In-Depth: Does Spring Drive Have An Escapement?
Of mainsprings and Tri-synchro regulators.
Originally published by Jack Forster on HODINKEE, October 2nd 2020
Not too many moons ago, we took a brief look at some of the most commonly used escapements in mechanical watches. (I actually, and characteristically, went on a bit in that story, but given how much more could have been said on the subject, it felt brief to me!) One of the comments, from H. Community Member Chronos2, raised an interesting point, which was that I had not discussed Spring Drive at all. I had indeed not, having chosen to focus on Grand Seiko’s new Hi-Beat escapement, but the more I thought about the observation, the more I thought I might indeed have missed something – and also, the more I wondered, based on a precise definition of an escapement, if you could consider the Spring Drive to have one.
More specifically, I wondered about the Tri-synchro regulator, as Seiko calls it – this is the group of components which actually function as the regulating system in any and all Spring Drive watches. It had seemed fairly cut-and-dried to me to exclude Spring Drive from a discussion of modern escapements – which, after all, are generally thought of as mechanical devices – but the more I thought about it, the less black-and-white the question seemed.
The escapement, in a mechanical watch or clock, takes the one-way rotational movement of the wheels of the going train, and uses it to power the back-and-forth, two-way movement of an oscillator. The oscillator is, almost invariably, a balance wheel or pendulum (with some exotic exceptions). An essential part of most mechanical escapements is the escape wheel, which has specially shaped teeth designed to interact with some component (the lever, in a lever watch) which releases one tooth of the escape wheel every time the oscillator swings. The tooth “escapes,” and the escape wheel rotates. As it does so, it pushes on the lever (in a lever watch) which in turn gives the balance wheel a push, just like someone pushing a child on a swing. As you can see, the basic characteristics of a mechanical escapement are that it both provides energy from the going train to the balance, while at the same time controlling the rate at which the train wheels rotate, all the way back to the mainspring barrel.
Now, among the several interesting things about Spring Drive is the fact that the power source is not a battery or capacitor; rather, it is the mainspring. This is in sharp contrast to pretty much every other watch with a quartz tuning fork oscillator, in which the battery supplies the juice necessary to keep the quartz oscillator vibrating back and forth (generally at a frequency of 32,768 Hz).
The crystal vibrates because quartz is what’s called a piezoelectric material – that is, it changes shape when an electrical current is applied. In a conventional quartz watch, it’s a replaceable battery – this can be kept topped up by a solar cell, as in Citizen’s Eco-Drive watches, or the Tough Solar G-Shocks (everyone’s favorite watch to have if you fall through a one-way wormhole and end up with nothing but your watch, a Swiss army knife, and your trusty Zippo, back in the time of the dinosaurs). Another way of keeping the battery charged is used by the Seiko Kinetic watches. Here, there is a rotor just like the one you’d find in an automatic watch, except instead of winding a mainspring, it’s connected to gears that turn a miniature electrical generator; the current supplied is used to keep the battery from running too far down.
Spring Drive, on the other hand, uses a standard watch mainspring to generate power. The mainspring may be kept wound by an automatic winding system – Grand Seiko uses a variation in its Spring Drive watches of the classic Magic Lever automatic winding system, which the company first introduced in 1959 – or it can be hand-wound, as is the case in the Grand Seiko 8-Day watches (as well as, of course, the fan-favorite Credor Eichi timepieces). In either case, the gear train of a Spring Drive watch from the mainspring barrel, all the way down the line to where you would find an escape wheel in a mechanical watch, is entirely mechanical. The exact gear ratios, number of gears, and other specifics are different from a standard mechanical watch, but the basic principle of wheels engaging with pinions, with torque decreasing and rotational speed increasing as you progress towards the regulating organs, is the same in both Spring Drive and a completely mechanical watch with a mechanical escapement.
At the point where, in a mechanical watch, you would find the escape wheel, lever, and balance, you find instead in a Spring Drive watch what Seiko calls the Tri-synchro regulator, which performs the same function in a Spring Drive movement that’s performed by the escapement and balance in a mechanical watch. The Tri-synchro regulator consists of a small wheel which rotates in between the jaws of two wire-wrapped components, generating electricity, as well as an integrated circuit and a quartz timing module.
