Since the days of Galileo and his perpetual motion design, the world has dreamed of overcoming friction with endless kinetic energy. Physicists agree that perpetual motion is a myth, but you can dispel all mythological notions by seeing a watch with a Constant Escapement at Baselworld 2013.
A few years ago Girard-Perregaux announced a constant-force escapement based on a revolutionary concept founded on the elastic properties of a silicium buckled-blade.This component, thinner than a human hair, delivers constant impulses of energy to the oscillator and prevents diminishing torque provided by the barrel’s mainspring from altering the accuracy of the movement.
Just a few watch companies have found ways to achieve constant force using a so-called remontoire d’égalitée, but Girard-Perregaux provides a constant force escapement without a remontoire. We know of only one other watch with a constant force device, not being a remontoire d’égalitée and that is the Tensus by Heritage Watch Manufactory, a watch that we absolutely love here at Monochrome.
However, a few years after the initial launch of the idea, Mike Margolis, Girard-Perregaux U.S. President, told me, “Oh you will see our Constant Escapement in a watch at Basel!” Which watch you ask? Well, mum is the word. Incidentally, the name of the escapement refers to one of GP’s founders, Constant Girard, but the double entendre is intentional.
What is an escapement?
An escapement is the heartbeat of the watch and responsible for the ticking that you hear when holding the watch next to your ear. If you have a see-through caseback, you can see the balance wheel of a watch’s escapement oscillating.
The escapement parcels out the power from the barrel’s mainspring in precise increments, allowing the hands to move.
In a typical lever escapement (see image left), the energy of the mainspring comes through the gears to the escape wheel, pictured in blue.
All the power would immediately drain from the watch if not for the lever, also pictured in blue, with its pallets (pictured red).
The escape wheel provides impulse to the lever, which transfers that energy to the balance wheel (pictured gold).
The balance wheel spins to its limit, then returns to move the lever; spins the other direction, and returns to move the lever again.
Every time the balance wheel is in its center position, the lever moves allowing the escape wheel to move one click, which also propels the balance wheel in the other direction. At the end of a click, the pallets on the lever arrest the escape wheel until the balance wheel recoils. This common escapement style is a Swiss lever escapement.
There are two problems with a traditional Swiss lever escapement.
1. Decreasing amplitude when the power from the main spring decreases
1. For a mechanical watch, amplitude is the magnitude of change between the balance wheels oscillations. Every mechanical watch is adjusted to 5 or 6 isochronisms, for only one reason, and that reason is to let the watch run as precise as possible. After the watch is adjusted, it has a certain amplitude, and that amplitude changes during the course of unwinding the mainspring. When that happens, the chronometric rate drops, hence the watch no longer runs as precise as it should. The Constant Escapement provides consistent power, meaning a constant amplitude, and constant amplitude equals constant force – problem solved.
2. The other problem is friction. Typically, the lever touches the escape wheel, and its pallets slide against and meet the escape wheel’s teeth. In addition, friction is a problem with the lever contacting the balance wheel. The contact of these working parts requires oil and routine maintenance. Friction decreases accuracy, and the Constant-Force Escapement minimizes friction almost to the point of non-existence. The Constant-Force Escapement defies friction with the key ingredient of silicon for the buckled-blade. It also uses two escape wheels instead of one and a lever that contacts them with ultra-precise indexing, meaning there is increased technological precision in how the lever contacts the wheels. Friction becomes miniscule – another problem solved.
To understand this victory over decreasing power and friction, we need to understand how the Constant Escapement works.
The story begins with Nicolas Déhon who invented the movement while bending his train ticket. Boredom is the mother of invention. As Nicolas bent and released the ticket, he recognized the stored energy of the bent ticket that dissipated when the ticket unbent and then accumulated when it bent again. What he observed were the variations of stable and elastic properties, which GP employs in its thinner-than-a-human hair, silicon buckled-blade.
The buckled-blade is how Gerard-Perregaux achieves constant force. It fits between two fixed positions of the spring-frame, looking like a thin line at rest, and will buckle wave-like on either side of the impulse levers to release an infinitesimal millijoule with each oscillation. With such a small release, the power reserve is tremendous, and smaller amplitudes of shorter duration occur.
What comparison does justice to such a small amount of energy, a feather’s touch, a baby’s breath?
Nicolas had the idea, but it would take years before the material silicon could make it a reality. In 1999, Rolex first created a pre-silicon prototype of Dehon’s idea, but abandoned the project, leaving it to Girard Perregaux to realize in 2008. What Rolex lacked in silicon then, Gerard-Perregaux has in spades now. The silicon oxide of the buckled-blade is what allows continuous impulses to the balance wheel. The silicon’s contradictory properties of hardness and flexibility allow the blade to move from a stable state (stationary) to a metastable state (buckled), releasing energy until the mainspring depletes.
At first blush, the Constant Escapement may look like a traditional lever escapement complete with a balance wheel and balance spring, but notice the two escape wheels and two levers, plus the all-important buckled-blade. The left escapement wheel provides energy to the winding lever, which causes the blade to deform, providing a gradual accumulation of energy into the blade, which acts as an energy micro-storage unit to the point where the blade would flip to its opposite stable state. The small lug on the escape wheel tooth locks the blade and positions perfectly the fork of the impulse lever.
At the midpoint of the balance wheel’s cycle, its roller will make contact with the impulse lever fork and unlock the blade, which in return will flip to its opposite position. Doing so, it gives an impulse to the balance wheel and moves the winding lever the other direction. The other escape wheel will then bend the blade again. In traditional fashion, the balance wheel moves the winding lever between the two escape wheels much like a Swiss lever moves between the teeth of a single escape wheel. Far from traditional, the buckled-blade supplies this power. The impulse the blade gives is constant as it always releases the same energy when flipping. The given impulse remains unaffected as the mainspring winds down, providing the balance wheel constant amplitude. The escapement may look lever-like, but all similarities end with the buckled-blade.
A video might help:
The visual aspect of the Constant Escapement is striking. The architecture for the Constant Escapement is a paradigm leap from what has gone before. Avant-garde materials and advanced manufacturing technology permit these unique shapes, which have tolerances in the micrometer range. In terms of materials, besides the silicon of the blade, nickel comprises the two levers. In terms of technology, LIGA (an acronym derived from the German words for lithography, electroplating, and molding), a process first used for medical applications in the 1980s, creates flawless components, and innovative shapes become possible. Using photo-lithography and electroforming, Girard-Perregaux is able to make very accurate shapes with exceptional surface quality. The result looks like nothing you have ever seen inside a watch and makes for a watch unlike any other.
Imagine the 1966 Perpetual Calendar with the Constant Escapment. It will have stellar accuracy for its perpetual calendar and utilize a groundbreaking technology. Gerard Perregaux claims that the escapement has been tested to 7.2 hz (or 25,920 vph), and they believe that the design’s inherent accuracy makes a high frequency optional, if not superfluous. For this first watch, Girard-Perregaux plans on 21,600 vph. When I travel to Basel for the fair, I will certainly provide an update on the identity of this mystery watch.
This article is written by Max E. Reddick, contributing writer for Monochrome Watches.