Spring Drive

The Spring Drive is a watch movement that was developed by Seiko Epson through collaboration with Seiko Instruments and Seiko Holdings. Up-to-date, it is the only commercially available wristwatch embedded technology capable of truly creating a continuous movement of the second hand, instead of the traditional beats per time unit as seen in quartz or mechanical watches.

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 specified 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, Ananta 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 is the Credor Minute Repeater in rose gold priced at 33 million yen (over $400,000 USD) and can be considered a grand complication.