Vincent Lee

WRIT 340

Instructor: Dr. Ramsey

Bio: Vincent Lee is a sophomore majoring in electrical engineering. He likes to entertain other people with weird facts and trivia. He is also adventurous with a curious mind. Abstract: With the invention of digital watches, automatic watches started off as a practical tool, and are now an artistic jewelry. Their complex engineering solution to keeping accurate time without electronics has been regarded as a watch that is unnecessarily brilliant. This contributes to its high price, as well as its low quantities. Automatic watches have a longer shelf-life than digital watches and requires no batteries making them environmentally friendly. Their design is, in fact, based on the laws of energy conservation, a simple physics concept that is prevalent in many applications we use today. The advancement in technology allows modern automatic watches to form into a new watch that is now a combination of both its high quality engineering precision as well as its expert craftsmanship.

Keywords: mechanical engineering, lifestyle, art, physics

Multimedia Suggestions: watch movements of the mainspring inside an automatic watch, animation of the overall physics process of an automatic watch

A Timeless Instrument: How Automatic Watches Work

Introduction

You see them everywhere. Automatic watches are advertised in jewelry stores and fashion

magazines, and yet, some people do not understand what exactly it is. In short, an automatic watch is

a mechanical watch that powers itself, hence “automatic”. The meticulous arrangements of simple

mechanical parts used to keep time are so special that Rolex, Patek-Phillipe, and Omega, several

popular brands in the watchmaking industry, continue to craft automatic watches. The efforts in

engineering an automatic watch require highly skilled watchmakers and an incredible amount of time

– “a year to make just one watch” [1] (Fig. 1).

Perfecting automatic watches has been in flux for several centuries because it has been a constant

challenge for engineers and watchmakers to overcome restrictions and limitations in both space and

parts. Alterations in today’s constructions of these watches have come close to perfection, making

the fundamental mechanics virtually the same across all automatic watches.

Distinction between Automatic and Digital

In modern-day society, the two most popular watches that are still sold around the world are the

automatic and the digital. Most of us are more familiar with the digital version of the watch because

the digital version is cheaper. A digital watch is composed of an integrated circuit, quartz crystals for

timing purposes, and its life force, the battery; while automatics are entirely made up of mechanical

parts such as screws, rotors, mainsprings, ratchets, and gear trains, all without the need to drain its

life force from a source (Fig. 2).

Figure 1: A labeled diagram of the interior in an automatic watch. The asterisks correspond to parts that are underneath this layer: mainspring (top asterisk), wheel train (left asterisk), and balance assembly (right asterisk). Source: [2]

A huge distinction between both watches is that the second hand “ticks” for digital watches, and in

contrast, “sweeps” smoothly for automatic watches. There are other minor differences in terms of its

shape and size, but this is how most people differentiate the two watches.

No Batteries? – Physics Unveiled

The Black-Box Model

It sounds counter-intuitive to think that a watch could be powered without any batteries at all. In fact,

automatic watches are powered by a rotor that spins from the movements of the wearer’s arm, as

shown in Fig. 3.

Figure 2: Comparison between the inside of a digital (left diagram) and an automatic watch (right diagram). In the left diagram, the battery is placed in the circular hole. Source: http://forums.watchuseek.com/f9/pic-request-tag-heuer-analog-digital-watches-147754.html, [3]

Figure 3: Diagram of a rotor. The rotor can be seen from the back of an automatic watch. It is the shape of a semi-circular plate of metal. Source: http://www.watchalyzer.com/victorinox-swiss-army-watches/victorinox-professional/victorinox-swiss-army-alpnach-automatic-chrono-watch/

But, to fully answer the question of how the movements are able to translate into energy, we must

first consider the “black-box model”. Across all engineering and science, a system can always be

analyzed in terms of its inputs and outputs. Inputs and outputs can be anything from physical aspects

such as a function generator to physical matter such as mechanical and electrical energy. The black-

box represents the system and anything inside of it is irrelevant to the analysis. From physics, the law

of conservation of energy must be satisfied; therefore, the inputs and the outputs from a black-box

must be quantitatively equal [4]. To illustrate, if boiling water touches an ice cube, the result is

lukewarm water because the heat lost from the boiling water is equally gained by the ice cube. Thus,

the law of conservation of energy is conserved.

If we consider the automatic watch as a black-box, we could understand where the physical work has

gone simply by evaluating the inputs and the outputs. In the black-box of an automatic watch, it will

enclose the whole watch which includes rotors, gear trains, mainsprings, ratchets, etc. The black-box

model includes three input sources: mechanical torque of the crown, inertial forces from physical

acceleration, and gravitational forces from Earth [5]. Correspondingly, the outputs from the black-

box model are the constant mechanical torque from the mainspring gear, and the heat from friction

after the mainspring is fully wound [5].

