Friday, August 6, 2010

TOURBILLON WATCHES VS OPEN HEART WATCHES

Tourbillon Watches


18th century tourbillon by Bréguet

In horology, a tourbillon (pronounced /tʊərˈbɪljən/, French: [tuʁbijɔ̃], "whirlwind") is an addition to the mechanics of a watch escapement. Developed around 1795 by the French - Swiss watchmaker Abraham-Louis Breguet from an earlier idea by the English chronometer maker John Arnold a tourbillon counters the effects of gravity by mounting the escapement and balance wheel in a rotating cage, ostensibly in order to negate the effect of gravity when the timepiece (and thus the escapement) is rotated. 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.

The Tourbillon

The Tourbillon is one of the most complex and difficult to make watch escapements. As such it is usually a mark of high quality workmanship and tourbillon watches often fetch high prices in auction houses and at the luxury end of the watch market.

What is a Tourbillon?

The tourbillon is a form of escapement for wristwatches or pocket watches. Some clocks have also been built with tourbillon escapements, even there is little reason for them.

The motive behind the tourbillon was simple: people don't stand still! To obtain maximum accuracy from a timepiece it essential that the movement of the oscillator must be isochronal - that is, it must keep regular and predictable time.

Unfortunately this is difficult to achieve when the wearer of the watch insists on moving the wrist around. Such movements cause the stresses and friction on the watch mechanism to vary, along with the influence of gravity.

A watch that tells perfect time when held at one angle might not do so at another. With clocks this is not a problem - since a clock is always in the same position, it is possible to adjust for any error. With a constantly moving wristwatch the error is itself constantly changing.

Mechanism of Action


A tourbillon assembly

Gravity was thought to have a very adverse effect on the accuracy of time pieces at the time of the invention of the tourbillon, particularly because pocket watches were often less accurate than stationary clocks of the same construction. The prevailing theory amongst horologists of the time was that pocket watches suffered from the effects of gravity since they were usually carried in the same pocketed position for most of the day, which was vertical, and then held in a different position while being read. Because the movement of pocket watches and similar pieces were oriented with respect to the cases and the dials, their movements were positioned with the axes of motion perpendicular to their faces. This meant that when the timepiece was placed vertically, the axis of motion of the movements would be parallel to the ground, and thus to the force of gravity. In such a position, the force of gravity would affect the motion of parts of the movement differently when the parts were in different positions (i.e., moving with gravity or moving against it), which would cause variations in the rate of the movement, which in turn would affect the timepieces' accuracy. If adjusted for one position, the rate would change when the piece was kept in a different position, such as when being held to be read or when placed on a table at night. In a tourbillon, the entire escapement assembly rotates, including the balance wheel, the escape wheel, the hairspring, and the pallet fork, in order to average out the effect of gravity in the different positions. The rate of rotation varies per design but has generally become standardized at one rotation per minute. Most tourbillons use standard swiss lever escapement, but some have a detent escapement, and others contain novel designs, such as the Audemars Piguet Millenary for example.

The tourbillon is considered to be one of the most challenging of watch mechanisms to make (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).

Double-axis tourbillon


Cutout of a double-axis tourbillon pocketwatch
In 2003, inspired by the double axis tourbillon invented in the 1970's by Richard Good (see below), the young German watchmaker Thomas Prescher developed for the Thomas Prescher Haute Horlogerie the first flying double-axis tourbillon in a pocket watch and, in 2004, the first flying double-axis tourbillon with constant force in the carriage in a wristwatch. Shown at the Baselworld 2003 and 2004 in Basel, Switzerland.

A characteristic of this tourbillon is that it turns around two axes, both of which rotate once per minute. The whole tourbillon is powered by a special constant-force mechanism, called a remontoire. Thomas Prescher invented the constant-force mechanism to equalize the effects of a wound and unwound mainspring, friction, and gravitation. Thereby even force is always supplied to the oscillation regulating system of the double-axis tourbillon. The device incorporates a modified system after a design by Henri Jeanneret.

