Movements: The Spring Drive

Icon Invalid date

While traditional mechanical watchmaking has remained largely unchanged for the past 300 years - even with the introduction of new technology like quartz - there has been some significant innovations, especially when it comes to escapements, the set of components responsible for the accurate time-keeping of the watch. 

George Daniels started this movement with the invention of a new escapement, though it was very much derived from the ubiquitous Swiss lever escapement that features in nearly every mechanical watch around the world.

Yoshikazu Akahane took this a step further in 1977 with the invention of the Spring Drive caliber, though it wouldn't hit the market until 1999. While the Spring Drive may appear mechanical, like previous escapements, it is distinct from traditional mechanical watches by a rapidly spinning (not oscillating) glide wheel that is visible through the case back. While a traditional balance wheel “vibrates” back-and-forth, the glide wheel just spins rapidly in one direction.

(Note: If you haven't yet completed the Mechanical, Automatic, and Quartz articles in the Academy series, now would be a good time to click through and give yourself the context to fully understand this piece of technology.)

Fundamentals

All watches need a power source. Quartz watches are powered by a battery. Mechanical watches (manual and automatic) are powered by a mainspring, wound tightly around an arbor, and contained within a barrel. The energy that drives the wheels in a watch is derived from the tension created by this tightly wound spring trying to uncoil. It is forced to remain in its coiled state by a braking system that allows the power from the mainspring to drip, drip, drip through the movement bit by bit, so the hands move at the right speed to accurately track time. 

This “braking system” is otherwise known as the “regulating organ” of the watch (similar to the heartbeat for a human). Without it, the power from the mainspring would escape immediately. This also means the accuracy of the watch is entirely reliant on the accuracy of the escapement.

Normal Swiss Lever Escapements are comprised of four main components: A balance wheel, a hairspring (or balance spring), an anchor (or pallet), and an escape wheel. The faster the balance wheel and hairspring oscillates (vibrates back-and-forth) the more the watch is able to withstand shock without suffering a loss in accuracy. The normal balance wheel speed in the market these days is 28,800 vibrations per hour (vph). Speeds of 36,000 vph are not uncommon (and are especially common in some sports chronographs like the Zenith El Primero), but above that is rare.

In contrast, in a quartz watch a quartz crystal, which replaces the balance wheel and hairspring, vibrates at a remarkable 32,768 times per second when an electric current is passed through it by the battery. Quartz not only vibrates when an electric current is passed through its crystalline structure, but also emits an electric voltage when it vibrates (meaning it is piezoelectric). In a regular quartz watch, the quartz crystal is mounted next to an integrated circuit that delivers the battery’s electricity to the crystal, while also listening for the crystal’s feedback. It can recognize 32,768 vibrations and convert them into one electronic impulse, which is sent to the time-telling medium, be that an analog handset or a digital readout.

Spring Drive Technology

Spring Drive technology takes the best elements of both systems and blends them. A mainspring feeds its power to the glide wheel, which is attached to an eternal magnet that sits within an electromagnetic stabilization field connected to two coils that transmit the energy created by the spinning glide wheel to a quartz crystal This then feeds back its resonance to an integrated circuit that compares the speed of the glide wheel to the 32,768 oscillations of the quartz crystal to ensure the two are in sync. The integrated circuit then sends a message back to the magnetic field that is effectively the top pivot-point of the glide wheel, telling it to either intensify or reduce the strength of the field, which has the effect of either applying or releasing the brake on the glide wheel.

The timekeeping benefit is that the rate variation of the quartz crystal is far less than a traditional hairspring, and the visual benefit is that the seconds hand sweeps around the dial as the need for ticking has been removed by Spring Drive technology. The hand may be moving slightly faster or slightly slower, but it is always moving. The result is one of the most stunning aesthetic, and impressive technological developments watchmaking has ever seen.