Spring Drive is an electro-mechanical watch movement technology from Seiko noted for extreme accuracy and timing precision.
Seiko began working on hybrid electronic/mechanical watches in the 1960's. They produced a number of electric watches which used a battery and motor for power and a conventional mechanical gear train and escapement for timing. They also produced the first successful mass-market quartz movements, initiating the quartz crisis and nearly destroying the Swiss and American watch business. Quartz watches use a battery and motor for motive force and a quartz oscillator rather than escapement for timing, making them extremely accurate and reliable.
In 1977, engineers at Suwa Seikosha invented a method of timekeeping for a mechanical watch using a rotating disc between electro-magnets. This concept differed dramatically from all earlier watch technologies (mechanical, electric, and quartz) in that the gear train is continually in motion, with no stop/start impulses, as is the case for a mechanical escapement, or intermittent movement, as in quartz.
The key to Spring Drive technology is the "tri-synchro regulator", which manages the mechanical energy of the mainspring, the electrical energy generated by the regulator, and the electromagnetic energy used to control the glide wheel. The speed of the glide wheel is measured 8 times per second and compared to a quartz timer, creating a feedback loop to brake the glide wheel or allow it to accelerate. The gear train is constantly in motion at very close to ideal speed, deviating by less than 1 second per day and allowing precise timing.
This concept was continually developed over the following two decades before being announced in 1997 and presented at the Basel Fair in 1998. A Spring Drive Credor was presented in 1999. The first Spring Drive movements were hand winding, with an automatic movement arriving in 2005.
Spring Drive technology is reserved for Seiko's high-end lines: Grand Seiko, Credor, Galante, Izul, Ananta, and Prospex. The Grand Seiko Chronograph is considered one of the most advanced and accurate chronographs in the world, while the Spring Drive Credor Minute Repeater is a $400,000 grande complication.
Seiko currently produces two Spring Drive movement families: