The purpose of a constant-force escapement in a mechanical watch is to provide the escapement with a consistent flow of power, regardless of whether the watch is fully wound or nearly unwound.
THE CONSTANT-FORCE ESCAPEMENT MECHANISM
WITH THE PERSEVERANCE OF A MARATHON RUNNER
With two strong springs, the twin mainspring barrel of the RICHARD LANGE PERPETUAL CALENDAR “Terraluna” provides a power reserve of 14 days. The LANGE 31 tops this with 31 days. Like a marathoner, this constant-force escapement consumes a considerable amount of energy and – even more importantly – must deliver its power in doses.
If fully wound, the torque delivered by this high-energy mainspring barrel would be much too high to be transferred directly to the escapement. And if its torque declines when it approaches the unwound state, the accuracy of the watch would deteriorate. To keep the rate of the watch stable for the entire power-reserve period, a patented constant-force escapement is integrated between the twin mainspring barrel and the escapement of both watches.
It causes the twin mainspring barrel (1) to produce a small amount of energy every ten seconds. This energy re-tensions the remontoir spring (2) by an angle of 60 degrees. It corresponds to precisely the amount of energy that it will transmit to the escape wheel (3), the lever (4) and the balance spring (5) within the next ten seconds.
Since the remontoir spring always releases exactly the same amount of energy, the watch is powered with the same torque every day. The result is a constant amplitude and thus an especially high degree of rate accuracy. The remontoir spring of the constant-force escapement and the balance spring are both manufactured in-house and can thus be optimally paired with the movement.
LIKE THE POUNCE OF A PUMA
In the ZEITWERK models, the constant-force escapement not only supplies the escapement with a steady flow of power, but it also generates the switching impulses needed to advance the jumping numerals. Like a puma preparing to pounce, the constant-force escapement must deliver a strong burst of energy.
It is designed to execute a re-tensioning cycle precisely every 60 seconds. For a brief moment, the full torque of the mainspring barrel is released for re-tensioning. Instantaneously, this burst of power is used to switch the numeral discs.
LIKE A HOVERING HUMMINGBIRD
In the RICHARD LANGE JUMPING SECONDS, the constant-force escapement and the jumping seconds mechanism are assigned to separate but firmly interconnect wheel trains. Like a hummingbird, which needs to beat its wings at high frequencies to hover in mid-air, the constant-force escapement must perform many fast-paced switching steps with one-second precision.
The mainspring barrel is briefly set free once a second. In the process, it moves the seconds hand forward by one second and incrementally tensions the spring of the constant-force escapement. All the while, the watch runs very precisely thanks to a constant delivery of force.