Virtual MEchanics GAthering -MEGA- Seminar: Flexure pivot oscillators for mechanical watches
2021-03-11 16:15 - 17:30 | https://epfl.zoom.us/s/84678428267 Passcode: [REDACTED] https://epfl.zoom.us/s/84678428267
Etienne Thalmann (INSTANT-LAB, EPFL)
Abstract It appears that the concerted efforts of the watchmaking industry are leading towards a limit in mechanical watch accuracy. The general consensus in horology is that the time base's quality factor needs to be improved in order to significantly increase timekeeper accuracy. The solution appears to be flexure oscillators in silicon. Indeed, flexure oscillators eliminate contact friction by using the elastic deformation of slender beams to guide the motion of an inertial body and monocrystalline silicon minimizes internal friction. The results is a significant improvement in quality factor in comparison to the traditional balance and hairspring oscillator. It is however not sufficient to increase the quality factor to reach accurate timekeeping. The period of oscillation of the time base must stay as regular as possible regardless of changes in operating conditions such as amplitude of oscillation, orientation with respect to gravity, temperature and shocks. This research focuses on minimizing the effects of amplitude (i.e., isochronism defect) 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 or inertia. The second technical contribution is a design method to reduce the effect of gravity for all orientations of the time base by ingeniously placing the flexures and exploiting the position of the center of mass. These findings were embodied in two novel flexure pivot architecture. A silicon prototype satisfying typical mechanical watch specifications was manufactured and used to validate our concepts experimentally.

Bio Etienne Thalmann received the MSc degree in Mechanical Engineering from EPFL in 2015. He conducted his Master’s thesis in control systems at the Swiss Center for Electronics and Microtechnology (CSEM), for which he was awarded the Hilti Mechatronic Prize. He then joined the Patek Philippe Chair in Micromechanical and Horological Design (Instant-Lab) at EPFL, where he completed his PhD on flexure pivot oscillators for mechanical watches in 2020. He is currently continuing his research on flexure oscillators with Prof. Simon Henein as postdoctoral researcher at Instant-Lab.
