Spring Drive
The Spring Drive is a novel watch movement that was developed by Seiko Epson.
It uses a mainspring, barrel, automatic winder and stem winding like in a mechanical watch to store the watch energy. The conventional escapement is replaced with a device that Seiko calls a Tri-synchro Regulator to regulate the unwinding of the mainspring. The regulator controls the use of the three forms of energy used in the Spring Drive mechanism; the mechanical power of the mainspring, the electrical energy generated from this mechanical power, and the electromagnetic energy that governs the rotation of the glide wheel. The energy produced by the glide wheel is used to power a control circuit and quartz crystal oscillator, which in turn regulates the electro-mechanical braking of the glide wheel.
The glide wheel's speed is sampled 8 times per second (i.e. each time it makes a complete revolution around the regulator) and compared with the reference quartz signal by the circuit. A variable braking force is continuously applied to regulate the glide wheel's frequency. This is the only movement with a time-only feedback (or phase-locked) loop in existence today.
The Tri-synchro Regulator's innovations result in a watch where the hands glide instead of ticking as in a conventional mechanical or quartz watch. This is because the movement never stops as in a traditional escapement, it is slowed to the proper speed by the brake. The movement is spec-ed to 1 second accuracy per day. However, 1-2s per week is commonly reported by owners.
The movement is used on the Spring Drive International collection and in some watches of Grand Seiko, CREDOR, GALANTE, IZUL and PROSPEX series. Complications include moon phase, power reserve, chronograph, sonnerie, GMT and calendar functions. These watches are fairly expensive, with the least complicated models costing several thousand dollars. The top of the line Credor Sonnerie in Rose Gold is over $150,000 and can be considered a grande complication.
History
The design was first conceived in 1977, and patents were applied for in 1982. The movement was announced publicly in 1997, presented at the 1998 Basel Watch Fair and first appeared commercially in the Credor 'luxury watch' range as a limited edition in 1999. A version which included an automatic winder was shown in Seiko models at the 2005 Basel Watch Fair. The internationally available Seiko models were officially launched at the Musée d'Orsay in Paris on September 14, and went on sale the following day.
Swatch's research company ASULAB has developed a conceptually similar movement called the High Precision Mechanics calibre. [1]. Several proof of concept prototypes based on the ETA 2824 calibre were produced in the late 1990's.
Seiko's efforts with the Spring Drive predates ASULAB's HPM, since Spring Drive watches were already on sale in 1999.
Spring Drive In Numbers
- 0.025 mm. The thickness of each layer of alloy in the coil block.
- 1 second a day accuracy, 10 times better than the chronometer mechanical standard.
- 3 types of energy are controlled by the Tri-synchro regulator: mechanical, electrical and electro-magnetic.
- 5 craftsmen and women. Only Seiko’s 5 most skilled craftsmen and women were entrusted with the assembly of Spring Drive initially. [This number is probably exceeded today]
- 8 times per second. The precise speed at which the glide wheel turns within the electro-magnetic braking system.
- 13 generations of prototype were built in the development phases.
- 15 microns. The width of the wire in the Tri-synchro regulator’s coil.
- 18 layers of amorphous alloy in the coil block.
- 25 nanowatts. The minute amount of power needed to activate the regulator, less than half that needed in all other watch circuits.
- 28 years of research and development invested in the project.
- 30 percent improvement in winding efficiency achieved through the improved Magic Lever system.
- 30 jewels in the movement. 32 in the small second hand version.
- 72 hours of power reserve.
- 88 jewels in the 7R06 Sonnerie movement.
- 92 years since Seiko built its first wristwatch.
- 124 years of Seiko's expertise in time keeping.
- 230 patents have been applied for in Japan, USA and the EU.
- 276 components in the movement. 280 in the small second hand version.
- 600 actual prototypes were built between 1997 and 2004.
- 25,000 The number of times the coil is wound, for maximum energy efficiency.
- 28,800 The number of times the glide wheel turns per hour.
Calibers
- 5R64 : 32 stones, day, small seconds hand.
- 5R65 : 30 stones, day.
- 5R66 : 30 stones, day, GMT.
- 5R67 : 30 stones, Moon Phase indicator.
- 5R77 : 30 stones, Moon Phase indicator.
- 5R86 : 50 stones, day, GMT, Chronograph.
- 7R06 : 88 stones, Sonnerie.
- 7R68 : 30 stones, day.
- 7R88 : 30 stones, day.
- 7R99 : 32 stones.
- 9R65 : 30 stones, day.
- 9R66 : 30 stones, day, GMT.
- 9R86 : 50 stones, day, GMT, Chronograph.
Standard features:
- Time accuracy: Monthly rate within ±15 sec (equivalent to a daily rate of ±0.5 sec)
- Power reserve (72h) indicator.