Setting the auto wind system aside and removing the train wheel bridge, we can trace the flow of mechanical power through the Spring Drive.  

As shown above, the barrel, with main spring, is set at point "A". Notice the jeweled hole for the barrel arbor to reduce friction. Mechanical energy from the barrel is transferred from the barrel to wheels "B", "C", "D", and "E" to glide wheel "F".  

It's the glide wheel "F" that is responsible for regulating the time keeping of the watch.

The glide wheel (above) is not to be confused with the balance wheel of a conventional mechanical watch, it is totally different. Instead of oscillating back and forth under the influence of a hair spring, it rotates constantly, and silently, in one direction at EXACTLY eight revolutions per second. The glide wheel provides constant stability and permanency of rate which are major improvements when compared with a conventional balance wheel.
 

In order to be controlled to such an exacting speed of rotation, a pure iron stator (a strong permanent magnet) "A" (above) is fit to the glide wheel.  

The stator serves several roles in the operation of the Spring Drive movement. First, upon initial start of the watch, the glide wheel (and stator) is allowed to spin freely for one second generating enough electrical power to energize the control circuit. After initial starting and the control circuit taking control of the watch, the stator acts as a brake to regulate the glide wheel's speed at eight revolutions per second. If it wasn't for the stator, the glide wheel would spin freely at several thousand revolutions per minute (and time would really fly!) The stator also sends one pulse per revolution to the control circuit that indicates the exact speed of the glide wheel, allowing eight corrections per second if required.

Removing a few more components we can see the control circuitry (above).  

The glide wheel, with stator, is positioned at point "A". Two coils "B" surround the stator, without touching it, Seiko improved the performance of these coils by developing a method for winding them especially tight and even. These coils, combined with the stator, serve two purposes: acting as an electronic brake to control the glide wheel speed, and generating the minute amount of electricity needed to power the control circuit "C." It's the control circuit that is the brain of the system, via feedback from the stator, dictating when the glide wheel should be slowed slightly or allowed to spin slightly faster.
 

I suppose we could say that the stator, coils, and control circuit are the cruise-control that keeps the glide wheel rotating at exactly eight revolutions per second, and marking the time within 1 second per day!

A small window offers a nice view of the glide wheel. Notice the sharp beveling of the plates and bridges. Although the beveling is done via machine, it adds a crisp flavor to the watch.

For comparison, the upper row of parts above are the major components of the Spring Drive, while the bottom row is that of a conventional mechanical watch.

The Spring Drive has a power reserve of 72 hours, about 24 hours more than most single barrel watches. A series of gears transmits the power information from the barrel to the dial. 

Continue to Part 3 of the Article

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