Grand Seiko Spring Drive 5DaysMarch 3, 2023
News from the house Grand Seiko today, starts off with the announcement of the brand new Grand Seiko Springe Drive movement, the 9RA2 which was developed based on the 2020 launched, 9RA5.
To quickly recap, the Grand Seiko’s Spring Drive movements essentially consist of a classical gear train, except that the balance wheel on these are replaced with a “glide wheel” that acts like the fixed fourth wheel of the movement and drives the seconds hand. The regulation of the gear train maintained by an electromagnet, which brakes the motion of the wheel to keep it constant. The system delivers 256 brakes per second, controlled by a samadium-cobalt electromagnet with 25,000 coils.
The winding system on Grand Seiko Springe Drive movements are bi-directional and controlled by a lever that was developed in-house by Seiko in 1959. Last year, for the 9RA5 movement, the Magic Lever, as it is known, was made off-set from its old placement at the centre of the movement, which allowed Grand Seiko’s watchmakers to vastly slim the calibre down. Two barrels power the movement, in differing sizes, and run in overlapping series so as to deliver a very even torque throughout the movement’s power reserve, while lasting for 120 hours.
In addition, a single piece bridge was developed and machined for the 9RA2, which is meant to secure the new layout of the gear train, under one solid structure with significant shock resistance improvements. On the back of the movement, in fact, you can just make out the two distinct barrels above the crown stem.
The 9RA5 movement was also more precise thanks to an improved integrated circuit that has a sensor to monitor the temperature of the movement. Since quartz, which is the oscillating stone that vibrates to deliver the regulating function of the electromechanical brake, is temperature sensitive, the circuit board compensates for any fluctuations in the oscillation rate. The self-winding Grand Seiko Springe Drive 5 Days Caliber 9RA2 builds on the achievements of the 9RA5 with its own set of innovations, starting with a slimming down of all movement parts and a design adjustment that reduces the distance from the bottom of the movement to the center of it crown by about 0.8mm. Grand Seiko also states that the crown is as well moved as far back as possible, which allows for the center of gravity on the movement to be lowered, resulting in a “comfortable and natural fit”. Next, the 9RA2 uses a redesigned Magic Lever with crank wheel assembly that is offset from the central pinion, which allows adds to the movement’s slimness. An additional benefit of this new position simultaneously adds to the movement’s winding efficiency. Third, the 9RA2 has two barrels in series that are each of different sizes, to make the most of the small real-estate on the movement, most efficiently. Grand Seiko admits that while the two different sized barrels present a challenge where they’re likely to experience fluctuations in the transmission efficiency of energy, improvements were made to the barrels themselves to ensure that energy transmission pertaining to each mainspring holds to the same efficiency, regardless of barrel size. Winding and unwinding rates for the overall movement are therefore kept steady. Lastly, we see that the entire going train is kept under the wraps of a single solid bridge that accounts for significantly better strength, durability and shock resistance. Incorporated onto the bridge is also a power reserve indicator. Of course, given that this is Grand Seiko, the 9RA2’s bridge and rotor has a frosting finish, inspired by the “gentle frost that covers the trees in the early winter” at the movement’s birthplace, Shinshu Nagano Prefecture. There’s also the bevels on the movement and its screws which are finished with cut diamonds that represent the brilliance of the stars of the night sky, at the same location.