Dynamics of high frequency oscillators for mechanical watches

The main mechanical issues that lead to poor chronometric performances of the mechanical regulator can be divided into three broad classes: chronometric errors due to the position or the watch in space; chronometric errors due to the variation of the driving torque; and chronometric errors due to the disturbances of the free oscillation phase of the oscillating system generated by the escapement.

An innovative mechanical regulator for wrist watches has been developed, characterized by an escapement system that reduces the negative influence of the escapement device on the isochronism of the oscillator. The solution relies on a monolithic oscillator with a compliant hinge coupled to a deadbeat escapement. This design is completely different compared to the traditional swiss anchor escapement interacting with an oscillator characterized by a flywheel, hairspring and balance shaft.

A methodology to assess and optimize the design and the chronometric performances of the new mechanical regulator has been developed. The elasto-kinematic optimization of the oscillator is carried out using a FE model in order to guarantee the best dynamic performances and mechanical integrity of the device taking advantage of the orthotropic elastic behavior of monocrystalline silicon. Particular attention is devoted to the oscillating system. An accurate evaluation and classification of the damping phenomena acting at the macro and micro scale is carried out through CFD simulations. The main contribution to the overall damping is associated to the aerodynamic drag forces acting on the oscillator.

The modelling of the entire mechanical regulator by means of multi-body techniques allows faster simulations as compared to FE ones. The escapement mechanism is modelled using inertial, damping and stiffness properties of the oscillator. The developed methodology based on coupled FE, CFD and multi-body models is new in the field of mechanical watchmaking, allowing an optimized design or the device that satisfies structural requirements, including identification of the quality factor. The resulting chronometric performances of the developed mechanism are significantly better than those of high end mechanical regulators used nowadays.

Source: Elsevier

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