Spring Drive is one of the most widely known of all the innovations created by Seiko in its entire history – but perhaps also the most misunderstood. This is partly because nothing like Spring Drive exists anywhere else in modern watchmaking: a watch regulated by a quartz oscillator, but one which is driven by a mainspring, has a completely conventional gear train, and has no battery.
It’s easy to confuse Spring Drive with another technology: autoquartz movements, which are also made by Seiko in their Kinetic line of wristwatches. A Kinetic watch is a standard quartz watch, with a twist: it has a mechanical rotor that powers a tiny electrical generator, which, in turn, tops off the rechargeable battery in the watch. In every other respect, however, the Kinetic is a standard quartz watch (albeit one with a battery that needs replacing only infrequently). And, as in every other quartz watch, the hands of a Kinetic watch are moved by a stepper motor, with a seconds hand that advances in one-second jumps.
When you look at a Spring Drive watch, the first indication you have that you’re not looking at a conventional quartz watch, or at a conventional mechanical watch, is the seconds hand: a Spring Drive seconds hand sweeps smoothly around the dial in continuous motion, rather than advancing in discrete steps. Even in a mechanical watch, the seconds hand moves in jumps, rather than smoothly, as the seconds hand’s motion is linked to the action of the escapement (the seconds hand jumps forward every time the escapement unlocks).
Here’s how Spring Drive works. The mainspring of a Spring Drive watch drives a standard gear train. At the end of the gear train, there is a small disk – the Spring Drive glide wheel. At the center of the glide wheel is a small permanent magnet, which turns in between two tiny electromagnets connected to wire-wrapped coils; the glide wheel acts as the rotor of an electrical generator. A quartz timing package connected to the coil system monitors the speed of rotation of the glide wheel, and feeds electricity back to the electromagnets, which exert a braking force on the glide wheel – just enough to keep the glide wheel rotating exactly eight revolutions per second. Since the glide wheel turns smoothly, the entire gear train advances with a smooth, continuous motion – visible in the gliding movement of the seconds hand, which is the signature of Spring Drive.
Spring Drive movements must be made to a very high degree of mechanical precision, and a great deal of research was necessary, over many years, to develop circuits that were efficient enough in power production, as well as low enough in energy consumption, before Spring Drive could be introduced. Here we dive deep into Seiko’s struggle to turn a great idea into a working and refined reality.
Top photo: (bottom right) an early prototype from 1982; (top right) a second prototype from 1993; (left) a third wristwatch-cased prototype.