In the technical language of watchmaking, impulse is the transfer of energy from the escapement wheel to the balance wheel: without it, the oscillator stops. The entire history of mechanical escapements is, to a large extent, a history of attempts to make this transfer cleaner, more regular and less wasteful.
In the Swiss lever escapement — the industry standard for nearly two centuries — impulse reaches the balance wheel indirectly: the escapement wheel pushes the pallet lever, and the pallet lever pushes the balance wheel via the impulse pin. Contact occurs on sliding surfaces, with friction. It is robust, reliable, cheap to produce on an industrial scale; it is not particularly efficient.
Historical criticism of this system has generated alternative geometries. George Daniels conceived his independent double wheel escapement on the idea of reducing friction by bringing impulse almost into direct contact with the balance wheel, clearly separating the locking function from the impulse function. For decades it remained an atelier object: the tolerances required were at the limit of what could be manufactured. Bernhard Lederer took up that challenge with his Central Impulse Escapement, used in calibre 9012: two independent trains, two barrels, two remontoir d'égalité, two escapement wheels. Impulse to the balance wheel always arrives at constant energy, shielded from variations in the barrel. It won the Innovation Prize at the GPHG 2021; as to how many have been built, I have no verified data.
On the industrial production front, Grand Seiko developed the Dual Impulse Escapement for calibre 9SA5, operating at 36,000 vph. The conceptual distinction is clear: the locking and impulse functions are dissociated. The escapement wheel has an eight-armed star profile. In one direction, impulse reaches the balance wheel directly, without passing through the pallet lever; in the other, it passes through the lever as in a traditional system. Sliding friction is reduced by half the cycle. The practical result is greater energy efficiency, less wear on the contact surfaces, and a stated tolerance of −3/+5 seconds a day compatible with series production. The components are made using MEMS technology, which allows geometries and masses impractical with conventional machining.
The comparison with Omega's Co-Axial is frequent in specialist writing. The logic is similar — separating locking and impulse — but the geometric solutions differ. Anyone who has taken both apart knows they resemble each other in principle and differ in execution.
