Style / World of Watches (WOW)

A Look Into a Watch’s Direct Dual Impulse System

Moving beyond the standard Swiss lever system, we move straight into the new Grand Seiko system of regulating organs in part five of our continuing series exploring what makes time tick.

Sep 23, 2021 | By Ashok Soman
George Daniel the Space Traveller
Pocket watch from George Daniel, the Space Traveller. Image: George Daniel

The heart of watchmaking is not about measuring vibrations, mechanical or otherwise. It is about people, and here we are not just referring to watchmakers. Yes, the thing people love most about a Breguet pocket watch is that he made his watches himself, in the sense that he was not just a brand name. Obviously, this was when the man himself was living and working in Paris. He wanted to make better watches than what he saw around him, and he did. This is not a feature of the past, and speaks directly to the development of new escapements, and experiments in this area.

Welcome back to our continuing series on the regulating organs of the mechanical watch, which has been disrupted for a few issues due to a shortage of pages in the magazine. Having covered the main components of the typical heart of the mechanical wristwatch, we are now in more esoteric territory. In this fifth installment of this series, we are looking at something new, which is the escapement of the calibre 9SA5 from Grand Seiko. This is a direct dual impulse system so we will also reference a related system, the Omega Co-Axial escapement and George Daniels’ invention of said system. We will turn back to both this and the direct impulse system of Ulysse Nardin in an upcoming article.

Returning for a moment to the footing we got off on, with regards to pioneering watchmakers such as Abraham-Louis Breguet and others of his ilk, these days, we tend to have the same feelings for the likes of Philippe Dufour, Stefan Kudoke and Kari Voutilainen. There are also creators such as Max Busser of MB&F and Richard Mille, who are not watchmakers but really charismatic industry insiders. Where Breguet, Ferdinand Berthoud, John Harrison and Thomas Mudge all worked on their own solutions for a better timekeeper, these days such work is more likely to be done at the offices of the Swatch Group, Rolex and Patek Philippe, or Audemars Piguet Renaud et Papi, Greubel- Forsey and Christoph Claret.

The price of research and development

Grand Seiko SLGH007
Grand Seiko SLGH007 is one of two models this year powered by calibre 9SA5. Image: Grand Seiko

There are technical reasons for this, but the story has long progressed past that point. For most of us, the meaning of time is defined by the marketers who hold the reigns of the top watch brands. Whatever generates timekeeping results on your wrist is a result of a business decision based on what can sell for the best possible price while delivering the best possible value.

This brings us back to Grand Seiko, which already has excellent movements with the traditional Swiss lever system and the mechanical-quartz hybrid known as Spring Drive. Seeing yet another escapement option here serves to remind the world that some brands really are investing in refining the mechanical timekeeping system further. Let us then try to understand the value proposition here.

Here is how Grand Seiko describes it: The Dual Impulse Escapement is a unique mechanism which combines “direct impulse,” where power is transferred directly from the escape wheel to the balance, with conventional “indirect impulse.” Thereby, it transfers power to the balance through the mainspring with increased efficiency. Conventional wisdom decrees the more you increase the vibration rate of the balance, the lower the power transfer efficiency. This is because the escape wheel and pallet fork cannot keep up with the high oscillation speed. This challenge is met in Caliber 9SA5 as it has new components made with MEMS technology to increase the escapement efficiency. Connecting these to the twin barrels allows for 10 beats per second while delivering a continuous operation period of 80 hours.

There is quite a lot to unpack in that statement from Grand Seiko but fortunately, they spent a good bit of time explaining it for specialists. One handicap facing specialists like us for the moment is that there is no independent watchmaking analysis for the new escapement. This means that we have to extrapolate from our theoretical understanding of watchmaking principles (not being watchmakers nor mechanical engineers ourselves), while taking the manufacturer’s word at face value.

Revising the Swiss lever

In terms of mechanical clockwork, the Swiss lever system is the dominant narrative, but it is just one version of the same tale. Raw kinetic energy stored in the mainspring winds its way through the gear train to be transformed by the regulating organs into regular pulses that turn the motion works, which tell the hour, minute and second hands when to move.

