From Watches Wiki
Drive mechanism of a watch
Who invented the watch movement?
The following discussion is intended to illustrate the basic principle of a mechanical watch. Strictly seen it does not apply to all types of watches and constructions, because there can be several differences. But the basic idea remains the same, because the watch has not been invented by a single person, but has continuously evolved, refined and improved over several centuries by a number of contributions. One can look at the watch, therefore, as a concerted development effort of all mankind.
The process of power transmission from winding to the hands
Consider first the image shown at the top right-hand corner. For reasons of clarity the drive mechanism is lined up from top to bottom - one wheel is driving the next.
With automatic watches the transmission begins at the rotor, which makes use of the forces caused by movement changes at the wrist and transfers it to the mainspring and the barrel. Or in manual winding watches the force is generated by manual winding.
The translation to the individual hand displays
The gear train translates the momentum into the different speeds: Seconds, minutes, hours, etc. The picture on the left hand side shows the translation scheme of the gear train:
- Z1 is the minute wheel, on the axis of which is the hour hand.
- Z3 is the third wheel, Z5 the fourth wheel (seconds wheel), (possibly with the seconds hand).
- All these wheels are usually riveted on their shafts Z, Z2, Z4, Z6.
The movement construction
In this picture a movement plate (main plate) is shown in which the gears of the gear train and barrel, balance wheel and so on are fitted. To reduce the friction the shafts of the wheels are fitted in so-called jewels.
The oscillation system
The characteristic ticking of a mechanical watch is the acoustic feature of the oscillation and escapement system of a watch movement .
This oscillating system consists of the balance wheel , which is turning on the balance staff, the balance spring , and a regulating device, usually called regulator. Hereby the oscillation of the balance spring can be precisely adjusted, so that the desired correct rate of the watch can be attained.
The exact rate is based on the maximum possible uniformity of the back-and-forth oscillation of the balance wheel , which must also be balanced as accurately as possible.
Without a steady, precise dosed energy supply this regulated organ however would cease to move. Therefore, it is constantly fed by the force coming from the barrel and via the gear train , in accordingly reduced doses. The escapement transfers this force via the escape wheel , the lever  and roller  further to the oscillation system. In a sophisticated flow by inhibiting and releasing the lever grips into the escape wheel in such a way that the movement is always pulsating in the same measure of time (see animation on the right hand side).
Hereby, depending on the oscillation frequency of the balance wheel (eg, 28,800 A/h), a precise base unit is given on which the rest of the arithmetic of gear ratios and hence the precision of the watch is based. Also the measuring accuracy of mechanical chronographs directly depends on this background (for details see: The measuring accuracy of chronographs).
- WatchTime (watch technology) - Thomas H. Ernst (German)