46TECHNIQUESTE
The tuning-fork watch:
humming along for 50 years
The presentation of the first electro-mechanical
watches by Eglin and LIP in 1952 was of deep concern to Arde Bulova, managing director of the
Bulova Watch Company in New York. Was he
about to fall victim to a technological revolution?
Bulova took a plane to Switzerland and went to his
factory in Biel, where he’d been manufacturing
watch movements since the 1920s. There he met
Max Hetzel, a young electrical engineer, and asked
him to draw up a detailed report on the new electric movements. Hetzel submitted his findings in
April 1952. He concluded that these watches were
not really sensational ; their only real advantages
were that they got rid of the spring-driven motor,
and the battery kept the watch going for a year.
Max Hetzel, father of the tuning-fork watch.
Birth of the Accutron. Hetzel then revealed that
he could, in principle, construct something far better : a high-frequency movement regulated by a
vibrating tuning-fork controlled by the novel transistor. The idea was based on his diploma thesis at
46
|
watch around no 010 autumn 2010 - winter 2011
Lucien F.
Trueb
ECHNIQUESTECHN
Hetzel’s 1953 patent was virtually impossible to circumvent.
the Swiss Federal Institute of Technology in Zurich,
the subject of which happened to be electronic tuning-fork oscillators.
Bulova gave the mandate to Hetzel who in 1953
filed a practically all-encompassing patent covering the tuning-fork watch. The fork, with each prong
bearing a nickel-cobalt permanent magnet surrounded by a static coil, is made to vibrate at a
steady frequency by a simple transistorised circuit.
A single source of power and frequency. The
tuning fork also drives the movement of the watch.
At each vibration, a tiny prismatic ruby at the end of
a metal strip attached to one of the prongs
advances a 2.4 mm-diameter wheel tooth by tooth.
This in turn drives the train of gears that moves the
hands around the dial. A mercury battery gave the
watch a running time of a year. The rate was stable
to within two seconds a day, which was adequate
but hardly revolutionary for the time, since mechanical movements with high balance frequencies of
36,000 v/h had already achieved this performance.
Hetzel built eight 30 mm-diameter prototype movements, which were enough for the formidable Lore
Sandoz-Peter, Bulova’s managing director in Biel
at the time. The project was then transferred to
Bulova’s laboratory at Jackson Heights near New
York. This upset Hetzel, who started looking for a
new job. But Bulova couldn’t afford to lose such an
outstanding engineer, so Hetzel was offered the
post of chief physicist at Jackson Heights, which
he readily accepted. He thus got the chance to get
his movement ready for production.
On October 25, 1960, Omar N. Bradley, former
chief-of-staff to General Eisenhower during World
War II, launched the tuning-fork watch. It was
called the Accutron, derived from accuracy and
electronics, and its calibre 214 movement had only
27 parts, 12 of them mobile. It was a major event
as the first watch without a balance-wheel regulator, and its transistor made it the first truly electronic watch in series production.
47
watch around no 010 autumn 2010 - winter 2011 |
TECHNIQUESTECH
The launch of the first wristwatch without a balance and spring was a major event.
Swissonics and Megasonics. Once the Accutron
had been launched on the market, Hetzel returned
to Switzerland where he was recruited in 1963 by the
Centre for Electronic Horology (CEH) in Neuchâtel.
There he developed the Swissonic, a variant of the
tuning-fork watch with the oscillator configured as a
horseshoe around the movement. The initial series
was scheduled to go into production in a pilot plant
managed by Hetzel in Gals near the town of Marin in
Canton Neuchâtel. But the project collapsed when
the Swissonic design turned out to infringe the
Bulova patent.
In 1969 Hetzel joined Omega, who hired him to circumvent his own patent of 1953. To this end he
developed a most original oscillating motor. It consists of an asymmetrical turning fork vibrating at
720 Hz. One prong of the fork carries a sealed, oilfilled box containing a 1.2 mm-diameter ratchet
wheel with 180 teeth. The wheel vibrates between
two sprung rubies that ensure it turns in one direction. The rotation of the wheel in the box is
48
|
watch around no 010 autumn 2010 - winter 2011
HNIQUESTECHNIQ
Accutron’s anniversary model with a tuning-fork movement, and Bulova’s Champlain Black, fitted with the latest-generation quartz movement vibrating at eight times the frequency of its rivals.
transmitted magnetically to the gear train using
platinum-cobalt magnets.
Omega filed 12 patents to protect this invention before
presenting it in 1973 as the Megasonic. The new
micro-motor was nicknamed the “mouse”. Sadly the
reliability of the Megasonic movement (Omega calibres 1220 and 1230) left much to be desired, as the
magnetic transmission proved too weak. Production
went to some 10,000 watches before the Megasonic
was abandoned in 1976 in the face of the prodigious
ascent of the quartz movement.
Under licence by Ebauches and Citizen. Working
completely independently from the CEH and Bulova,
engineers at the Ebauches company in Neuchâtel had
come out with a new version of the tuning fork movement in 1961. Called the Mosaba (montre sans balancier – watch without a balance), the movement was
fitted with a tri-dimensional 300 Hz oscillator that had
no positional errors. Unfortunately, this reliable movement too infringed the Bulova patent, but Ebauches
paid a million dollars for the licence to produce it. The
Mosaba was introduced in 1967 as the Swissonic 100
and launched on the market two years later. There was
even a chronograph version.
