|
A micrometer ( ), sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for precise measurement of components〔Encyclopedia Americana (1988) "Micrometer" Encyclopedia Americana 19: 500 ISBN 0-7172-0119-8 (set)〕 in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers. Micrometers are usually, but not always, in the form of calipers (opposing ends joined by a frame), which is why micrometer caliper is another common name. The spindle is a very accurately machined screw and the object to be measured is placed between the spindle and the anvil. The spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and the anvil. Micrometers are also used in telescopes or microscopes to measure the apparent diameter of celestial bodies or microscopic objects. The micrometer used with a telescope was invented about 1638 by William Gascoigne, an English astronomer. Colloquially the word ''micrometer'' is often shortened to mike or mic () (). ==History of the device and its name== The word ''micrometer'' is a neoclassical coinage . The ''Merriam-Webster Collegiate Dictionary'' says that English got it from French and that its first known appearance in English writing was in 1670. Neither the metre nor the micrometre (µm) nor the micrometer (device) as we know them today existed at that time. However, the people of that time did have much need for, and interest in, the ability to measure small things and small differences. The word was no doubt coined in reference to this endeavor, even if it did not refer specifically to its present-day senses. The first ever micrometric screw was invented by William Gascoigne in the 17th century, as an enhancement of the vernier; it was used in a telescope to measure angular distances between stars and the relative sizes of celestial objects. Henry Maudslay built a bench micrometer in the early 19th century that was jocularly nicknamed "the Lord Chancellor" among his staff because it was the final judge on measurement accuracy and precision in the firm's work. In 1844 details of Whitworth's workshop micrometer were published.〔"Whitworth's workshop micrometer", The Practical Mechanic and Engineer's magazine, Nov 1844, pp43-44〕 This was described as having a strong frame of cast iron, the opposite ends of which were two highly finished steel cylinders, which traversed longitudinally by action of screws. The ends of the cylinders where they met was of hemispherical shape. One screw was fitted with a wheel graduated to measure to the ten thousandth of an inch. His object was ''to furnish ordinary mechanics with an instrument which, while it afforded very accurate indications, was yet not very liable to be deranged by the rough handling of the workshop''. The first documented development of handheld micrometer-screw calipers was by Jean Laurent Palmer of Paris in 1848;〔(Roe 1916:212. )〕 the device is therefore often called ''palmer'' in French, and ''tornillo de Palmer'' ("Palmer screw") in Spanish. (Those languages also use the ''micrometer'' cognates: ''micromètre, micrómetro''.) The micrometer caliper was introduced to the mass market in anglophone countries by Brown & Sharpe in 1867,〔(Roe 1916:210-213, 215. )〕 allowing the penetration of the instrument's use into the average machine shop. Brown & Sharpe were inspired by several earlier devices, one of them being Palmer's design. In 1888 Edward W. Morley added to the precision of micrometric measurements and proved their accuracy in a complex series of experiments. The culture of toolroom accuracy and precision, which started with interchangeability pioneers including Gribeauval, Tousard, North, Hall, Whitney, and Colt, and continued through leaders such as Maudslay, Palmer, Whitworth, Brown, Sharpe, Pratt, Whitney, Leland, and others, grew during the Machine Age to become an important part of combining applied science with technology. Beginning in the early 20th century, one could no longer truly master tool and die making, machine tool building, or engineering without some knowledge of the science of metrology, as well as the sciences of chemistry and physics (for metallurgy, kinematics/dynamics, and quality). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「micrometer」の詳細全文を読む スポンサード リンク
|