What is "lever escapement"

Lever \Le"ver\ (l[=e]"v[~e]r or l[e^]v"[~e]r; 277), n. [OE. levour, OF. leveor, prop., a lifter, fr. F. lever to raise, L. levare; akin to levis light in weight, E. levity, and perh. to E. light not heavy: cf. F. levier. Cf. Alleviate, Elevate, Leaven, Legerdemain, Levee, Levy, n.]

1. (Mech.) A rigid piece which is capable of turning about one point, or axis (the fulcrum), and in which are two or more other points where forces are applied; -- used for transmitting and modifying force and motion. Specif., a bar of metal, wood, or other rigid substance, used to exert a pressure, or sustain a weight, at one point of its length, by receiving a force or power at a second, and turning at a third on a fixed point called a fulcrum. It is usually named as the first of the six mechanical powers, and is of three kinds, according as either the fulcrum F, the weight W, or the power P, respectively, is situated between the other two, as in the figures.

2. (Mach.)

   1. A bar, as a capstan bar, applied to a rotatory piece to turn it.

   2. An arm on a rock shaft, to give motion to the shaft or to obtain motion from it.

      Compound lever, a machine consisting of two or more levers acting upon each other.

      Lever escapement. See Escapement.

      Lever jack. See Jack, n., 5.

      Lever watch, a watch having a vibrating lever to connect the action of the escape wheel with that of the balance.

      Universal lever, a machine formed by a combination of a lever with the wheel and axle, in such a manner as to convert the reciprocating motion of the lever into a continued rectilinear motion of some body to which the power is applied.

The lever escapement is a type of escapement that is used in almost all mechanical watches, as well as small mechanical non- pendulum clocks, alarm clocks, and kitchen timers. An escapement is a mechanical linkage that gives pushes to the timepiece's balance wheel, keeping it rotating back and forth, and with each swing of the balance wheel allows the timepiece's gear train to advance a fixed amount, thus moving the hands forward at a steady rate. The escapement is what makes the "ticking" sound in mechanical watches and clocks. The lever escapement was invented by British clockmaker Thomas Mudge around 1755, and improved by Abraham-Louis Breguet (1787), Peter Litherland (1791), Edward Massey (1800), and its modern ("table roller") form was developed by George Savage in the early 1800s. Since about 1900 virtually every mechanical watch, alarm clock and other portable timepiece has used the lever escapement.

The advantages of the lever are, first, that it is a "detached" escapement, it allows the balance wheel to swing completely free of the escapement during most of its oscillation, except when giving it a short impulse, improving timekeeping accuracy. Second, due to "locking" and "draw" its action is very precise. Third, it is self-starting, so if the watch is jarred in use so the balance wheel stops, it will start again. A cheaper and less accurate version of the lever escapement, called the pin pallet escapement, invented by Georges Frederic Roskopf in 1867, is used in clocks and timers.