|
|
|
The
underside view of an automatic watch with a transparent case
back. The rotor and the balance wheel are plainly visible
|
How
an Automatic Watch Works
To accomplish this, the watch contains a fan-shaped rotor (a/k/a
a weight or an oscillating mass) within the watchcase. 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 reversers 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 development of 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. The slipping bridle
on the outer end of the mainspring is illustrated here:
|
|
|
In the
automatic winding watch, the mainspring must be designed to
prevent over winding (with continuation of automatic winding)
when the spring is fully wound.
This is
usually accomplished in contemporary watches with a slipping
bridle on the outer end of the mainspring as illustrated above
(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.
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.
The Auto-Quartz or Kinetic Movement
A more recent evolution of the automatic watch uses a self-winding
mechanism to charge a battery or capacitor which in turn powers
a quartz movement. This automatic quartz arrangement provides the
accuracy of quartz without the need to replace the battery or capacitor
until it reaches the end of its life, which may be decades.
History of Automatic Watches
Perrelet
In 1770 the Swiss watchmaker Abraham-Louis Perrelet invented a self-winding
mechanism for fob watches. It worked on the same principle as a
modern pedometer, 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.
Breguet
Perrelet sold some of his watches to a contemporary watch
making luminary, Abraham-Louis Breguet who improved upon the mechanism
in his own version of the design, calling his watches "perpetuelles"
the French word for perpetual and possibly the source for Rolex's
name for its automatic movements, the "Perpetual").
Harwood
The mechanism was more successful in wristwatches because the rotor
could operate every time that the owner moved his or her arm. However
the first version did not appear until the 20th century. It was
invented by a watch repairer from the Isle of Man named John Harwood
in 1923, who took out a UK patent with his financial backer, Harry
Cutts, on 7 July 1923, and a corresponding Swiss patent on 16 October
1923. The Harwood system used a pivoting weight, which swung as
the wearer moved and which in turn wound the mainspring. When fully
wound, the watch would run for 12 hours autonomously. It did not
have a conventional stem-winder, so the hands were moved manually
by rotating a bezel around the face of the watch. The watches went
on sale in 1928 and 30,000 were made until the company collapsed
in 1931 as a result of the Great Depression.
Rolex
The Rolex Watch Company had taken up the 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 degrees rather than the 300 degrees of the original design.
Rolex's version also increased the amount of energy stored in the
mainspring, allowing it to run autonomously for up to 35 hours.
Omega
Most mechanical watches sold today are automatic. A notable exception
is the Omega Speedmaster Professional Moonwatch, the model
used by NASA astronauts during the Apollo Program. Reportedly NASA
assumed that the automatic winding mechanism was based on pendulum
action like Harwood's original design, requiring either a gravity
field or constant acceleration. The weightless environment therefore
raised doubts about the ability of an automatic watch to wind itself.
In fact a full 360-degree winding mechanism should work even better
in low or zero gravity, where the friction experienced by the mechanism
is lower. The rotor can thus move longer and transfer more energy
into the spring. The rotor is in any case easily activated by momentum
and not dependent on gravity.
Patek
Philippe
Because of the fact that a manually wound wristwatch does not require
the weighted rotor which is necessary for an automatic watch, some
extremely fine watch companies, such as Patek Philippe, continue
to design manually wound watches, which can achieve a case
thickness as low as 1.77 millimeters.
