Grand Seiko 9SA5 - the Dual-Impulse Escapement explained
Grand Seiko is known for the particularly good finish of its watches. However, when looking at the back of the watches, one notices that the finish of the movements is not executed with the same passion as that of the dial and case.
Not so with the 9SA5.
The attention to detail is immediately apparent here. This movement not only stands out visually, it is also technically convincing across the board.
With the Dual-Impulse Escapement, Grand Seiko proves that it is one of the top watch manufacturers par excellence. The Dual-Impulse Escapement is an innovation that makes the movement not only light, but also about 30% more efficient.
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Grand Seiko's Dual-Impulse Escapement - the innovation explained
When people in the watch world talk about innovations, they often puff up small improvements that optimize an existing movement.
However, the Dual-Impulse Escapement lives up to the hype because it replaces the anchor movement, the most important part of the watch.
To understand how the Dual-Impulse Escapement works, we first need to understand how a mechanical watch movement works at all. Fortunately, we have already written an in-depth blog post about mechanical watch movements that explains everything in detail.
In short, in mechanical movements, the energy of the mainspring is released in a controlled manner. The palletfork locks and unlocks the escape wheel. The whole thing is controlled by the balance or flywheel, which oscillates back and forth. The time the balance needs for a pendulum movement is always the same. This is how time is measured.
For illustration we recommend the following video:
YouTube: SWISS LEVER ESCAPEMENT
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To keep the balance turning, an impulse must be transmitted from the escape wheel (which is under the tension of the main spring) to the balance-wheel after each oscillation.
In a conventional lever Escapement, this is done via the friction of the escape wheel on the oblique tooth of the pallet lever as follows:
Legend: 1) Turning direction of the escape wheel, 2) Friction between the ruby and the tooth of the escape wheel, 3) Resulting force pulse transmitted to the balance.
So, on a Swiss Lever Escapement, the ruby on the escapement has 2 functions: one is to lock and unlock the escape wheel, and the other is to transmit an impulse to the balance.
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The Grand Seiko Dual Impulse Escapement
The starting position
The escape wheel is locked by the anchor with the top ruby and the flywheel, which is fixed just below the balance roller, first swings counterclockwise before turning back clockwise.
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Position 2
In this position, the flywheel and thus the balance roller rotates clockwise. The semi-circular "Impulse Pin" located on the Balance Roller is used to release the anchor. Releasing the anchor causes the anchor wheel to rotate until it contacts the "Roller Pallet" (the ruby tooth on the Balance Roller) and gives a direct impulse to the flywheel.
This is precisely where the innovation of Grand Seiko's Dual-Impulse Escapement comes in. Unlike the Swiss Lever Escapement, the impulse is not transmitted through the anchor but directly to the balance wheel, which is much more energy-efficient.
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Position 3
After the escape wheel has transmitted the direct impulse to the flywheel, it stopps at the lower ruby until the flywheel swings back again.
By the way, here on this picture the flywheel is just at the turning point of the clockwise movement before it turns back again counterclockwise.
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Position 4
When the flywheel swings back counterclockwise, the anchor is released again. The grinding of the escape wheel on the lower ruby transmits an indirect impulse to the flywheel. The principle with this impulse is similar to a conventional lever movement (Swiss Lever). In this arrangement, however, the angles are somewhat more advantageous, resulting in less friction.
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Position 5
The moment the "impulse pin" slips out of the anchor, the Anchor is again in contact with the banking pin and thus locks the escape wheel with the upper ruby.
And then the whole motion sequence starts again - due to the high swing rate of 36,000 beats a whole 5 times per second!
I hope you were able to follow our explanation and now understand how Dual-Impulse Escapement works.
For better visualization, feel free to check out this 3D animation.
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What are the advantages of dual-impulse escapement?
The Grand Seiko Dual-Impulse Escapement offers two main advantages. Firstly, the movement is highly efficient due to the low friction and direct impulse. In combination with some other small improvements, the 9SA5 is 30% more efficient than comparable high-beat movements from Grand Seiko. The additional efficiency has a positive impact on the power reserve, which generally has relatively low performance in high-beat movements.
Since the pallet lever movement is particularly low-friction, service intervals can additionally be extended. The need for frequent maintenance is normally another disadvantage of high-beat movements. With this movement, the service intervals are comparable to movements running at a "normal frequency".
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What is a high-beat movement? And what disadvantages does it have?
Grand Seiko is particularly known for its Spring Drive movement and its High-Beat movements.
A high-beat movement beats at a higher frequency than a normal movement. This means that the balance oscillates back and forth 5 times per second instead of 4 times, which is standard in the luxury watch world.
This in turn means that the entire sequence of movements, as we described earlier with the pictures of the pallet lever movement, runs 5 times per second. In product descriptions, the half oscillations of the balance per hour are usually mentioned. For the Grand Seiko High Beat movements, this is 36,000 vibrations per hour.
High-beat movements are particularly accurate, because after shocks the balance recovers more quickly and oscillates again at the exact frequency. They are therefore more frequency-stable, which results in more accurate timekeeping.
