watches was not invented until 1923 by a watch repairer from the Isle of Man named John Harwood. This self-winding mechanism was an improvement as the wearer only had to move his arm not take a walk. Harwood's system utilized a a pivoting weight which swung as the wearer moved, winding the mainspring. The ratchet mechanism only swung in one direction and were stopped at 180 degrees by spring bumpers to encourage the back and forth motion. This early type of automatic watch is now known as a "bumper". Fully wound the bumper would run for 12 hours. The "bumper" did not have a stem winder and so the hands were moved manually by rotating a bezel around the face of the watch. The Harwood Self-Winding Watch went on sale in 1928 and 30,000 were produced until the company collapsed in the Great Depression.
Rolex improved Harwood's design in 1930 and used it for the basis of the Rolex Oyster Perpetual which had a mounted semi-circular weight which could rotate a full 360 degrees. Rolex Oyster Perpetual had 35 hours of stored energy.
Omega is the only Automatic watch that utilizes a Co-Axial movement which is a double Axial escape wheel, a lever with three pallet stones and impulse stone on the balance roller, together with a free sprung balance. This system reduces sliding friction compared with the lever escapement inorder to promote greater accuracy over the course of time.
Watch Companies like Concord still create manually wound watches and can be produced
with exceptionally thin watch cases like the slender Concord Delirium pictured above which has a Watch Case of just 6mm. This type of thickness cannot be achieved by an automatic watch as the rotor occupies space within the watch case. However with the knowledge that ones watch is being wound as you wear it does afford a certain peace of mind.
By: R Van Halem