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LORENZ FÖRSTER, NÜRNBERG, GERMANY, c. 1880

Below is a drawing depicting what the Germans call a "freischwingendes"or "freischwinger" pendulum which translated means a free swinging or free swinger pendulum. This was invented by the tower clock maker Joseph Mannhardt, Münich, Germany. While this is really not strictly the case, it did make the pendulum much more detached from the movement than a conventional pendulum. In this design there is a count wheel attached to the pendulum. This is advanced with each period of pendulum swing one tooth. In this way the pendulum is slightly attached, but very much less so as it is not doing any of the work of  locking or unlocking of the escape wheel under the the power of the main going train which a conventional pendulum must do. Mounted to this wheel is a finger that when brought into position (in the case below twice per revolution of the count wheel, in the case of the Förster, once) trips a lever that unlocks the going train. This sets into motion a set of levers and cam that allow a roller to contact an incline ramp also attached to the pendulum. The energy imparted by the weight of the roller against the incline ramp gives the pendulum an impulse. This must be synchronized in such a way so that the roller comes into contact just as the pendulum begins to swing in the direction of the upward incline of the ramp (in this case as well as the Förster, to the left). The roller must also be brought back to its starting position before the pendulum begins to swing back again so as not to touch the ramp until called upon by the count wheel at the next cycle. In this case the pendulum definitely receives an impulse function in the conventional sense. The speed at which this all takes place is mediated by the fly located in a "key hole"area of the pendulum.

What this design achieves is the vast diminution of the locking and unlocking function though the count wheel; with the impulse being received at far more infrequent intervals than would be in a normal pendulum /escapement system. All of the rest of the time the pendulum swings with little disturbance. The quiescent period can vary depending of the length of the pendulum and the configuration of the count wheel - generally from 30 seconds to one minute, the Förster being 40 seconds. Theoretically this detaches the pendulum far more than conventionally, achieving greater accuracy. On the negative side, the impulse that is given, while infrequent, must  be of a greater amount because the pendulum looses more energy during the long quiescent period than it would during the short one second interval in a conventional deadbeat escapement. This results in a more violent release of energy to the pendulum than would otherwise be. Whether this negates the positive factors of this design is unknown. It seems that this design was used exclusively by German makers on their larger, more expensive movements.

It certainly is a far more expensive system to make than any conventional or gravity escapement and probably more than a conventional escapement equipped with a most type of remontoire. This system, I hesitate to call it an escapement as it is more of a timer, contains elements of a remontoire in that there is a cycling of the going train at determinate intervals mediated by an air brake (fly fan). It also has elements of a gravity escapement, whereby the impulse is delivered by a mass of the same amount at identical intervals directly to the pendulum, has no sliding friction and thus requires no oil.

            Forster (13).jpg (309614 bytes)

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