Balance spring for forming sprung balance resonator of mechanical watch, has hair springs whose curves correspond to specific relation so as to reduce displacements of center of mass of balance spring during contraction and expansion

摘要

The spring (1) has a hair spring (3) and another hair spring (5) whose curves respectively extend in two planes, where the spring is made of silicon. An attachment member (4) secures ends of the curves so as to form a dual balance spring in series. Each of the curves has a continuously variable pitch, and is symmetrical, relative to a line parallel to the planes passing via a median projection plane of the member. Each curve corresponds to a specific relation so as to reduce displacements of center of mass of the spring during contraction and expansion.