Technology and Function
of the Mechanica M
2
70
71
The influence of temperature is, however, not the only interfering
factor. Change in position as well as shocks are important factors,
particularly for pocket and wristwatches. Like any pendulum
*
, the
balance
*
is exposed to the effects of gravity. Ideally, gravity should
influence the even oscillation of the balance
*
as little as possible. To
achieve this, the oscillating system—comprising balance and balance
spring
*
—needs to be poised as precisely as possible.
While in previous times the unbalance
*
was compensated for by
adjusting the numerous weighted screws and adapting the balance
spring, today balance wheels are generally finely poised in fully
automatic manner using computer-controlled laser trimming. This
takes place with a fully assembled balance spring, since it heavily
influences the balance of the oscillating system. Balance wheels are
thus always considered a unit together with the balance spring
*
.
A non-powered balance would oscillate practically isochronously. This
means that the length of the oscillations is independent of the
amplitude
*
(or the angle of rotation). All efforts on the part of the
watchmaker concentrate on retaining this isochronism
*
.
It is achieved by reducing the following causes of the changes:
◊
friction of the pivots
◊
insufficient balance (unbalance) of balance and balance spring
◊
influence of the escapement
*
◊
temperature
◊
magnetism.
In watchmaking, oscillation frequency is defined by the number of
semi-oscillations (either a »to« or a »fro«) the balance makes per
hour. Every Semi-oscillation corresponds to the advancement of an
escape wheel tooth (except for the Chronometer escapement).
The frequency of the balance of your Mechanica M2 is 18,000 vph
(vibrations per hour), which corresponds to 2.5 Hertz.
The Escapement
The escapement is the passage between the Oscillating organ
*
and
the Gear train
*
. The escapement not only has the task of blocking
the Gear train from running uncontrollably and only allowing it to
move forward in steps, it is also responsible for driving the oscillating
system. So that it can oscillate with as little disturbance as possible, it
is necessary for the energy transmission
*
to take place as evenly as
possible. To guarantee that the balance can move fully freely during
the other oscillation, the impulse should take place through the
smallest possible amplitude
*
of oscillation.
Assuming that forces of friction like
◊
bearing friction
◊
air friction
◊
inner friction of the balance spring
*
don’t change, the result will be a constant amplitude of the
oscillation system (rotational motion of the balance).
TTheoretically, the oscillating system is not influenced if the impulse
of the balance takes place exactly when it has reached its greatest
rotational speed. In this state, the balance spring has fully released its
tension. Since this corresponds to the balanced position when the
balance is idle, this point is called Dead center
*
. Ideally, the balance
should oscillate evenly to both sides of Dead center.
As previously described in the section on the development of
escapements
*
, numerous escapements were invented to achieve
the most even distribution of energy. Today, it is the Swiss lever
escapement
*
that has asserted itself in portable mechanical
timepieces.
