Patent ID: 9004748
Filing Date: 2015-04-14
Classification: G04B

Abstract:
1. A balance spring comprising: a first hairspring, a curve of which extends in a first plane and an inner coil of which includes a collet, a second hairspring, a curve of which extends in a second plane parallel to the first plane, and an attachment member securing an outer coil of the first hairspring to one end of the second hairspring so as to form a dual balance spring in series, wherein the curve of the first hairspring and the curve of the second hairspring each have a continuously variable pitch and are symmetrical relative to a straight line parallel to the first and second planes and pass through a median plane of projection of the attachment member and each curve being such that the following relation is zero: where: {right arrow over (P)} L is a length of the balance spring; s {right arrow over (x)}(s) is a parameterization of the balance spring by the curvilinear abscissa thereof; so as to reduce displacements of a centre of mass thereof during contraction and expansion, and each hairspring further includes at least two counterweights so as to compensate for an unbalance formed by a mass of the attachment member and personalize an anisochronism slope of the balance spring.