Accutron
The first prototype mechanical tuning fork clock, the "pendule ç diapason", was manufactured by Louis F. Breguet, grandson of the famous Abraham-Louis Breguet. Louis Breguet filed the patent for this clock in France on October 26, 1866, and a supplement on March 13, 1867. An Irish watchmaker sold this watch in 1961 to the Firm Breguet in Paris, who sold it again a few years later to an unknown collector. Louis Breguet also introduced a clock with a vibrating blade and even mentioned a clock with two tuning forks and another one with two vibrating blades.
Bulova Accutron
The low frequency of the balance wheel made it impossible to improve the accuracy of the present mechanical watches. Therefore the Bulova Watch Company Switzerland, knowing that the American army was in need of a better time base for their instruments, asked the Swiss engineer Max Hetzel in 1952 to look into the possibility of the application of a higher frequency in a watch. Max Hetzel was born in Basle in 1921, graduated in 1946 at the Zurich Federal Polytechnic School as an electronic engineer, worked on TV and Communications and joined the Bulova Watch Company of Bienne, Switzerland, in 1948. This outstanding engineer was the first one to use an electronic device, a transistor in a wrist watch. Thus, Max Hetzel developed the first watch in the world that truly deserved the qualification "electronic": the world-famous "Bulova Accutron".
- 1953 Max Hetzel receives the first useful transistors, the
"CK 722", from RaythonUSA and produces his first working model by hand. The
length of thetuning fork was five centimeters. The patent application is filed
inSwitzerland on June 19th 1953 under no. 312290.
- 1954 The ATO electronic pendulum clock is shown at the CIC
in Paris, the firstclock in the world with a transistor and without electrical contacts.In
June, the first useful batteries suitable for watches, invented by Mallory,become
available.In November, the first prototype wristwatch is made to function.
- 1955 Eight watch-sized models are produced in Bienne. In
Switzerland manydoubted whether "The Accutron" would become successful.
- 1956 The president of the Bulova Watch Co. in New York,
Arde Bulova, and hisengineers become enthusiastic about the tuning fork system.
- 1959 Max Hetzel goes to New York with his family and
becomes Chief Physicistat the headquarters in Jackson Heigts, New York. The Bulova
Accutron isdeveloped by team work of two scientists: Max Hetzel and William O. Bennett.The
start of the production-engineering phase takes off.
- 1960 On October 10th, the new president of the Bulova
Watch Co., Omar N. Bradley, ex-chief of staff of General D. Eisenhower and known for
hisparticipation in the Normandy Offensive, announces the Bulova Accutroncaliber 214, the
first electronic watch in the world. Cased in steel, gold orplatinum, the number of parts
had been dramatically reduced to a mere 27of which only 12 were moving parts. By
comparison, a selfwinding watch atthat time contained about 136 parts, 26 of them
moving.The sale of the Accutron starts on October 25th.
- 1964 The "Bulova Accutron" is chosen to be
buried for a time period of 5000 yearson the grounds of the New York World Fair in order
to save it for futuregenerations as an example of one of the 44 most innovative objects to
beinvented during the last two and a half decades.
- 1964-1970 In different trips into space with the
"Explorer" and the "Apollo", the "BulovaAccutron" is used by
astronauts with full satisfaction.
- 1966 The first tuning fork wrist watches are registered at
the Observatory ofNeuchâtel by Ebauches S.A. and by C.E.H. of Neuchâtel.
- 1973 At this time four million "Bulova
Accutrons" have been sold sinceproduction started.
Description of the Accutron.
The "Bulova Accutron" has a frequency of 360 oscillations per second (360 Hz). The vibration of the tuning fork is controlled by a transistorised circuit in the following way: When the left magnet on the tuning fork moves to the right, the phase-sensing coil generates an induction voltage on the base of the transistor. The transistor "switches on", becomes a conductor instead of a resistor and the electrical current is able to start flowing through the right circuit. The drive-coil becomes a magnet and gives an impulse to the permanent magnet. The movement of the permanent magnet in the driving-coil also causes an induction voltage opposing the power cell voltage. The result is a very small electric current and a prolongued battery life. The problem of turning the linear motion of the fork into a circular motion of the hands is solved in the following way: the index jewel is connected to the fork and pushes the ratchet wheel one tooth forward, the pawl jewel is fixed to the watch frame and prevents the ratchet wheel from revolving backwards. The ratchet wheel was an outstanding technical achievement: 2.4 mm in diameter, 0.04 mm thick and 300 teeth, each 1/100 mm high. In one year it revolves 38 milion times. To protect the ratchet system, the Accutron may be set only by turning the hands in a forward direction. Another technical hallmark were the coils: the driving coil has 8,000 turns made of wire with a diameter of 0.015 mm and an incredible length of about 90 meters.
