Spring Drive was, for a long time, something I thought I understood, at least on a rudimentary level. My knowledge came primarily from research I had done myself, as well as explanations I’d gotten from enthusiasts who themselves likely only had a cursory understanding of the movement’s most basic mechanics. But it wasn’t until I visited Japan last year and had an opportunity to get a closer look at Spring Drive that I truly grasped its mechanical genius.
Grand Seiko’s 9R Spring Drive is the brand’s most groundbreaking movement family, and it’s one that’s totally unique to Grand Seiko. As their engineers explain it, at its most basic Spring Drive combines the best of mechanical watchmaking and the best of quartz timekeeping to create a state of the art caliber that lacks the weaknesses inherent to both of these movements. The result is a watch with quartz-like accuracy of + or – 1 second a day, coupled with the unlimited energy potential of a mechanical watch powered by a mainspring.
Now, I know that only scratches at the surface, so let’s do a deep dive into the mechanics of Spring Drive.
Let’s start with the power source. Like a mechanical movement, Spring Drive movements get their energy from a mainspring, not a battery, and this mainspring is wound up either by a rotor or manually by hand through the crown. The mainspring drives a standard gear train — again just like the sort you’d see in a mechanical watch.
But it’s at the end of that gear train that we come to what makes the Spring Drive movement truly unique. Here, Grand Seiko uses a proprietary piece of tech they’ve dubbed the Tri-synchro regulator, which sits in place of a traditional escapement.
“Spring Drive combines the best of mechanical watchmaking and the best of quartz timekeeping to create a state of the art caliber that lacks the weaknesses inherent to both of these movements.”
Here’s how the Tri-synchro regulator works. At the end of the gear train is a small disc called the glide wheel. With the help of two electromagnets, the glide wheel slows down the release of energy from the mainspring, and it does so without friction because it doesn’t start and stop in the way a traditional mechanical escapement does. And because it’s constantly turning, Spring Drive watches have a really unique feature —a seconds hand that advances in a smooth, continuous motion across the dial.
But the above doesn’t account for the rate at which that energy is released, so how does the Tri-synchro regulator do that?
As it spins, the glide wheel creates an electrical current, and this current runs through and activates an integrated circuit and a quartz oscillator.
Quartz crystals are piezoelectric, which means that if you apply electricity to a piece of quartz cut into the right shape — in the case of the movement here that shape is a tuning fork — then it will vibrate at a precise frequency. To be specific, the frequency is 32,768 oscillations-per-second. To get these quartz crystals vibrating, Spring Drive watches make use of the aforementioned electrical current produced through the glide wheel.
The frequency produced by a quartz oscillator functions as a reference signal for the integrated circuit, which compares that signal to the revolution speed of the glide wheel. This is where the regulation happens. If it senses that the glide wheel is running too fast, the integrated circuit applies an electromagnetic break to the wheel, which slows it down. Essentially, the integrated circuit is a sort of on/off switch for this electromagnetic brake.
Now thoroughly regulated, Spring Drive movements are capable of a whopping +/-1 second a day. And because the integrated circuit consumes very little power, about 1/300 millionth of the power consumed by a typical LED light bulb, Spring Drive movements are able to maintain an impressive power reserve of 72 hours.
Performance aside, Spring Drive movements are extremely beautiful, with a host of high-end finishes that make that open case back all the more worthwhile. And at first glance, they even look like classic mechanical movements. Of course, they look the way they do because many of the mechanics are still there, which is why, for those partial to mechanical movements, Spring Drive holds such high appeal.
Movements and watches featured are instructional samples. No Grand Seiko watches or movements were hurt in the making of this series.