Riefler escapement

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In 1891 the Riefler escapement was invented for Observatory clocks. In the Riefler Clock, the energy required to keep the pendulum swinging is supplied by bending the suspension spring. The pendulum is not suspended from a fixed support, but instead the upper chops of the suspension spring rest on a bearer, which has two co-linear knife-edges on its underside. The bending point of the suspension spring is in alignment with the line of contact of the knife-edges and the planes or supports on which they rest. The spring will therefore be bent more than could be caused by the swing of the pendulum alone, and thus will provide the impulse for the next swing. The suspension spring is used to discharge the twin functions of suspension and giving impulse. It has a very good performance because the impulse and arc are nearly constant.

In the Riefler escapement, the pendulum is free of entanglement with the escape wheel for roughly two-thirds of each swing, and the only work it has to do is to unlock the escape wheel once per second. Even this operation is performed near the ideal place, which is when the pendulum is near the mid-swing.

The Riefler escape wheel and pallets are of a special design. There are actually two escape wheels mounted on the same shaft and two surfaces on each of the two pallet pins. The front wheel has teeth rather like a dead-beat escapement, and operate on the flat surface of the pallet to lock the wheel. The rear escape wheel has teeth cut in ratchet form with the sloping surface facing the direction of rotation. The round part of each pallet is acted upon by this surface to give impulse.

The impulse is delivered to the pendulum via the suspension spring, which helped "free" the pendulum from disturbance by the escapement. Two escape wheels are used—one for locking and one for impulse.

[edit] References

• http://users.actcom.co.il/meccano/riefler_clock.htm
• http://www.clockswatches.com/papers/dates.htm