Development of Silicon Escape Wheel to Improve Escapement Efficiency

Abstract

  Mechanical watches need to run for longer. A thinner, longer mainspring was used to increase the running time without increasing the size of the movement. The thinner mainspring reduces the torque of the barrel, which reduces the amplitude of the balance wheel and may cause poor watch accuracy. The escape wheel was made from silicon instead of alloy in order to reduce the energy consumed by the escapement. Silicon is expected to reduce the amount of engagement and the moment of inertia. The silicon wheels were fabricated using a simple process with only a single photolithography and etching step. The surface was smoothed using thermal oxidation and removal to prevent chipping. Since silicon is a brittle material and cannot be press-fitted, a unique mating design was devised. In addition, a metal washer was used to prevent the wheel from slipping off the pinion. In the movement using the silicon wheel, the energy transmitted from the barrel to the balance wheel was improved by about 30%. As a result, it was possible to increase running time by more than 20 hours at the same or higher amplitude. In addition, the movement equipped with a silicon wheel has passed our internal standards for reliability tests. A three-layer film structure has been formed to achieve a vivid blue color with a reflectance of more than 50% at 450-550 nm. The silicon escape wheel enabled us to improve both the practicality and the aesthetic appeal of the watch.