Seiko

I've been struggling through some patent documents this morning in an effort to understand the Spring Drive's torque return system.

( feel free to join me; they are HERE )

I had noticed some extra wheels on the movements and wondered what they do.

Now I know they relate to the functions of the torque return system on Spring Drive movements. 

I will attempt to summarize:

At certain times any mainspring produces more torque than the movement needs (this is because power off the spring is not linear from fully to unwound)

At other times the torque is too low and movement accuracy suffers.

The fusee chain drive system is one answer to this problem, but it is expensive, bulky and overly complex. 

The Spring Drive movement has a few extra small gear wheels and a clutch assembly located near the mainspring barrel. 

These serve to prevent excess torque from driving the movement "too hard" or "too fast".

Excess torque is instead returned to the mainspring and somehow "rewinds" it on the sly, assisting the rotor or doing it independently on a manual wind watch.

This set of wheels also supplies a signal to the power reserve hand to indicate the number of winds on the barrel.

Have you noticed that virtually all Spring Drive watches have power reserve indicators?

By using this system, Seiko Epson can

- extend the autonomy (running time) about 25% 
- lower the maximum forces going through the movement (longer life; reduced maintenance)
- reduce the size of the glide wheel, generator, etc to optimum levels
- use a conventionally sized spring and barrel while still achieving excellent performance
- switch off "rewinding" circuit when power drops to a predetermined level, allowing all remaining mainspring power to the movement
- switch off the movement when mainspring unwinds to a predetermined point 
- finally, because these wheels are small, they can be placed in a convenient location that is otherwise unused

Remember the Seiko Epson mantra?  It's COMPACT, ENERGY-SAVINGS and HIGH PRECISION. 

That seems to summarize the intent of the torque return system. I am impressed even more than before.

Cazalea

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