DonCorson
[AHCI]
3358
The Genequand Regulator – SSC Study Day 2014
The Genequand Regulator – SSC Study Day 2014
Coming back to the Société Suisse de Chronométrie (SSC) Study Day in September (for my article about the IsoSpring regulator also presented at this event click here), let's take a look at the Genequand regulator. The following is my résumé and translation of the presentation at the SSC Study Day.
The Geneguand regulator was conceived by Mr. Pierre Genequand, see the picture below, as a way to increase the autonomy of a mechanical watch to over a month. Mr. Genequand is a retired researcher from the CSEM (Swiss Center for Electronics and Microtechnology) in Neuchâtel and was used to using positioning elements with flexible members in optical and astronomic experiments. These positioning elements have no pivots making them more precise, eliminating hysteresis and wear. His goal was to make horological components with high precision and very low losses using flexible members instead of pivots.
Mr. Genequand and the first working model
After making an initial prototype scale 20:1 Mr. Genequand could convince the CSEM to develop the idea further at a scale 5:1. At this point the Vaucher Manufacture Fleurier joined the endeavour to integrate the Genequand regulator into a real watch movement.
The Genequand regulator comprises 3 main parts: 1) the oscillator (balance and hair spring), the escapement (anchor and escape wheel), and the isochronism corrector. These parts are all made of silicon using “Deep Reactive Ion Etching” or DRIE.
The balance wheel with Wittrick pivot
Silicon has ideal properties for the realisation of an oscillator for a watch. These include:
- nearly ideal elastic properties without hysteresis.
- high rupture strength
- Si can be machined with a very high precision using DRIE.
- Low coefficient of friction Si on Si.
- amagnetic
- corrosion resistant
- low density
To increase the autonomy of a watch it is necessary to reduce the losses in the regulator. These losses include the friction in the balance and anchor pivots and at the pallets. Pivots using flexible members have no frictional losses other than those in the flexible material itself. Such pivots are known as Wittrick pivots after H. W. Wittrick who did the first theoretical studies of them in the 1940's. The disadvantage of such pivots is the limited angle of rotation which maxes out at about 20° and a small displacement of the pivot point during the rotation. The implementations used here use rotation angles of about 15°. As the flexible members have a restoring force the pivot intrinsically includes the hair spring, so the balance, pivot and hair spring become one single part.
Of course, reducing the rotation angle has the advantage that the energy needed to sustain the oscillation is also reduced, thus increasing the autonomy. The disadvantage of the limited rotation angle is that the system becomes more sensitive to external disturbances. This can be counterbalanced by increasing the frequency, in this case to 12 Hz from the 4 Hz used in a classical watch oscillator. This increase in frequency reduces the autonomy, but without putting the 30 day goal in danger.
The advantages claimed of this oscillator are:
- high quality factor (around 1000 compared to a classical watch oscillator of around 250)
- long autonomy
- elimination of oil ageing problems as oil not used
- long term reliability, reduced maintenance.
The escapement of the Genequand regulator is also made using a Wittrick pivot to eliminate the pivot friction. The escapement used is based on the ideas of the Harrison grasshopper escapement with the utilisation of flexible pallets instead of the counter weighted pallets used by Harrison. Harrison's weighted pallets mean, of course, that the escapement will only work in one orientation to gravity, not possible for use in a watch. The use of flexible pallets allows the escapement to work in any position.
The escapement works as follows: At each swing of the balance one of the flexible pallets meshes with the escape wheel initially pushing it back a small amount. This small movement permits the other pallet to escape. Then the escape wheel pushes back on the meshed pallet, the energy being transmitted to the balance wheel until on the next swing the other pallet pushes back the escape wheel releasing the first pallet, etc..
The anchor and escape wheel
This second element of the Genequand regulator is, like the oscillator, fabricated in silicon. The precision of silicon machining, the good coefficient of friction and the low density (i.e. low weight) being decisive properties for this application.
The third element of the Genequand regulator is the isochonism corrector. This element is made necessary by the small variation in the restoring force of the Wittrick pivot and the characteristics of the escapement used.
The rigidity of the Wittrick pivot increases slightly with the amplitude of oscillation. As such the period of the oscillation will depend on the amplitude. At the same time as one of the pallets is always in contact with the escape wheel transmitting it's force to the anchor this type of escapement is more exposed to variations in the maintaining force. The isochronism corrector was designed to correct these two errors by acting on the anchor to make the frequency of the oscillator independent of the amplitude of the oscillations.
The Isochronism corrector
The silicon parts necessary for the movement were made at the MEMS foundry of the CSEM in Neuchâtel. The most complicated parts are the balance and the anchor with the two flexible blades composing their pivots on two different levels. These were made using a SOI (silicon on insulator) substrate and etching from both sides. The pieces were made with tolerances of less than +- 1 micron.
The complete Genequand Regulator system
The Genequand regulator has been integrated into the Vaucher caliber VMF 6000 that has been adapted as necessary to have the frequency and torque required. Six movements have been made. 5 are being used to characterize the system, the sixth is a demonstrator that is running continuously. The characterisation has shown the high quality factor expected with a value of about 1000. The compensator is working as expected and the energy necessary to maintain the system is less than a classical escapement by a factor of about 10. The minimum energy necessary to maintain the oscillations ais about 10 nJ. This is the confirmation that a caliber with this escapement can have an autonomy of more than one month. 
For thos who have not seen it in my first posting of the Vaucher press release, here is the Vaucher video about the Genequand Regulator again.
Image sources: the images are from the CSEM press release, but were copied from different pages on the Internet as the CSEM web site has been down for several days now.
This message has been edited by DonCorson on 2014-12-30 06:49:31
The Genequand Regulator – SSC Study Day 2014
That is amazing...
Still much to do...