Of course, the increased frequency also has some disadvantages. One would be the increased energy consumption of high-beat movements, and the other would be faster wear.
As previously mentioned, dual-impulse escapement is so efficient and low-friction that these two disadvantages become insignificant.
For a detailed explanation of all the pros and cons of high-beat movements, feel free to read our blog article about Grand Seiko's high-beat movements.
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Other small innovations of the 9SA5
The new lever movement is the biggest innovation, but the 9SA5 also impresses with some minor improvements that add up to make a difference in the performance and dimensions of the finished movement.
Manufacturing with MEMS technology
You may have noticed that both the pallet and escape wheel of the new pallet lever movement have small cutouts.
Both are in fact produced using MEMS (Micro-Electro-Mechanical Systems). This is a process that can be used to produce extremely light and extremely precise parts that have a manufacturing tolerance of one thousandth of a millimeter.
Parts optimized with MEMS are on average 5% lighter, which is important because they require less energy to rotate, which in turn extends the power reserve.
In other words, so that the movement can be even lighter, even the tiniest parts were skeletonized.
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Better lubrication due to tooth profile on escape wheel
The new pallet lever movement alone is not enough to extend the service intervals of high-beat movements, which are shortened by the high beat rate, to a normal duration.
In addition, a new tooth profile was therefore developed that saves lubricant.
Normally, gears are provided with a rounding. The gear of the 9SA5, on the other hand, has a step in which lubricant is collected for longer.
Normally, the edge of a gear is rounded. The lubricant (orange here) then runs down the rounding.
The step on the escape wheel of the 9SA5 provides much more space for the lubricant, ensuring long-term lubrication.
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Polished gears
A mere profile optimization would of course be too little for a global brand like Grand Seiko. Therefore, no effort was spared in the surface finish either.
The teeth are all polished by hand. This is not done for visual reasons alone, but rather for efficiency. The smoother the surface of the teeth, the lower the friction during operation, which both reduces wear and increases efficiency.
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Twin Barrels/Double barrel
To enable the excellent 80-hour power reserve, Grand Seiko had to install a double barrel in addition to the more efficient lever movement. In it, 2 mainsprings are connected in series to store even more energy and thus extend the power reserve.
Date change mechanism
A new mechanism was developed to change the date more quickly. Even though this is not a daily used function for many watch owners, it once again shows Grand Seiko's attention to detail. It also shows that Grand Seiko has invested all its resources in this new movement and nothing has been spared.
The date change feature is a charming detail!
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Free-Sprung Balance Regulator
In order to adjust the speed of the balance or flywheel, a mechanism is needed that usually preloads or releases the spring a little.
The better variant, however, is a so-called "Free-Sprung Balance Regulator", which is only used in the most expensive and best movements.
In the Free-Sprung Balance Regulator, the moment of inertia and thus the speed of the balance is adjusted using 4 adjusting screws. If the screws are all turned towards the center, the balance turns faster; if they are turned outwards, the balance turns slower.
The principle is the same as spinning in a circle on an office chair with your arms outstretched: with your arms tightened, you spin faster.
The advantages of the Free-Sprung Balance Regulator are, on the one hand, that the moment of inertia and thus the speed of the balance can be adjusted even more precisely. Since there is no need for a regulating mechanism that pulls on the hairspring, the life of the hairspring is extended.
Thus, the movement becomes more durable and remains accurate longer.
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Key data of the 9SA5 movement
- Automatic movement with manual winding
- Accuracy in the laboratory: +5 to -3 seconds per day
- Accuracy in everyday life: +8 to -1 second per day
- Power reserve: 80 hours
- Half-oscillation rate: 36,000 half-oscillations per hour (high-beat)
- 47 rubies
- Functions: Dual-impulse escapement, double barrel, instantaneous date change mechanism
| Winding | Automatic movement with manual winding |
| Average daily rate | +5 to -3 seconds per day |
| Accuracy during normal use | +8 to -1 second per day |
| Power Reserve | 80 Hours |
| Half swing rate | 36,000 vibrations per hour (high-beat) |
| Number of jewels | 47 rubies |
| Functions | -Dual-Impulse Escapement -Double barrel -Instant date change. |
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Conclusion - buy or stay away from it?
You may have noticed while reading that our opinion on this movement is not 100% objective.
During our extensive research, we did fall a little in love with this movement. It is not only a masterpiece in technical terms, but also visually an eye-catcher!
But would we recommend this movement to anyone? Absolutely not!
We would recommend this movement to you if, like us, you have an interest in the engineering and craftsmanship that goes into this movement.
Because you also have to invest quite a bit to be able to call this movement your own. On the one hand, you have to spend more money than if you were to buy a comparable watch. On the other hand, you have to expect to have your watch serviced at least every 5 years, which causes additional costs.
We wouldn't recommend this movement to you if you don't really care about the technology behind the watch and just want the most accurate movement possible. In this case, we suggest you consider a watch with a Spring Drive movement or even a quartz movement.
Source cover photo: Grand Seiko
About the author
Maio Rosatzin
My passion began with a Breitling Premier B01. Since then, I've been sharing my fascination for watchmaking here on my blog. Let's dive into this fascinating world together!