They are inherently more accurate than balance wheel watches for a number of reasons.The accuracy of a traditional balance wheel watch is dependant on many factors. Friction in the pivots (bearings) due to changes in the quality of the lubricating oil play a significant part in the ability of a mechanical watch to maintain accuracy and consistency of rate. Also, the condition of the mainspring and gear train driving it is very important. The rate of Tuning Fork watches is affected much less by lubrication, though it is still necessary for the correct functioning of the watch.
The other major factors affecting accuracy of any mechanical watch are temperature changes and errors due to position (i.e. how gravity effects it's operation in different orientations). Tuning fork watches are inherently far less affected by these problems. The fork has no bearings. It is far easier to "build in" temperature compensation into a Tuning Fork than into a circular balance wheel and it's hairspring.
Gravity affects Bulova tuning forks in only 2 orientations (tines up and tines down) compared with the usual 5 positions of good quality balance wheel watches. (Dial up, dial down, winder up, winder right, winder left). The tuning forks of the ESA movements have virtually zero positional error.A balance wheel vibrates at usually 2 1/2 times a second, whereas the tuning fork hums at 300-720 times a second, depending on the model. Modern mechanical watches vibrate as fast as 5 times a second, in an attempt to improve their accuracy by making the balance wheel lower in mass and size, thus reducing their susceptibility to external influences.
Only Watchmakers of the highest skill can adjust a balance wheel watch for its best possible performance under all conditions. Repairing and adjusting tuning fork watches is considerably easier, as there are no adjustments apart from the index mechanism, which converts the vibrations of the tuning fork into rotary motion. Of course, skill and experience is still needed to adjust the index mechanism correctly.
Another interesting difference between Tuning Fork watches and Balance Wheel watches is the flow of mechanical power in the mechanism. A traditional watch has a mainspring, which stores the energy to drive the gears. This energy starts off strong at the mainspring and is slowly diminished in torque through the train of gears until it is suitable for use by the balance wheel. How much loss of energy occurs in this process is again a function of the quality of the bearings and the state of lubrication. The accuracy of the conventional watch is strongly dependant on the constancy of the power that finally arrives at the balance wheel. In a Tuning Fork watch the power flow is the other way around. The fork drives the gear train, as opposed to a balance that is driven by the gear train. The forces on the gear train of the tuning fork watch are far less, and the quality of the bearings and lubrication are of much less consequence to its accuracy than is typical for a balance-wheel watch. Nevertheless, they are still susceptible to problems due to dirt and poor lubrication as any precision mechanical item is, and maintenance of an Accutron is often overlooked because of their inherent accuracy and reliability. If maintained correctly, they could be expected to last a long time, as the forces on the bearings are so small
In summary, we can see that the gear train of a conventional watch performs two functions: it drives the hands and transmits power to the balance wheel. In a tuning fork watch, it only drives the hands.The Electronics of the Tuning Fork WatchThe tuning fork is kept vibrating by an electronic circuit, powered by a battery. While the electronics required to do this are not considered remarkable by today's standards of modern electronics, when taken in historical perspective it is a different story.
When the Accutron was first released, not only was it the first watch to be controlled by a transistor, it was one of the first consumer items of any kind to use this device. Up till then, all battery-powered watches had a balance wheel and hairspring that operated a small set of contacts. These mechanical contacts momentarily supplied electrical current to a coil that in turn gave a magnetic impulse to the balance, keeping it moving. The transistor itself was still in its infancy, hardly even heard of by the general public, who considered it a novelty of scientific interest only. So it was remarkable not only to use such a device in a consumer item, but also to achieve standards of miniaturization previously unheard of.
Remember in those days, nearly all electronic devices, such as radios and TV's were based on vacuum tubes