Comparison of Motion in Anchor and Deadbeat
A major cause of error in clocks is changes in the drive force applied to the escapement, caused by small changes in the friction of the gears or the pallets, or the diminishing force of the mainspring as it unwinds. An escapement in which changes in drive force do not affect the rate is called isochronous. The superior performance of the deadbeat over the anchor is caused by its improved isochronism. This is due to the different ways changes in drive force affect the swing of the pendulum in the two escapements:
- In the anchor escapement, an increase of drive force causes the pendulum to swing back and forth more quickly, but does not increase the pendulum's amplitude, the length of its swing, much. The increased force of the escape wheel tooth on the pallet during the recoil part of the cycle tends to decrease the pendulum's swing, while the force of the tooth during the forward impulse part of the cycle tends to increase the pendulum's swing. These tend to cancel each other out, leaving the swing unchanged. But both these effects decrease the time of swing. In other words, increased force knocks the pendulum back and forth in a fixed arc faster.
- In the deadbeat escapement, increased drive force does not change the period of the pendulum much, resulting in better isochronism and better timekeeping, but it does increase the pendulum's swing. Since the escapement doesn't have a recoil period when the tooth's force opposes the direction of the pendulum's motion, increased force causes the pendulum to swing in a wider arc, as well as move faster. The time required to cover the extra distance exactly compensates for the increased speed of the pendulum, leaving the period of swing unchanged. Although the wider swing causes a slight increase in period due to circular error, for the small amplitudes used in clocks this effect is negligible.
When the deadbeat was invented, clockmakers initially believed it had inferior isochronism to the anchor, because of the greater effect of changes in force on the pendulum's amplitude.
Read more about this topic: Anchor Escapement
Famous quotes containing the words comparison of, comparison, motion and/or anchor:
“When we reflect on our past sentiments and affections, our thought is a faithful mirror, and copies its objects truly; but the colours which it employs are faint and dull, in comparison of those in which our original perceptions were clothed.”
—David Hume (1711–1776)
“The comparison between Coleridge and Johnson is obvious in so far as each held sway chiefly by the power of his tongue. The difference between their methods is so marked that it is tempting, but also unnecessary, to judge one to be inferior to the other. Johnson was robust, combative, and concrete; Coleridge was the opposite. The contrast was perhaps in his mind when he said of Johnson: “his bow-wow manner must have had a good deal to do with the effect produced.””
—Virginia Woolf (1882–1941)
“It is the fixed that horrifies us, the fixed that assails us with the tremendous force of mindlessness. The fixed is a Mason jar, and we can’t beat it open. ...The fixed is a world without fire--dead flint, dead tinder, and nowhere a spark. It is motion without direction, force without power, the aimless procession of caterpillars round the rim of a vase, and I hate it because at any moment I myself might step to that charmed and glistening thread.”
—Annie Dillard (b. 1945)
“The daughter of debate, that eke discord doth sow,
Shall reap no gain where former rule hath taught still peace to
grow.
No foreign banished wight shall anchor in this port;
Our realm it brooks no stranger’s force, let them elsewhere resort.”
—Elizabeth I (1533–1603)