Deadbeat escapement Anchor escapement

deadbeat escapement, showing: (a) escape wheel, (b) pallets showing concentric locking faces, (c) crutch.



animation showing deadbeat escapement in motion. (click activate)

the above 2 disadvantages removed invention of improved version of anchor escapement: deadbeat or graham escapement. erroneously credited english clockmaker george graham introduced around 1715 in precision regulator clocks. invented around 1675 astronomer richard towneley, , first used graham s mentor thomas tompion in clock built sir jonas moore, , in 2 precision regulators made new greenwich observatory in 1676, mentioned in correspondence between astronomer royal john flamsteed , towneley

the deadbeat form of anchor escapement less tolerant of inaccuracy in manufacture or wear during operation , used in precision clocks, use spread during 19th century quality pendulum clocks. pendulum clocks made today use it.

tower clocks 1 of few types of pendulum clock anchor escapement did not dominate. varying force applied wheel train large exterior hands, exposed wind, snow, , ice loads, better handled gravity escapements.

how works

the deadbeat escapement has 2 faces pallets, locking or dead face, curved surface concentric axis on anchor rotates, , sloping impulse face. when escape wheel tooth resting against 1 of dead faces, force directed through anchor s pivot axis, gives no impulse pendulum, allowing swing freely. when pallet on other side releases escape wheel, tooth lands on dead face first, , remains resting against of pendulum s outward swing , return. period escape wheel locked , unable turn. near bottom of pendulum s swing tooth slides off dead face onto slanted impulse face of pallet, allowing escape wheel turn , give pendulum push, before dropping off pallet. still frictional rest escapement because sliding of escape tooth on dead face adds friction pendulum s swing, has less friction recoil escapement because there no recoil force.

in contrast backward slant of anchor escape wheel teeth, deadbeat escape wheel teeth radial or slant forward ensure tooth makes contact dead face of pallet, preventing recoil.

the airy condition

in 1826 british astronomer george airy proved pendulum driven drive impulse symmetrical bottom equilibrium position isochronous different drive forces, ignoring friction, , deadbeat escapement approximately satisfies condition. satisfied if escape wheel teeth made fall on corner between 2 pallet faces, escapement operate reliably teeth must made fall above corner, on dead face.