The first Spring Drive prototype was completed in 1982, and the first production Spring Drive wasn’t released until 1999 – the development process focused very much on the challenges involved in both miniaturizing the system and reducing the amount of electrical energy consumed by the IC and quartz oscillator, as well as maximizing the amount of energy produced by the Tri-synchro regulator. In the 1982 prototype, what would become the glide wheel is visible on the left, rotating over three quite large stationary elements. In an electrical generator, the rotating element is called a rotor and the static element, the stator; the glide wheel acts as a rotor and the wire-wound elements act as the stator.
Electrical energy flows from the generator system to the integrated circuit and quartz crystal. The crystal vibrates at 32,768 Hz, which produces a time reference signal. This signal is checked by IC against the speed of rotation of the glide wheel, and if necessary, an electromagnetic field is generated to brake the motion of the glide wheel and hold its rotational speed to exactly eight revolutions per second.
The Tri-synchro regulator itself consists of the glide wheel, coil-wound stators, and the IC and quartz oscillator that constitute the actual regulating system. In a Spring Drive movement, the glide wheel, stators, and IC fulfill the functions of the escape wheel and lever in a conventional mechanical watch, while the role of the balance wheel is fulfilled by the quartz crystal.
Now, if we ask ourselves, “does Spring Drive contain an escapement,” we can turn to the various definitions of “escapement” out there. It’s worth noting at this point that pretty much every dictionary definition of the word which is related to horology (there are non-horological uses of the word – the device in a mechanical typewriter which advances the carriage automatically when a key is pressed and released is also called an escapement, for instance) assumes that escapements are mechanical rather than, potentially, electromechanical devices as well. However, the basic functionality of an escapement is captured very well, I think, by the Oxford English Dictionary, which says an escapement is, “A mechanism in a clock or watch that alternately checks and releases the train by a fixed amount and transmits a periodic impulse from the spring or weight to the balance wheel or pendulum.”
On this score, I think you can certainly make an argument that the Tri-synchro regulator is an escapement – an oscillator and escapement since it includes the quartz crystal. It certainly fulfills the definition of an escapement from a function perspective – it provides motive power to the oscillator (via an electrical current), and it also controls the going train, albeit not in fixed amounts, but rather through a continuous braking process, which gives the Spring Drive watches their characteristic, smoothly gliding seconds hand (and smoothly gliding hour and minute hands as well, as the hour and minute hands are driven, as is the seconds hand, by gears of the going train, rather than by stepper motors, as in a conventional quartz watch).
One interesting point, which was raised by Chronos2, is that there is no electrical storage system in Spring Drive watches. The power source is purely mechanical, and if the mainspring winds down, the watch will stop immediately as there is no battery or capacitor and, indeed, nothing for them to drive, even if they were present in the movement.
A final question is whether or not a conventional quartz watch has an escapement in the sense we have been discussing them. I would say no, at least on initial consideration. A quartz watch has a battery that drives an oscillator, but the mechanism that drives the oscillator does not have a rate of “unwinding,” so to speak, that corresponds to the mechanical train in Spring Drive or a mechanical watch. Instead, the IC in a standard quartz watch counts the number of oscillations of the crystal, and when an equivalent to one second is reached, it sends a signal to the stepper motor to advance the second hand. If the motion of the seconds hand were determined by the rate of depletion of the battery, we would have a much closer analogy to a true mechanical (or electro-mechanical) escapement, but this is not the case.
There are a number of respects in which Spring Drive is unique in comparison to other quartz-controlled wristwatches, but to me, this is one of the most significant, and it seems to me that it makes Spring Drive a closer relative to standard mechanical watches than one might think. However, as is always the case with Spring Drive, I think ultimately it’s best understood as its own thing – a timekeeping and regulating system with no really close relative anywhere else in horology. Hope you have enjoyed this little thought experiment and, as always, I look forward to, and even hope to be, violently disagreed with in the comments!