Here is a slightly more detailed summary of how it works. The escape wheel interacts with the balance via the pallet fork, but it also connects with the gear train. The escape wheel receives unregulated energy from the mainspring via the gear train, and transmits it to the balance wheel and balance spring. The balance wheel and spring get a push, which is called an impulse. In return, the balance wheel and spring send regulated energy to the escape wheel via the pallet fork.

A rundown of the regulating organs

Swiss lever escapement from Patek Philippe
Components of a Swiss lever escapement. Image: Patek Philippe

Balance spring: Fine helical conventionally-flat-but-sometimes-with-overcoil spring set on the balance wheel. Made of an alloy, or silicon. Sometimes known as the hairspring.

Balance wheel: Ring in an alloy that surrounds the balance spring.

Escape wheel: Steel or silicon wheel that transmits and receives energy from the balance wheel.

Pallet fork: Steel lever with jewel end stones resembling a two-pronged fork. Sometimes in silicon, without jewels.

Essential requirements of the watch escapement

  • Impulse to the oscillator at both vibrations of each oscillation.
  • Impulse delivered tangentially with minimum friction.
  • After impulse the oscillator is to be free to complete the vibration without further contact with the escapement.
  • The oscillator to be self-starting while winding the mainspring from the run-down condition.
  • The oscillator to restart after being accidentally stopped.

Variations on a theme

Grand Seiko SLGH005
Grand Seiko SLGH005 and calibre 9SA5. Image: Grand Seiko

To begin with, the new Grand Seiko regulating organs are a sort of variation on the lever system — a hybrid if you will. For ease of reference we will simply refer to this as a kind of lever escapement, because it is. It is also different, because of that direct impulse that is without the pallet fork. For the power to reach the balance assembly now, the escape wheel will have to move it directly. Likewise, the escape wheel will get locked into a steady beat by the balance directly. We can thus call this a direct system. Bringing the pallet fork back into the picture, we can see how this is an indirect system, by way of comparison. Seems easy enough to follow so far.

A few things immediately stand out in Grand Seiko’s new Dual Impulse Escapement, mainly the shape of the escape wheel and the lever. That lever in particular may remind you of the Omega Co-Axial system, or at least of the George Daniels co-axial escapement. Indeed, the lever shows you just how the escape wheel delivers a direct impulse to the balance, while receiving an indirect impulse from the lever. The end farthest from the balance is indirect while the end closest to the balance is direct, at a point analogous to the roller pin of the balance. Given that the escape wheel turns clockwise, we can surmise that energy is delivered to the roller pin, thus impulsing the balance and returning energy via the pallet fork.

The angles of contact are key here, defining how much friction is in play, and so is the unusual layout of the lever, relative to the escape wheel; the shape of this wheel also plays an important role, no doubt. We know most of this from the example of the co-axial system, and also from the architecture of Rolex and Patek Philippe’s proprietary lever designs and wheel shapes. Like those systems, this one was also built with special technology to make and shape parts that are extraordinarily precise, light and strong. Grand Seiko calls this MEMS, and it is a lithographic system. Practically speaking, the net upside of Grand Seiko’s new regulating system is a gain of 30 hours in terms of power reserve over the 9S movement, which is relatively conventional.

We end this foray into the regulating organs of calibre 9SA5 with a brief note about the balance spring, which now features an overcoil where the 9S was flat. The publicity team was very proud of this overcoil, and we do sympathise with their valiant efforts to keep the public interested in these kinds of details. It is useful to once again consider the example of Omega here, when it launched its co-axial escapement. In those days, the movement was an ordinary ETA calibre that had been modified to take the larger and more complex co-axial regulating organs. Convincing customers that Omega now had a better watch was no easy matter. In that case, it was the eventual extension of the warranty that made the difference — the new regulating organs made lubrication less important (theoretically perhaps unnecessary even), and wear-and-tear was less of an issue. We expect to hear something similar from Grand Seiko in the years to come.

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