Spring Drive is a name given to a series of watch movements produced by

Epson Seiko Epson Corporation, or simply known as Epson, is a Japanese multinational electronics company and one of the world's largest manufacturers of computer printers and information- and imaging-related equipment. Headquartered in Suwa, Nagano ...

in Shiojiri. The concept of using a mainspring to power a quartz timing package was first conceived in 1977 by Yoshikazu Akahane (赤羽好和) at Suwa Seikosha (now a part of Seiko Epson after a 1985 merger). Specified to one second accuracy per day, the movement uses a conventional gear train as in traditional mechanical watches, but rather than an

escapement An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy ...

and

balance wheel A balance wheel, or balance, is the timekeeping device used in mechanical watches and small clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a ...

, instead features Seiko's ''Tri-synchro Regulator'' system in which power delivery to the watch hands is regulated based on a reference quartz signal. Commercially released in 1999, the movement is found in watches distributed by the Seiko Watch Corporation, including its Credor, Grand Seiko, Presage, and Prospex brands.

Mechanics

The Spring Drive uses a conventional mainspring and

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...

along with automatic and/or stem winding to store energy, just as in a mechanical watch. However, the

and

in mechanical watches is replaced by Seiko's ''Tri-synchro Regulator'' system, a

phase-locked loop A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a ...

wherein a rotor, which Seiko refers to as a "glide wheel", is powered by the mainspring barrel via a

stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric m ...

. The glide wheel in turn powers a reference quartz crystal and accompanying

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

which controls an electromagnetic brake which then regulates the rotational speed of the glide wheel itself. The glide wheel is intended to rotate eight times per second; the rotational speed is sampled once every rotation and a variable braking force is continuously applied to maintain that target frequency. As the glide wheel directly powers the seconds hand of the watch, this results in a true continuously sweeping second hand – in contrast to the beats per time motion resulting from the back-and-forth movement of traditional mechanical watches or the tick of typical quartz watches. The movement is specified to ±15 seconds per month.

History

The design was first conceived by Yoshikazu Akahane at Suwa Seikosha in 1977 and

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

s were applied for it in 1982; in total, no fewer than 230 patents have been applied worldwide for this movement. Initial development was hindered by the high energy consumption of the reference quartz crystal and integrated circuit making a watch with a then-target 48-hour power reserve impossible; another attempt in 1993 was also unsuccessful for the same reason. It was not until a third attempt in 1997, using a quartz crystal and integrated circuit with energy consumption approximately one one-hundredth that used in the initial attempt in 1982 that a Spring Drive watch with sufficient power reserve was deemed feasible. Over 600 prototypes were produced during development. The Spring Drive movement was announced publicly in 1997 and presented at the 1998 Basel Watch Fair. In 1999, the first production models were made available in Japan as limited edition, manual-wind watches in both the Credor and Seiko brands. The first non-limited model was released in Japan in 2002. The 1st spring drive automatic-wind movement of Grand Seiko was released in September, 2004, the reference number is SBGA001. The first automatic-wind Spring Drive model was released in 2005 and coincided with the introduction of the Spring Drive movement to markets outside of Japan.

Calibers

Early models, manual wind and 48h power reserve: * 7R68 : 30 jewels, date. * 7R78 : 30 jewels, date. * 7R88 : 30 jewels, date. * 7R99 : 32 jewels. Current

calibers In guns, particularly firearms, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore match ...

with standard features. Time accuracy: monthly rate within ±15 sec (equivalent to a daily rate of ±1 sec) and power reserve (72h) indicator. * 5R64 : 32 jewels, date, small seconds hand. * 5R65 : 30 jewels, date. * 5R66 : 30 jewels, date, GMT. * 5R67 : 30 jewels, Moon Phase indicator. * 5R77 : 30 jewels, Moon Phase indicator. * 5R85 : 49 jewels, date, Chronograph, Izul. * 5R86 : 50 jewels, date, GMT, Chronograph, Spacewalk. * 7R06 : 88 jewels, manual winding, Sonnerie. * 7R08 : 44 jewels, manual winding, Eichi I. * 7R11 : 112 jewels, manual winding, Minute Repeater. * 7R14 : 41 jewels, manual winding, Eichi II. * 9R01 : 56 jewels, manual winding. * 9R15 : 30 jewels, date. Monthly rate within ±10 sec (±0.5 sec per day). * 9R31 : 30 jewels, manual wind * 9R65 : 30 jewels, date. * 9R66 : 30 jewels, date, GMT. * 9R84 : 41 jewels, date, Chronograph. * 9R86 : 50 jewels, date, GMT, Chronograph. * 9R96 : 50 jewels, date, GMT, Chronograph. Current calibers with higher power reserve and higher accuracy. Time accuracy: monthly rate within ±10 sec (equivalent to a daily rate of ±0.5 sec) and power reserve (5 days) indicator. * 9RA5 : 38 jewels, date. * 9RA2 : 38 jewels, date. Rear power reserve indicator.

Notes and references

{{Seiko Watches Epson Seiko Timekeeping components Japanese inventions de:Seiko#Spring Drive