MEchanics GAthering -MEGA- Seminar: Flexure Pivot Oscillators for Mechanical Watches

It appears that the concerted efforts of the watchmaking industry are leading towards a limit in the accuracy of mechanical watches. The general consensus in horology is that the quality factor of the time base, a dimensionless number that characterizes the damping of an oscillator, needs to be improved for the accuracy of the timekeeper to increase. The three classical mechanical time bases all suffer from limitations in the context of a mechanical watch application. The solution appears to be flexure pivot oscillators in silicon. The use of flexures instead of bearings eliminates contact friction and the choice of monocrystalline silicon minimizes internal friction, leading to significant improvements in quality factor in comparison to balance spring oscillators. 
Accurate timekeeping requires the period of oscillation of the time base to stays as regular as possible regardless of changes in operating conditions such as amplitude of oscillation and orientation with respect to gravity. We focus on minimizing the effects of amplitude and gravity that arise from the use of flexures. The first technical contribution is to note that the isochronism defect is a second order phenomenon, and to deal with it by modifying the second order behavior of flexure spring stiffness and inertia. The second technical contribution is a design method to make the effect of gravity constant for all orientations of the time base by ingeniously placing the flexures and exploiting the position of the center of mass. These findings are embodied in two new flexure pivot architectures called Gravity Insensitive Flexure Pivot (GIFP), co-RCC flexure pivot oscillator (co-RCC) and Rotation-Dilation Coupled Oscillator (RDCO). A silicon prototype satisfying typical mechanical watch specifications is manufactured. The technical contributions of the thesis are validated by finite element simulations and experimental measurements on the prototype.