Modeling the Mechanical Watch using The Department of Defense Architecture Framework (DoDAF)
Domestic watch manufacture in the United States ended in 1969 when the Hamilton Watch Company of Lancaster, Pennsylvania ceased production. This ended an era that spanned at least 100 years. While the company is still in existence, all its watches are now produced outside of the United States. Hamilton's contribution to the precision, quality and beauty of the mechanical watch is represented in the last of its railroad watches, the model 992B, shown in Figure 1. Some have said that the quality seen in the 992B and its contemporaries was so remarkable that today's counterfeiters of antiques cannot economically duplicate it.
Today, many take timekeeping for granted to the extent that some are even abandoning the use of a personal watch to use the time function on their cell phone. For others there is a fascination with the mechanical watch or its heritage that supports a robust market in expensive watch lines such as Rolex, Omega, and even Hamilton. These watches can sell for prices in excess of $6000 even though the cheaper quartz watch is a superior timekeeper.
Since the mechanical watch is not going away in the near future, an abbreviated Systems Engineering model may provide some insight into the physical concepts involved and identify the common principles that the mechanical watch shares with later technology, including the Cesium clocks that are used in the United States Global Positioning (System GPS).
We will use the Department of Defense Architecture Framework (DoDAF) for our model since its guidance is readily available on the Internet. The model's description claims that its views should be selected on a "fit for purpose" basis so only three will be used to model the mechanical watch.
DoDAF views aspire to describe a defined aspect of an underlying model that contains more comprehensive information about the actual system. For this effort we will be content to provide only the data shown in the selected views. Our underlying model if pursued fully would contain a great deal of the information accumulated in over 100 years of engineering improvements. Watch collectors and horologists have available considerable amounts of technical information on mechanical watches ranging from such issues as lubrication of jewels to the development of advanced metal alloys for hairsprings.
The DoDAF, Operational view, OV-2, shown in Figure 3, illustrates the major activities performed by the watch and the resource flows between them. There are only two resource flows: energy and time transfer that together support the activities. The activities in turn provide an independent time reference and display an output by moving clock hands.
The DoDAF, OV-5b, Figure 4, shows the same resource flows as the OV-2 and adds two important external interfaces that service the watch by periodically winding up the watch mainspring and setting the time to an external standard.
Figure 5 shows the DoDAF, Systems View, SV-1 that depicts system modules decomposed into component parts. Note that the wheel (gear) train serves a dual purpose. It both transmits power and communicates information from the Balance Wheel to the Time Display.
After studying the three DoDAF views, we can visualize the individual watch systems' purposes and relationships but have no information on the physical implementation. To understand fully how the watch functions we should view the motions of the balance wheel, escape wheel and the connecting pallet lever. A link is provided here: Watch Animation. Alternately, we can study the exploded views in Figures 6 & 7.
It is important to note that this design is common to the majority of all watches manufactured in at least the last 100 years. Any variations are extensions to the design as opposed to basic changes. An example of an extension would be the self winding watch wherein an internal pendulous weight instead of the watch owner winds the mainspring.
The DoDAF views contain enough information to describe what the watch does and the systems involved. It does not provide information on the mechanical principals of operation or the nature of the communications between systems. In the mechanical watch, gear trains are the means of both transmitting power and communicating the passage of time. A key system feature that is common with all timekeeping devices is the Time Calculator. In practice this is always a form of oscillator that supplies a constant periodic motion or electrical signal. The mechanical oscillator, a balance wheel, has been supplanted with miniature quartz tuning forks (the quartz watch) as well as more advanced concepts that include counting the vibrations of atoms. Quartz watches are at least 5 times more accurate than a mechanical watch but fall short of the accuracy provided by Cesium Clocks. Cesium Clocks cannot be worn on the wrist but anyone carrying a smart phone with GPS installed has access to their output and essentially requires it to provide an accurate geographic location.
Will the mechanical clock as we know it today continue to be developed? The answer is probably yes for at least two reasons. The first reason is that the technology is based on years of design evolution that is well understood and has applications in other industries such as microelectronics. Second, there is always a need in special environments for independent time keeping devices that do not use electrical energy, can be made immune to remote tampering, and may be produced cheaply in large quantities.
Did the DoDAF architecture views aid in gaining an initial appreciation of the major elements and functions of the watch? If not, perhaps there is a latent curiosity to go beyond the Systems Engineering element and delve more into what can prove to be fascinating details. What for instance are the two functions of watch jewels or the purpose of using solid gold wheels in the gear train. If these questions captivate you, the following web sites are worth viewing.
How a mechanical watch works: https://www.youtube.com/watch?v=uGcoIue1Bs8
Hamilton How a watch works: https://www.youtube.com/watch?v=cZwq1KL4SD0
What makes a fine watch fine: https://www.youtube.com/watch?v=qfaT6sfagEE
The Elgin Watch Factory: https://www.youtube.com/watch?v=ys4ChOWYNy8
The final question to present before concluding is: Did the DodAF model efficiently describe enough of the watch design to be a useful exercise? Here we have the elemental challenge of all engineering models - does the effort justify its creation. I believe that in the case of the mechanical watch it does in the sense that it can be an enticing entry into the study of more technical details that would otherwise be avoided or ignored. After all, spending $6000 or more for a watch could justify a little investigation.