Dynamics of Rotor Motion

Analyzing this problem next requires an analysis of the dynamics of the rotating rotor with the

mainspring gear. In 1780, Louis Recordon, a watchmaker who contributed in developing the

automatic watches, describes the position of the rotor in his patent: “The piece is so fixed… that it is

the centre of gravity to the weight being so poised…[that] the whole turns freely on a screw” [6].

From an engineering perspective, this means that the rotor is an unbalanced pivoted mass that is free

to rotate 360 degrees about its pivot. Furthermore, the weight is “poised”, or fixed, in distributing

where the center of mass (“centre of gravity”) is located. Thus, it is distributed in a specific way to

maximize the inertia of the rotor about its pivot. The moment of inertia is crucial to the design of an

automatic watch because by definition, it is the tendency for a mass to stay in motion while moving

allowing it to build up kinetic energy, energy of being in motion. Because the distance is also

proportional to the moment of inertia, it would be logical for most of the mass to be placed further

from the pivot, therefore, greater inertia.

When a person suddenly jerks his hand forward, there is a sudden instantaneous acceleration in the

reverse direction, similar to the feeling of the force acting backwards on you when you accelerate a

car. Because of the restriction from the pivot, the rotor cannot move linearly in the direction of its

acceleration, but to move circularly in the watch. The rotational motion from the pivot creates

angular momentum and rotational energy, both properties that are proportional to its moment of

inertia [4]. From conservation of energy, the rotational energy coming into the watch is then

gradually converted into potential energy (“stored energy”) of the mainspring in the watch to use as

mechanical torque [4]. To better understand how potential energy physically works in a spring, it

could be thought of as a coiled wire becoming tighter through twisting. Similarly, the conversion to

mechanical torque could be thought of as the opposite process— the tendency of the mainspring to

unwind itself from the increasing built-up tension. This process will continue until the mainspring

grows enough tension to counteract the rotational energy by decelerating the circular movement until

the rotor comes to a complete stop [4].

When the potential energy of the mainspring has passed the energy threshold, extra energy coming

into the mainspring becomes a power reserve for the watch to use as backup [5]. However, this is a

problem because potential energy could not realistically rise to infinity; therefore, exceeding the

maximum energy that could be attained by the mainspring is a crucial problem because it could

damage the watch. Fortunately, Patek Phillipe invented the “overwind protection mechanism” using

a slipping bridle mechanism, which is a mechanism where “the outer coil of the mainspring is not

physically attached to the barrel wall, but rather maintained there by the pressure of a bridle that’s

free to slip – allowed the modern automatic watch as we know it to be developed” [3] (Fig. 4).

For simplification, think of this process as breathing, where the air coming in represents the potential

energy increasing, and the moment you cannot breathe in anymore air represents the maximum

energy at which the mainspring can hold. The “slipping bridle” would be the mechanism that forces

you to exhale, in order to balance out energy coming in.

Summary of Analysis

Returning to automatic watch as a black-box, the dominant factor in the input is the inertial forces

from physical acceleration [5]. Other inputs such as the gravitational force contribute a small amount

in comparison to the quantitative value from the inertial forces. On the output side, the mechanical

torque provides the winding of the watch [5]. Small amounts of heat from friction are also produced,

Figure 4: Slipping bridle and the overwind protection mechanism. The slipping bridle is shown in (1). (2) shows where it is placed. (3) indicates the outward pressure on the mainspring coil. The slipping bridle locks on to a notch when the mainspring is less than full wind (4). At full wind, the lock is let loose and releases tension (5). Source: [2]

but because its value is slight, the output rate is largely constant from the mechanical torque from the

escapement [4]. Intuitively, this is also logical because a watch must have a constant tick for each

second. With this in mind, it becomes clear how the automatic watch works: there must be minimum

required energy from inertial and gravitational forces to offset the constant output rate of the

mainspring and the heat dissipated [7]. In order to maintain a reliable time-keeping watch, the

average value of the inputs must be greater than the average value of the outputs [7].

What has changed to the Automatic Watch?