Double and Quadruple tourbillons

Robert Greubel and Stephen Forsey launched the brand Greubel Forsey[2] in 2004 with the introduction of their Double Tourbillon 30° (DT30). Both men had been working together since 1992 at Renaud & Papi, where they developed complicated watch movements. The Double Tourbillon 30° features one tourbillon carriage rotating once per minute and inclined at 30°, inside another carriage which is rotating every four minutes.

In 2005 Greubel Forsey presented their Quadruple Tourbillon à Différentiel (QDT),which uses two double-tourbillons working independently. A spherical differential connects the four rotating carriages, distributing torque between two wheels rotating at different speeds.

Triple-axis tourbillon


Triple-Axis-Tourbillon Regulator Sport

In 2004 Thomas Prescher developed the first triple-axis tourbillon for the Thomas Prescher Haute Horlogerie with constant force in the carriage in a wristwatch. Presented at the Baselworld 2004 in Basel, Switzerland, in a set of three watches including a single-axis, a double-axis, and a triple-axis tourbillon.

The world's unique tri-axial tourbillon movement for wristwatch with traditional jewel bearings only was invented by the independent watchmaker Aaron Becsei - Bexei Watches in 2007. The wristwatch PRIMUS was presented at the Baselworld 2008 in Basel, Switzerland. In the three axis tourbillion movement the 3rd (external) cage has a unique form which provides the possibility of using jewel bearings everywhere - instead of ball-bearings. This is a unique solution at this size and level of complication.

Modern tourbillon watches

In modern mechanical watch designs, a tourbillon is not required to produce a highly accurate timepiece; there is even debate amongst horologists as to whether tourbillons ever improved the accuracy of mechanical time pieces, even when they were first introduced, or whether the time pieces of the day were inherently inaccurate due to design and manufacturing techniques. Nevertheless, the tourbillon is one of the most valued features of collectors' watches and premium timepieces (Ref. August 2006 WatchTime article Girard-Perregaux's Tourbillon Icon), possibly for the same reason that mechanical watches fetch a much higher price than similar quartz watches that are much more accurate. High-quality tourbillon wristwatches, which are usually made by the Swiss luxury watch industry, are very expensive, and typically retail for at least thousands of dollars or euros, with much higher prices in the tens of thousands of dollars/euros being common. A recent renaissance of interest in tourbillons has been met by the industry with increased availability of time pieces bearing the feature, with the result that prices for basic tourbillon models have receded somewhat in recent years (where as previously they were very rare, in either antiques or new merchandise); however, any time piece that has a tourbillon will cost a great deal more than an equivalent piece without the feature.

Modern implementations typically allow the tourbillon to be seen through a window in the watch face. In addition to enhancing the charm of the piece, the tourbillon can act as a second hand for some watches as it generally rotates once per minute. However some Tourbillons spin faster (Gruebel Forsey's 24-second tourbillon for example.). There are many "Tourbillon" fake/replicas of premium brand watches that emulate this feature with the oscillating balance wheel visible through the watch dial; however, these are not tourbillons. This feature is often referred to as "open heart".

In the late 20th century, the first research into multi-axis tourbillion movements was done by British clock makers Anthony Randall and Richard Good, eventually producing two and three-axis tourbillon movements.

Affordability crisis

Several Chinese manufacturers now produce a variety of tourbillon movements. These movements are bought as Ebauches by some foreign manufacturers such as Cecil Purnell and incorporated into watches that meet the requirements of the Federation of the Swiss Watch Industry to be sold as Swiss watches. The availability of cheap tourbillons has led industry spectators to worry that another "Quartz Crisis" may occur, where the Swiss watch industry will not be able to adapt quickly to cheaper complicated mechanical watches produced in other countries.

Source : Wikipedia

Open Heart Watches

Open heart watches only display the rotating mechanism of balance wheel. There is no effects of gravity on the escapement and balance wheel. The price of these watches are not expensive compared to the tourbillon.

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