Escapement
The sudden stopping of the escapement's tooth is what generates the characteristic "ticking" sound heard in operating mechanical clocks and watches.
[4][5][6] The earliest liquid-driven escapement was described by the Greek engineer Philo of Byzantium in the 3rd century BC in chapter 31 of his technical treatise Pneumatics, as part of a washstand.
[7] A counterweighted spoon, supplied by a water tank, tips over in a basin when full, releasing a spherical piece of pumice in the process.
The next two centuries, the "golden age" of mechanical horology, saw the invention of over 300 escapement designs, although only about ten of these were ever widely used in clocks and watches.
The tourbillon was invented to minimize this: the balance and spring are put in a cage that rotates (typically but not necessarily, once a minute), smoothing gravitational distortions.
This very clever and sophisticated clockwork is a prized complication in wristwatches, even though the natural movement of the wearer tends to smooth gravitational influences anyway.
Since 1658 when the introduction of the pendulum and balance spring made accurate timepieces possible, it has been estimated that more than three hundred different mechanical escapements have been devised, but only about 10 have seen widespread use.
In the 20th century, electric timekeeping methods replaced mechanical clocks and watches, so escapement design became a little-known curiosity.
The son began construction of a prototype, but both he and Galileo died before it was completed.Invented around 1657 by Robert Hooke, the anchor (see animation) quickly superseded the verge to become the standard escapement used in pendulum clocks through to the 19th century.
[43] The early form was invented by Pierre Le Roy in 1748, who created a pivoted detent type of escapement, though this was theoretically deficient.
[47] John Arnold was the first to use the detent escapement with an overcoil balance spring (patented 1782), and with this improvement his watches were the first truly accurate pocket timekeepers, keeping time to within 1 or 2 seconds per day.
Clockmakers found it suffered from excessive wear, so it was not much used during the 18th century, except in a few high-end watches with cylinders made from ruby.
[49] The duplex watch escapement was invented by Robert Hooke around 1700, improved by Jean Baptiste Dutertre and Pierre Le Roy, and put in final form by Thomas Tyrer, who patented it in 1782.
Then the next locking tooth drops onto the ruby roller and stays there while the balance wheel completes its cycle and swings back clockwise, and the process repeats.
[59] However, it lost favor to the lever escapement; its tight tolerances and sensitivity to shock made duplex watches unsuitable for active people.
Like the chronometer, it is not self-starting and is vulnerable to "setting"—if a sudden jar stops the balance during its clockwise swing, it cannot restart.
In a real escapement, these impacts give rise to loud audible "ticks" (indicated in the animation by the appearance of an asterisk (*) beside the locking blocks).
They cause the weighted gravity arms to be raised by an amount indicated by the pair of parallel lines on each side of the escapement.
For the Trinity College Cambridge Clock, a mass of around 50 grams is lifted through 3 mm each 1.5 seconds, which works out to 1 mW of power.
The great clock in Elizabeth Tower at Westminster that rings London's Big Ben uses a double three-legged gravity escapement.
Daniels' coaxial escapement, however, achieves a double impulse with passive lever pallets serving only to lock and unlock the larger wheel.
[citation needed] This mode of impulse is in theory superior to the lever escapement, which has engaging friction on the entry pallet.
The independent watchmaker, De Bethune, has developed a concept where a magnet makes a resonator vibrate at high frequency, replacing the traditional balance spring.
In 1843, Matthäus Hipp first mentioned a purely mechanical clock being driven by a switch called "echappement à palette".
As well as the counting pawl, the pendulum carried a small vane, known as a Hipp's toggle, pivoted at the top, which was completely free to swing.
If the arc was too small the vane never left the far side of the groove, and when the pendulum swung back it pushed the block strongly downwards.
[79] A gathering arm attached to the pendulum moves a 15-tooth count wheel in one position, with a pawl preventing movement in the reverse direction.
[80] In the 20th century, the English horologist William Hamilton Shortt invented a free pendulum clock, patented in September 1921 and manufactured by the Synchronome Company, with an accuracy of one-hundredth of a second a day.
In this system, the timekeeping "master" pendulum—whose rod is made from a special steel-nickel alloy ( Invar) and whose length changes very little with temperature—swings as free of external influence as possible sealed in a vacuum chamber; it does virtually no work.
The slave pendulum was adjusted to run slightly slow, such that on approximately every other synchronization pulse the spring would be caught by the armature.