While the physics of automatic watches have not changed, the design of automatic watches has

changed significantly over the years. The start of the automatic mechanism began in the 1770’s by

Abraham-Louis Perrelot, a Swiss watchmaker who “made the first practical self-winding watch” i.e.

the invention of the rotating rotor mentioned previously [6]. His revolutionary design caused many

watchmakers such as Abraham-Louis Breguet, Adrien Philippe, Antoni Patek, and Jaquet-Droz,

some of whom went on becoming big name watch companies, to improve on his design of self-

winding watches [6]. When John Harwood turned self-winding watches into self-winding

wristwatches ("the modern automatic watch"), it quickly became known as one of the most

innovative design and "one of the finest achievements of Swiss mechanical manufacture" [3][7].

“The degree of precision which has been achieved in small movements” is undoubtedly a success in

manufacturing methods in engineering [7]. A while later, Rolex furthered the concept of the

wristwatch by introducing the first waterproof case and screwdown crown [3]. Modern designs of

high-end automatic watches now include jewels such as diamonds, platinum, gold etc. integrated

with its complex inner workings and are being constructed with careful craftsmanship and precision

making them more durable and long-lasting [8] (Fig. 5).

Effects on Contemporary Society

It is quite an invention to see that the idea of the automatic

watches was conceived in the 18th century. When digital

electronic watches came into existence in the 1970s, they

dominated the industry for its mass production and its superb

accurate timing from quartz oscillation of the crystals [9]. This caused a sudden drop in the

development of automatic watches, which made them even more valuable as collector items. With

automatic watches becoming rarer, they have continued to be a luxury item, a representation of its

class and sophistication. Most automatic watches are generally hand-made with each piece taken

with delicate care. Because their complicated movements and construction are labor-intensive, they

were expensive, as it would be expected for any reliable mechanical watch that has been elegantly

crafted.

Like any paintings, wines, or sculptures, automatic watches are a form of art. But, today art is only

half of what watchmaking is. Engineering has contributed a prominent role in its development

making it “become very largely a science, or rather a production of the chemical, physical and

mechanical sciences” [7]. It is the product of art and science that “[t]he standard modern watch,

whether large or small, has all the appearance of being a perfectly organized mechanism…and that it

has attained its definitive form” [7].

Figure 5: Example of a modern design by Patek Philippe – Calatrava. “It is the result of an avant-garde philosophy of aesthetics that showcases sleek lines and subtle elegance; the collection expresses artistic ingenuity at its very finest. The endearing quality of the design reflects the relentless pursuit of perfection that has always been at the core of Patek Philippe's mission”. Source: [10]

Conclusion

No matter how big or small, each piece in an automatic watch is vital. When assembled perfectly, the

movements become smooth in conjunction with other parts, as if each piece has its own heartbeat.

The beauty of engineering has allowed the development of automatic watches to extend to no end.

That is, it has exceeded mediocre quality, average quality, and high class qualities. To that end, the

modern engineering of an automatic watch is not high quality. It is sublime quality. A mechanical

watch may seem old-fashioned to the common customer, but its combination of the materials,

aesthetics, and movement requires precision and incredible attention to detail, ultimately to provide a

watch to a “clientele who are not greatly concerned with knowing the time” [7].

References

[1] A. Adams. (2010, October 13). Why are watches so expensive? [Online]. Available:

http://www.ablogtowatch.com/why-are-watches-so-expensive/

[2] W. Odets. (2007, December). Illustrated glossary of watch parts [Online]. Available:

http://people.timezone.com/mdisher/WatchSchool/pdfs/TZIllustratedGlossary.pdf

[3] J. Forster. Wind me up, wind me down: a history of the self-winding watch [Online]. Available:

http://people.timezone.com/msandler/Revolution/comp_history15.pdf

[4] W. Arnstein. Physics of the automatic watch’s winding system [Online]. Available:

http://home.att.ne.jp/gold/GT1300Junior/probus/PhysicsAutomaticWatch.html

[5] R. Du and L. Xie, The Mechanics of Mechanical Watches and Clocks, Berlin: Springer, 2013.

[6] R. Watkins, The Origins of Self-Winding Watches 1773-1779, Sydney: Watkins, 2013.

[7] E. Jaquet, A. Chapuis, Technique and History of the Swiss Watch from its Beginnings to the Present

Day, Bern: Urs: Graf-Verlag, 1953.

[8] Anonymous Making time. Architectural Digest pp. 52-n/a. 2010. Available:

http://search.proquest.com/docview/819143646?accountid=14749

[9] A. Young. Markets in time: The rise, fall, and revival of Swiss watchmaking. The Freeman pp. 45-48.

1999. Available: http://search.proquest.com/docview/196600881?accountid=14749

[10] Patek Philippe SA. Patek Philippe SA - Calatrava [Online]. Available:

http://www.patek.com/contents/default/en/calatrava_men.html