Pendulum clock

Pendulum clock conceived by Galileo Galilei around 1637. The earliest known pendulum clock design, it was never completed.

Vienna regulator style pendulum wall clock

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Escapement

Main article: Escapement

Animation of an anchor escapement, one of the most common escapements used in pendulum clocks

The escapement is a mechanical linkage that converts the force from the clock's wheel train into impulses that keep the pendulum swinging back and forth. It is the part that makes the "ticking" sound in a working pendulum clock. Most escapements consist of a wheel with pointed teeth called the escape wheel which is turned by the clock's wheel train, and surfaces the teeth push against, called pallets. During most of the pendulum's swing the wheel is prevented from turning because a tooth is resting against one of the pallets; this is called the "locked" state. Each swing of the pendulum a pallet releases a tooth of the escape wheel. The wheel rotates forward a fixed amount until a tooth catches on the other pallet. These releases allow the clock's wheel train to advance a fixed amount with each swing, moving the hands forward at a constant rate, controlled by the pendulum.

Although the escapement is necessary, its force disturbs the natural motion of the pendulum, and in precision pendulum clocks this was often the limiting factor on the accuracy of the clock. Different escapements have been used in pendulum clocks over the years to try to solve this problem. In the 18th and 19th centuries, escapement design was at the forefront of timekeeping advances. The anchor escapement (see animation) was the standard escapement used until the 1800s when an improved version, the deadbeat escapement, took over in precision clocks. It is used in almost all pendulum clocks today. The remontoire, a small spring mechanism rewound at intervals which serves to isolate the escapement from the varying force of the wheel train, was used in a few precision clocks. In tower clocks the wheel train must turn the large hands on the clock face on the outside of the building, and the weight of these hands, varying with snow and ice buildup, put a varying load on the wheel train. Gravity escapements were used in tower clocks.

By the end of the 19th century specialized escapements were used in the most accurate clocks, called astronomical regulators, which were employed in naval observatories and for scientific research. The Riefler escapement, used in Clemens-Riefler regulator clocks was accurate to 10 milliseconds per day. Electromagnetic escapements, which used a switch or phototube to turn on a solenoid electromagnet to give the pendulum an impulse without requiring a mechanical linkage, were developed. The most accurate pendulum clock was the Shortt-Synchronome clock, a complicated electromechanical clock with two pendulums developed in 1923 by W.H. Shortt and Frank Hope-Jones, which was accurate to better than one second per year. A slave pendulum in a separate clock was linked by an electric circuit and electromagnets to a master pendulum in a vacuum tank. The slave pendulum performed the timekeeping functions, leaving the master pendulum to swing virtually undisturbed by outside influences. In the 1920s the Shortt-Synchronome briefly became the highest standard for timekeeping in observatories before quartz clocks superseded pendulum clocks as precision time standards.

Time indication

The indicating system is almost always the traditional dial with moving hour and minute hands. Many clocks have a small third hand indicating seconds on a subsidiary dial. Pendulum clocks are usually designed to be set by opening the glass face cover and manually pushing the minute hand around the dial to the correct time. The minute hand is mounted on a slipping friction sleeve which allows it to be turned on its arbor. The hour hand is driven not from the wheel train but from the minute hand's shaft through a small set of gears, so rotating the minute hand manually also sets the hour hand.

Maintenance and Repair

Pendulum clocks are long lived and don't require a lot of maintenance, which is one reason for their popularity.

As in any mechanism with moving parts, regular cleaning and lubrication is required. Specific low viscosity lubricants have been developed for clocks, one of the most widely used being a polyalcanoate synthetic oil.

Springs and pins may wear out and break and need replacing.

Styles

One-Year German Regulator Clock. Circa 1850

Pendulum clocks were more than simply utilitarian timekeepers; due to their high cost they were status symbols that expressed the wealth and culture of their owners. They evolved in a number of traditional styles, specific to different countries and times as well as their intended use. Case styles somewhat reflect the furniture styles popular during the period. Experts can often pinpoint when an antique clock was made within a few decades by subtle differences in their cases and faces. These are some of the different styles of pendulum clocks:

• Act of Parliament clock
• Anniversary clock (uses a torsion pendulum)
• Banjo clock
• Bracket clock
• Cartel clock
• Comtoise or Morbier clock
• Crystal regulator
• Cuckoo clock
• Grandfather clock
• Lantern clock
• Mantel clock
• Master clock
• Ogee clock
• Pillar clock
• Schoolhouse regulator
• Torsion pendulum clock
• Turret clock
• Vienna regulator
• Zaandam clock

See also

• Pendulum (mathematics)
• Cycloidal pendulum
• Flying pendulum clock
• Steam clock
• Balance spring (hairspring)

External links

• The Invention of Clocks
• The (Not So) Simple Pendulum
• The earliest Dutch and French Pendulum clocks, 1657-1662
• Computer-Aided Design and Kinematic Simulation of Huygens's Pendulum Clock