How it Works: The Seiko Spring Drive?

The history of horology is one of constant innovation. Sometimes advances progress incrementally, involving a slow but steady fine-tuning of accepted practices over time. But very occasionally, a system or a process will come along that changes the landscape completely, setting all new standards for the industry.

Quartz technology was one such leap forward—and one which was so damaging to the traditional Swiss watchmaking houses in the 1970s that around two thirds of them were bankrupted during what became known as the quartz crisis.

Ironically, the biggest player behind the development of those new electronics, Seiko, is also responsible for another, far more recent revolution.

The Spring Drive has been called one of the most ingenious and efficient inventions ever in the world of timekeeping. But its unique take on the art of the watch movement still remains somewhat mysterious, so we have put together this article to try and explain exactly how it works.

Solid Foundations

Back at the height of the quartz crisis, when it became obvious it wasn’t something that was just going to blow over, the big conventional watchmaking brands were forced to engage and create electronic calibers of their own. One of the last to jump on the bandwagon was Rolex, who brought out the Cal. 5035 and Cal. 5055 inside their Oysterquartz models. Still recognized today as two of the most accurate movements ever made, a great deal of their success hinged on Rolex retaining as much of their traditional mechanisms as possible, containing parts that had been honed to near perfection over generations.

Seiko has taken the same approach. Around 80% of the Spring Drive—the mainspring, the rotor, the gear train, etc.—are all practically identical to what you would find in one of the brand’s high end mechanical calibers. In fact, just about the only appreciable difference lies in what Seiko has done with the heart of the movement, the escapement.

The component that manages the release of energy from the mainspring in a conventional watch has been replaced in the Spring Drive with something called the Tri-synchro regulator.

The Tri-synchro Regulator (TSR)

As its name suggests, the TSR is used to regulate three different kinds of power; kinetic, electrical and electromagnetic.

Like a traditional mechanism (and unlike a purely quartz watch), the Spring Drive gets its energy from the mainspring, which is wound, as normal, by either the motion of the wearer’s wrist or by turning the crown. What Seiko call the Magic Lever system, actually invented way back in 1959, uses the energy from each direction of the rotor’s swing, clockwise and counterclockwise, to greatly increase the efficiency of the winding system.

That mainspring is connected to the gear train as per usual. However, uniquely to the Spring Drive, at the other end of the gear train is not a balance wheel turning back and forth, but a glide wheel which turns continuously in one direction only.

So far, so simple. But there has to be something to prevent all that power from the mainspring just wildly spinning the glide wheel until it’s unwound completely. That is normally the job of the escapement, which uses a pallet assembly to release the energy in stages (and produce the tick-tock sound we all know).

In the Spring Drive, a permanent electromagnet fixed to the glide wheel, called a stator, acts as a brake, slowing the rate down precisely but without generating any friction. That process simultaneously generates an electrical current, which runs through an Integrated Circuit (IC) and a quartz crystal oscillator. This self-generating power supply is the reason there are no need for batteries with the Spring Drive.

That quartz crystal is a piezoelectric material, meaning it vibrates at a precise rate when a voltage is applied to it—in this case, 32,768 times per second. The frequency is used as a reference signal that ultimately controls the speed of the glide wheel.

The IC measures the information provided by the stator about how fast the glide wheel is spinning and compares it to the information from the quartz crystal, and by measuring the disparity between the two, decides on how much electromagnetic braking is required to slow the wheel to keep it in line with the oscillator. And it does it eight times a second.

The Benefits

The Spring Drive is really the best of both worlds. It combines the incredible precision of quartz with the perpetual energy of a conventional self winding mainspring. That really leaves it in pretty much a group of one, neither fully electronic nor fully traditional.

In addition, with almost all of the components being mechanical, they are wonderful to watch in action and you will find a number of Seiko watches, particularly the Grand Seiko range, feature display case backs.

But what is going on up front is just as appealing as the inner workings. Because of the nature of the power delivery in the Spring Drive, basically a continuously spinning wheel rather than the start/stop of a regular escapement, it produces a silky smooth sweep to the seconds hand unlike any other watch you will find. Even a very high beat creation such as Zenith’s El Primero and its 36,000vph can’t match the glide. And, without that familiar ticking soundtrack, the movement is also completely silent; the ‘Quiet Revolution’ is how Seiko describes it.

On top of all that, with an escapement being about the hardest working element in a classic movement, it is the one in need of the most attention come servicing time. With the Spring Drive, although maintenance is still very much a necessity because of all the traditional components, the intervals can be longer.

By combining the most successful elements from several hundred years of development and marrying them to a real technological revolution, Seiko has created what is possibly the finest watch movement ever made.

With the brand dictating the power reserve must be at least 72-hours, and with an accuracy of +/- 15 seconds a month (although Seiko advertises about 1 second a day, and wearers claim they are even better than that), they are as near to the perfect timekeeper you will find outside of digital watches.

Although the Spring Drive is celebrating its 20th anniversary this year, there is still nothing that comes close to its performance—and it is likely to stay that way for some time.