watch-knowledge


He-Arc applies cycloidal reducer to automatic winding system [Video]

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April 2012


Professor Christian Robert, a lecturer in microtechnical conception at Switzerland’s He-Arc (Haute Ecole Arc Ingénierie), and his students presented an application of the cycloidal reducer for displaying the hours and minutes on a watch dial last year.

This year, Professor Robert proposed two new applications of the cycloidal reducer (also known as the cycloidal drive or cycloidal speed reducer) in watch movements to his students: one for the automatic winding system and one for displaying the seconds.

He-Arc applies cycloidal reducer to automatic winding system
The cycloid reducer applied to an automatic winding system (20:1 scale model)

The main advantage of the cycloidal reducer in the automatic winding system is that since it replaces a number of the wheels and pinions in the gear train and has a high reduction factor, it allows a reduction in the space occupied by the movement and a 20 per cent improvement in the yield between the oscillating mass and the ratchet wheel.

When applied to the automatic winding mechanism, the cycloidal reducer modifies the gear train so that fewer rotations of the oscillating mass are required to wind the barrel, requiring 140 revolutions for one revolution of the ratchet wheel. The oscillating mass only turns freely in one direction and drives the cycloidal reducer in the other direction (since the cycloidal reducer can only work in one direction).

Since the movement can also be wound by hand using the crown (an ETA 2892 calibre was used as a basis for the mechanism), which would make the cycloidal reducer rotate too fast and cause premature wear, a mobile without a shaft that is held on an olive-shaped peg is used as a decoupling system to disconnect the cycloidal reducer for manual winding.

The application to display the seconds builds on the design presented last year in which the cycloidal reducer was used for the reduction between the minute and hour displays. A cycloidal reducer can also be used to display the seconds.