Torsion Pendulum Clock - Mechanism

Mechanism

Torsion clocks are capable of running much longer between windings than clocks with an ordinary pendulum, because the torsion pendulum rotates slowly and takes little energy. However they are difficult to set up and are usually not as accurate as clocks with ordinary pendulums. One reason is that the oscillation period of the torsion pendulum changes with temperature due to temperature-dependent change in elasticity of the spring. The rate of the clock can be made faster or slower by an adjustment screw mechanism on the torsion pendulum that moves the weight balls in or out from the axis. The closer in the balls are, the smaller the moment of inertia of the torsion pendulum and the faster it will turn, like a spinning ice skater who pulls in her arms. This causes the clock to speed up.

One oscillation of the torsion pendulum usually takes 12, 15, or 20 seconds. The escapement mechanism, that changes the rotational motion of the clock's gears to pulses to drive the torsion pendulum, works rather like an anchor escapement. A crutch device at the top of the torsion spring engages a lever with two anchor-shaped arms; the arms in turn alternately engage the teeth of the escape wheel. As the anchor releases a tooth of the escape wheel, the lever, which is fixed to the anchor, moves to one side and, via the crutch, gives a small twist to the top of the torsion spring. This is just enough to keep the oscillation going.

The Atmos clock, made by Jaeger Le Coultre, is a type of torsion clock which doesn't need to be wound or powered at all. The mainspring which turns the clock's wheels is kept wound by small changes in atmospheric pressure and/or local temperature, using a bellows mechanism. Thus no winding key or battery is needed, and it can run for years without human intervention.