Isochronism constitutes the essential element of any chronometry, which itself is based on oscillations of whatever kind, such as the oscillations of a pendulum, a quartz crystal or a balance. The more regular the oscillation, the more regular the chronometric performance of the movement and the better it can be adjusted for best possible accuracy. If a control mechanism oscillates perfectly evenly, it is called isochronous (Greek for “occurring at equal intervals”). In this context, the isochronism of the classical balance of portable mechanical watches has emerged as the greatest challenge for watchmakers and engineers. Major interference factors are primarily:
- the asymmetric development (transient and dying out oscillations, e.g. breath) of the spring,
- the changing elasticity of the spring depending on temperature,
- the influence of magnetic noise fields,
- mechanical and thermal material changes at both fixation points of the spring,
- the influence of the centrifugal and gravitational forces on the spring,
- the imbalance of the balance wheel,
- the play between the regulator pins.
The properties of the EPS® material alone do not suffice to solve the phenomenon of asymmetric development of a flat spiral spring. Our research team was therefore looking for a solution and found it in a new type of end curve design that could be realized within the oscillatory level of the spring. This is shown in a conspicuous thickening at the outer end, which forces the EPS® spring into a concentric development, making the transient and dying-out oscillation take place symmetrically to the centre of the spring on all sides of the oscillatory level. This ideal form of thickening was registered as a patent.
The EPS® spring is manufactured in one piece, which means it has an integrated collet for fixation to the balance shaft and at the outer end it is “clipped” into a very precisely defined area in the stud. The minute clamping jaws of this stud are designed to be resilient so that the clip-on point of the spring may still be corrected by pulling or pushing the spring through the stud. This new type of stud was registered as a patent.
On conventional springs, the inner end is affixed to the collet by soldering, welding or clamping. This causes a structural modification of the spring material at the fixation points due to squeezing or heating, which in turn requires additional adjustment work.
With our EPS® spring we have created an oscillating mechanism that provides several key advantages: The EPS® spring oscillation is ideally concentric. It is designed for isochronism independently of temperature, position of the movement and magnetic fields.
As in the case of the silicon escape wheel, the EPS® spring is produced in a DRIE etching process (Deep Reactive Ion Etching), which is described in more detail at a later stage. The material has a uniformly flawless polycrystalline structure and can be machined in the micrometer range. As a result, all EPS® springs are of consistently uniform and extremely high quality, which is in turn transferred onto the chronometric accuracy of the movement fitted with these.
The EPS ® spring reflects the consistent innovative policy of our manufactory. With this development, Damasko moved to the forefront of innovation and simultaneously sets decisive accents in order to endow their new products with a brand-specific exclusivity through significant distinguishing features. As in the case of the EPS spring, the aim of this innovative philosophy is to further increase the chronometric accuracy and stability of mechanical watches as well as the longevity and sustainable value of Damasko watches.