Torsion pendulum clock - AbsoluteAstronomy.com

A torsion pendulum clock, or torsion clock, is a mechanical clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

which keeps time with a mechanism called a torsion pendulum

Torsion spring

A torsion spring is a spring that works by torsion or twisting; that is, a flexible elastic object that stores mechanical energy when it is twisted. The amount of force it exerts is proportional to the amount it is twisted. There are two types...

. This is a weighted disk or wheel, often a decorative wheel with 3 or 4 chrome balls on ornate spokes, suspended by a thin wire or ribbon called a torsion spring

Torsion spring

. The torsion pendulum rotates about the vertical axis of the wire, twisting it, instead of swinging like an ordinary pendulum

Pendulum

A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

. The force of the twisting torsion spring reverses the direction of rotation, so the torsion pendulum oscillates slowly, clockwise and counterclockwise. The clock's gears apply a pulse of torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

to the top of the torsion spring each rotation to keep the wheel going. The wheel and torsion spring function similarly to a watch

Watch

A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

's balance wheel

Balance wheel

The balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring...

and hairspring

Balance spring

A balance spring, or hairspring, is a part used in mechanical timepieces. The balance spring, attached to the balance wheel, controls the speed at which the wheels of the timepiece turn, and thus the rate of movement of the hands...

, as a harmonic oscillator

Harmonic oscillator

In classical mechanics, a harmonic oscillator is a system that, when displaced from its equilibrium position, experiences a restoring force, F, proportional to the displacement, x: \vec F = -k \vec x \, where k is a positive constant....

to control the rate of the clock's hands.

Description

Torsion clocks are usually delicate, ornamental, spring-wound

Mainspring

A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

mantel clock

Mantel clock

Mantel clocks — or shelf clocks — are relatively small house clocks traditionally placed on the shelf, or mantel, above the fireplace. The form, first developed in France in the 1750s, can be distinguished from earlier chamber clocks of similar size due to a lack of carrying handles.These clocks...

s. The polished clock mechanism is exposed under a glass case or dome, to allow people to watch the torsion pendulum turn. Clocks of this style, first made by Anton Harder around 1880, are also known as 400-day or anniversary clocks, because many of them only have to be wound once a year.

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

Moment of inertia

In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...

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

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

mechanism, that changes the rotational motion of the clock's gears to pulses to drive the torsion pendulum, works rather like an anchor escapement

Anchor escapement

In horology, the recoil or anchor escapement is a type of escapement used in pendulum clocks. An escapement is the mechanism in a mechanical clock that maintains the swing of the pendulum and allows the clock's wheels to advance a fixed amount with each swing, moving the hands forward...

. 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

Atmos clock

Atmos is the brand name of a mechanical clock manufactured by Jaeger-LeCoultre in Switzerland which does not need to be wound manually. It gets the energy it needs to run from temperature and atmospheric pressure changes in the environment, and can run for years without human intervention.Its...

, made by Jaeger Le Coultre, is a type of torsion clock which doesn't need to be wound or powered at all. The mainspring

Mainspring

which turns the clock's wheels is kept wound by small changes in atmospheric pressure and/or local temperature, using a bellows

Bellows

A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...

mechanism. Thus no winding key or battery is needed, and it can run for years without human intervention.

History

The torsion pendulum was invented by Robert Leslie in 1793. The torsion pendulum clock was first invented and patented by American Aaron Crane in 1841. He made clocks that would run up to one year on a winding. He also attempted to make precision astronomical regulator clocks based on the torsion pendulum, but only four sold.

The German Anton Harder apparently independently invented and patented the torsion clock in 1879-1880. He was inspired by watching a hanging chandelier rotate after a servant had turned it to light the candles. He formed the firm Jahresuhrenfabrik ('Year Clock Factory') and designed a clock that would run for a year, but its accuracy was bad. He sold the patent in 1884 to F. A. L. deGruyter of Amsterdam, who allowed the patent to expire in 1887. Other firms entered the market, beginning the German mass production of these clocks.

Although they were successful commercially, torsion clocks remained poor timekeepers. In 1951, Charles Terwilliger of the Horolovar Co. invented a temperature compensating suspension spring, which allowed fairly accurate clocks to be made.

External links

International 400-day Clock Chapter #168, NAWCC, retrieved Aug. 30, 2007. Torsion clock branch of large clock collectors club. Publishes quarterly journal Torsion Times.
Torsion clock gallery, Horology Web Ring, webhorology.com, retrieved Aug. 30, 2007. Pictures of torsion clocks from several private collections.
Torsion clock collection, Battersea Clock Home, Flickr.com, retrieved Aug. 29, 2007. Pictures of a collection of 30 anniversary clocks in London, UK.
The Danish Telavox (later Clementa) battery driven torsion pendulum clock. A collector's guide illustrating the history and varieties of cases and movements from 1942-1977 (?).

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