Meanwhile back in the USSR, Moscow’s Watch
Factory no 1 started selling illegal copies of the
Accutron calibre 214 from 1968 under the name of
Kamertoni. Citizen in Japan, on the other hand,
went into a joint venture with Bulova in the late sixties to manufacture and sell tuning-fork watches
in Asia. The first were introduced in 1972 as
the HiSonic.
Five years later the quartz wristwatch had become
established and production of the tuning-fork
movement halted everywhere. During its 17-year
product life, Bulova sold between four and five million Accutrons. Citizen Watch produced another
million HiSonics, while Ebauches put several hundred thousand Mosaba-Swissonic movements on
the market. The Soviets never published the production figures for the Kamertoni calibre.
•
49
watch around no 010 autumn 2010 - winter 2011 |
50TECHNIQUESTE
Capturing the moon on a dial
The traditional moon in the Chronoswiss dial is flanked by Chopard’s display of both hemispheres, good for 122 years
(left), while the Lange & Söhne moon (right) will need correcting 10 and a half centuries from now.
Timm Delfs
Among the planets that have at least one satellite,
the Earth is the closest to the sun. Our sun-side
neighbours, Venus and Mercury, have no moon
while the Earth and all the planets beyond it have
one or several. Orbiting the Earth in regular cycles
and forever changing shape according to its position, our Moon has forever fascinated humanity.
Since it can look as big as the sun and can even
blot it out during an eclipse, the Moon has assumed
an importance equal to that of our daytime star.
The rhythm of the different phases from one new
moon to the next gave us the division of the year
into months, and to the Moon is dedicated the first
day of the week.
But just like the day and the year, the Moon’s month
has always proved awkward for calendar compilers.
The three units of time are not bound to one another
by simple arithmetical ratios. The year doesn’t last
365 days, but 5 hours, 49 minutes and 12 seconds
longer – almost a quarter of a day. That is why we
add a day to the year every four years. The synodic
month, the time taken for the Moon to go once
around the Earth and back to the same position relative to the sun, is on average 29 days, 12 hours,
44 minutes and 2.8 seconds. But these are mean
periods that can vary under the influence of other
50
|
watch around no 010 autumn 2010 - winter 2011
heavenly bodies. Astronomers have long wrestled
with the problem, and watchmakers even more so.
Nice, but not that useful. We might not find much
practical use for it, but an indication of the moonphases on the dial does give a watch extra appeal.
The fascination with Earth’s satellite remains undiminished in a world ruled by technology. The most
widespread way of representing the moonphases in
a watch is by a disc having two moons against a
starry background which goes round once in the
period of two lunations. An opening in the dial
reveals each moon in turn, the other being masked.
When the moon is not full, it is partially masked by
two semicircular lunar terminators leaving the visible portion of the moon to indicate its phase. In the
simplest mechanisms, the moons disc has 59 teeth.
A 24-hour wheel advances the disc once a day by
one tooth. The disc thus completes a revolution in
59 days. Divided by two, this gives a lunation of
29 days and 12 hours – 44 minutes and 2.8 seconds short of the real lunation. A whole day of error
accumulates every three years, and the moonphase indicator has to be reset manually.
This crude approximation is naturally unworthy of a
perpetual-calendar watch. Fortunately it can be
TECHNIQUESTECH
The perpetual moon by H. Moser will show an error of a day in 1,027 years; the Bulgari/Daniel Roth moon is a miniature
painting, while that of De Bethune is a sphere.
improved with an additional wheel. Instead of acting
directly on the disc, the 24-hour wheel advances a
seven-pointed star once a day, which completes a revolution in a week. The star is fitted with a 16-tooth
wheel that meshes with a 135-tooth moons disc. In
that way you achieve a lunation of 29 days, 12 hours
and 45 minutes, a much smaller discrepancy that
accumulates one day of error against the real moon in
122 years and 46 days. But the additional wheel
makes the moons disc turn the wrong way, so yet
another gear-wheel is needed to reverse its direction.
This is the solution described in watchmaking manuals and followed in one way or another by the majority
of watch makes, which call the indication “precise
moonphases” or “the astronomical moon”. Further calculation can nevertheless improve this result.
H. Moser & Co’s Perpetual Moon has reached such
a level of precision that it takes 1,027 years to diverge
a single day from the real Moon, while the Lange 1815
Moonphase needs to be reset only after 1,058 years.
The moon’s moods. For the benefit of those who
brook no imprecision, here are some other characteristics of our Moon. The 29 days, 12 hours,
44 minutes and 2.8 is only the average period of
a lunation. In fact it can vary as much as 44 seconds depending on whether the Moon is at its
apogee (farthest from Earth) or at its perigee (closest to Earth). Because a lunation takes longer than
29 days, the full moon at its maximum is not always
visible every time from the same point on Earth.
This privileged viewpoint shifts 191° westwards at
each full moon. Furthermore, the Moon goes more
than 360° degrees around the Earth during a lunation. From one full moon to the next it travels about
390°. To complete a 360° orbit of the Earth, it only
needs 27 days, 7 hours, 43 minutes and 12 seconds. Astronomers call this period the sidereal
month, because it corresponds to what one would
observe from a fixed point outside the solar system
such as a star.
•
51
watch around no 010 autumn 2010 - winter 2011 |