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Constant power The constant-force escapement 

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. But the multitalented device boasts other functions involving jumping displays. 

Constant power: the patented constant-force escapement

A portrait of Richard Lange appears. Display: A watch in the spirit of Richard Lange. This is followed by exquisite close-up views of a gold pocket-watch, its vibrating balance-wheel and its breathing balance-spring. Display: He turned fine watchmaking into precision watchmaking. The picture of the antique vibrating balance-wheel gives way – almost imperceptibly – to the vibrating balance of the RICHARD LANGE PERPETUAL CALENDER “Terraluna”. We witness the jumping of the patented constant-force escapement. A detailed view of the power-reserve indication follows. Display: 14 days of constant precision. Then a detail of the calendar displays. Display: perpetual calendar. The day-of-the-week indication jumps from Monday to Tuesday. Display: precisely jumping indications. We turn around the side of the case. Display: committed to precision and serving science. In an animation we see a multitude of stars, which deposit themselves on the large celestial disc on the movement side of the RICHARD LANGE “Terraluna”. Suddenly the moon, earth and celestial discs begin to turn in time-lapse, demonstrating the functioning of the orbital moon-phase display. From the rear view, the watch case turns over to the dial side. In a front view of the full watch-face the calendar indications change instantly from Tuesday 25th to Wednesday 26th October.

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 to produce a small amount of energy every ten seconds. This energy re-tensions the remontoir spring by an angle of 60 degrees. It corresponds to precisely the amount of energy that it will transmit to the escape wheel, the lever and the balance spring 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.

The constant-force escapement of the RICHARD LANGE PERPETUAL CALENDAR “Terraluna”

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.

Re-tensioning interval of 10 seconds as in the RICHARD LANGE PERPETUAL CALENDAR “Terraluna”

Re-tensioning interval of 60 seconds as in all ZEITWERK models 

Re-tensioning interval of one second as in the RICHARD LANGE JUMPING SECONDS

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