Riefler clock

The Riefler escapement is a mechanical escapement for precision pendulum clocks invented and patented by German instrument maker Sigmund Riefler in 1889. It was used in the astronomical regulator clocks made by his German firm Clemens Riefler from 1890 to 1965, which were perhaps the most accurate all-mechanical pendulum clocks made.

An escapement is the mechanism in a mechanical clock that gives the pendulum precise impulses to keep it swinging, and allows the gear train to advance a set amount with each pendulum swing. The Riefler escapement was an improvement of the deadbeat escapement, the standard used in precision clocks. In the deadbeat, the force to keep the pendulum swinging is applied by the teeth of the escape wheel sliding alternately against two angled pallets on arms attached to the pendulum. Therefore, slight variations in the friction of the pallets and in the torque from the escape wheel are passed on to the pendulum, disturbing its motion.

In the Riefler escapement, the energy required to keep the pendulum swinging is instead supplied by bending the short straight spring strip which suspends the pendulum. The upper end of the suspension spring is not attached to a fixed support as in most clocks, but instead is attached to a heavy metal bearer, which pivots on two aligned knife-edges on its underside which rest on flat agate plates. The bending point of the suspension spring is in alignment with the line of contact of the knife-edges. When the pendulum passes its bottom point, the escape wheel is unlocked and pushes the bearer, and the bearer pivots suddenly on its knife edges by a small angle, flexing the spring. The spring is bent by a small amount in addition to that caused by the swing of the pendulum, and thus provides the impulse for the next swing. So the suspension spring is used for two functions: suspending the pendulum and giving it impulse.

The escapement has better performance than the deadbeat because the force from the pallets, with its variability, is applied not to the pendulum but to the bearer. The escapement has no contact with the pendulum below the suspension spring. The pendulum is free of disturbance from the escape wheel for most of each swing and the only work it has to do is to unlock the escape wheel once per second. This operation is performed near the ideal place, at the center of each swing.

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