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Lesson 4
-- Structure & Theory 26 Nov 2006
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There are 4 main parts for a clock or a watch.
- Power
- Wheel Train
- Escapement
- Display
In this lesson, we still use the clock as an example,
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| 1. Power |
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The brass gear is called Mainwheel.
The long thin metal strip is called Mainspring.
The amount of energy can be stored mostly depends on
the elasticity (material, e.g. steel) and the effectinve
length of the mainspring.
Most watches have about 50 hours power and some expensive
watches have 8 or more days power.
e.g. Jaeger-LeCoultre Master 8 Days (aboutUS$16000)
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| 2. Wheel Train |
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The wheel train include gear 2, 3, 4.
There are two functions for the wheel train.
- Transfer the power from the Mainwheel to the Balance
Wheel. When the energy goes through the wheel train,
the high torque form the Mainwheel will become the
high speed oscillation at theBalance Wheel.
- Calculate the time according to the gear ratio between
each wheel.
- Gear 2 -- Minute
- Gear 4 -- Second
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| 3. Escapement |
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Escape wheel, Pallet Fork, Balance Spring and Balance
wheel form the ESCAPEMENT
which controls the time of a clock.
Balance Spring oscillates and Balance Wheel swings
as a result they divide the time.
Anchor and escape wheel control the power release according
to the "divided time".
There are different types of balance wheels, I will
introduce them later.
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| 4. Display |
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Show you the time ! |
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| How to calculate
the time with the gears |
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1 perod = the yellow dot goes from left to right and
back to left.
Frequency = 1 / Time for one period
There are 4 main frequencies for the balance wheel
in a watch.
- 18000 per hour
- 21600 per hour
- 28800 per hour
- 36000 per hour
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A : Pallet Fork
Pay attention to the two pins (red
rectangles)on the Pallet Fork in the following
movie.
B: Balance wheel
5: Escape wheel
I put some pigments on the parts for movie recording
only, the weight of the pigment will affect the frequency
of the balance spring, as a result, affect the accuracy
of the time.
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When the balance wheel swings, it will control the
Pallet Fork to lock or release the escape wheel.
Play back speed is reduced for easy viewing.
If you cannot see the movie in the browser, please
download it.
Download Movie
WMV 2.3M
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The frequency of the balance wheel can be calculated from
the formula:
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For the clock in lesson
3
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Tp(escape wheel)
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15
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Ta(escape wheel)
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8
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Tp(4th)
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60
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Ta(4th)
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6
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Tp(3rd)
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36
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Ta(3rd)
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7
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Tp(2nd)
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70
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Ta(2nd)
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10
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Frequency = ( 70 x 36 x 60 x 15 x
2 ) / ( 7 x 6 x 8 ) = 13500
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The gear ratio for the wheel train should be:
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Because the gear ratio cannot be changed, the accuracy of
a clock or a watch can only be adjusted by the frequency of
the balance wheel.
The frequency of the balance wheel can be changed by adjusting
the effective length of the balance spring.
Longer the effective length = lower the frequency
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Effective lenght of the balance spring =
B to C |
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