|
In horology, a tourbillon (; "whirlwind") is an addition to the mechanics of a watch escapement. Developed around 1795 and patented by the French-Swiss watchmaker Abraham-Louis Breguet on June 26, 1801, a tourbillon aims to counter the effects of gravity by mounting the escapement and balance wheel in a rotating cage, to negate the effect of gravity when the timepiece (thus the escapement) is stuck in a certain position. By continuously rotating the entire balance wheel/escapement assembly at a slow rate (typically about one revolution per minute), positional errors are averaged out. Originally an attempt to improve accuracy, tourbillons are still included in some expensive modern watches as a novelty and demonstration of watchmaking virtuosity. The mechanism is usually exposed on the watch's face to show it off. ==Mechanics of the tourbillon== Gravity has a direct effect on the most delicate parts of the escapement, namely the pallet fork, balance wheel and hairspring. Most notably is the hairspring, which functions as the timing regulator for the escapement and is thus the part most sensitive to any exterior effects, such as magnetism, shocks, temperature, as well as inner effects such as pinning positions (inner collet), terminal curve, and heavy points on the balance wheel. Many inventions have been developed to counteract these problems. Temperature and magnetism problems have been eliminated with new materials. Shocks have much less effect today than at Breguet's time thanks to stronger and more resilient materials. The oscillator still gets disturbed at the moment of the shock, but the hairspring does not get as easily deformed from shocks as before, and so re-stabilizes itself quickly after such an event. Gravity comes into play on the remaining effects. One of them is easily taken away, namely heavy points on the balance wheel. This leaves pinning point and terminal curve. Both of these add a lot of variation to the regulation of a watch; assembly, regulation adjustments by the watchmaker, positioning in the watch, and later position changes by the owner. As the balance wheel goes from one extreme position to the other in its swing back and forth, the hairspring's coils extend and contract a great deal, leading to problems that are extremely hard to counteract. Some have tried using hairsprings that are cylindrical or even spherical instead of flat as is prominent today. Some variations of Breguet's overcoil have been developed to counteract the effects of the terminal curve. As for the pinning point, Grossmann, Berthoud, Breguet, Caspari and Leroy〔Reymondin, Charles-André et al., ''The Theory of Horology'', Switzerland: Swiss Federation of Technical Colleges (FET) () the Watchmakers of Switzerland Training and Educational Program Neuchâtel in collaboration with GREME, 1999 (2nd ed., 2005). ISBN 978-2-940025-12-1〕 tried many different possibilities, but not much improvement was gained. The biggest obstacle for a watchmaker regulating a watch, even today, is getting a similar result from the escapement no matter the position it is kept in. This has been made infinitely easier with accurate timing machines which give instantaneous timing results, whereas in Breguet's time all that watchmakers had was another watch to regulate from. So, results were not very exact and it could take weeks to get them. Effects of gravity on an escapement can have quite significant effects with slight variations of position. Even if a pocket watch was kept most of the time in a breast pocket, the exact position could still vary over 45°. A tourbillon quite neatly takes away this problem. The watchmaker now only needs to regulate for 3 different positions, instead of 6 as before. Those are two horizontal positions, dial up and down, and four vertical positions, crown at 12, 3, 6 and 9 o'clock. Even today with new materials and improved theories, it is impossible to regulate a mechanical watch so it keeps the same time in all positions. A tourbillon presents today's watchmakers the possibility of higher accuracy than conventional movements, although poising the balance well and ensuring that the balance spring expands and contracts symmetrically can achieve virtually the same result. A tourbillon most often makes one complete revolution per minute. This improves timekeeping in the 4 vertical positions because, even if a watch is stationary in a random vertical position, the tourbillon makes the escapement turn around its own axis, effectively ironing out the effects of gravity by turning the balance through all possible vertical positions during its rotation. A tourbillon has no effect in horizontal positions, since here the balance is horizontal and not affected by gravity as it turns. A tourbillon has no effect on the change in rate that accompanies a change in attitude from dial horizontal (dial up or down) to dial vertical (pendant up, down, left or right). This change in rate between horizontal and vertical is much greater than rate changes between different vertical positions. Breguet designed the tourbillon for pocket watches that are kept in a vertical position in the waistcoat pocket, and can be maintained in this vertical position overnight by hanging on a suitable stand, and in this vertical attitude a tourbillon is effective. However, the attitude of a wrist watch changes frequently from vertical to horizontal depending on what its wearer is doing. The effect of a tourbillon is small compared to the change in rate resulting from changes from vertical to horizontal, and vice versa. Inclined tourbillons such as those made by Greubel Forsey are an improvement in this regard. Mechanical watches today are mostly sold to buyers who value craftsmanship and aesthetics over very accurate timing. Most tourbillons use standard Swiss lever escapements, but some have a detent escapement. The tourbillon is considered to be one of the most challenging of watch mechanisms to make〔(【引用サイトリンク】 publisher = My Tourbillon )〕 (although technically not a complication itself) and is valued for its engineering and design principles. The first production tourbillon mechanism was produced by Breguet for Napoleon in one of his carriage clocks (travel clocks of the time were of considerable weight, typically weighing almost 200 pounds). 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「Tourbillon」の詳細全文を読む スポンサード リンク
|