Seiko's "Spring Drive" points to the continuous flow of time

"Spring Drive" is a movement system exclusive to Seiko. The smooth sweeping movement of the hands across the dial is one of the many attractions of this movement. In this article, we will explain the sweeping movement of Spring Drive from the perspectives of "continuous" and "discrete."

Rethinking what sweep hand movement is

　Spring Drive is a unique drive system that combines Seiko's accumulated mechanical watch technology with quartz technology. Its distinctive feature is that it reliably drives thick, heavy hands by using the mainspring as power, achieving precision approaching that of quartz watches while smoothly sweeping the second hand. The combination of these two features, which are difficult to achieve in combination with typical quartz and mechanical watches, is a symbol of Seiko's unique technological capabilities. But is that its only advantage?

　When I consider the operating principle of Spring Drive from the perspectives of "continuous" and "discrete," I come to the conclusion that it is a unique mechanism that effectively expresses the continuous flow of time.

　This time, we will explain the concepts of continuity and discreteness in mathematics and control science, and discuss their relationship to time and clocks, while also considering how well Spring Drive expresses the continuous flow of time.

Continuous and Discrete Values

　I believe that it is easier to imagine continuous values ​​if we first talk about discrete values, so I will now talk about discrete values.

　A discrete value is a number that is discontinuous and has no values ​​in between, like integers such as 1, 2, and 3. A typical example of a discrete value is a quartz clock with a digital display. For example, if it is 3:10 minutes and 3 seconds, the time is displayed clearly in numbers as "03:10:03," and after 3 seconds it is displayed as 4 seconds, and no intermediate times are handled. Eventually it moves up to 11 minutes, 12 minutes, etc. This is the idea of ​​handling values ​​discretely.

　A quartz watch measures exactly one second by having an IC divide the high frequency vibrations (approximately 32,768 times per second) produced by the oscillation of a quartz crystal oscillator. Although it operates at very short time intervals, the characteristic of discrete time is that it cannot handle time at finer intervals. This is similar to an apple made of toy blocks, which can only be divided by the gaps between the blocks.

　A continuous value is not an accumulation of such smallest units, but refers to a state in which it can be cut into pieces without limit. In the previous example, a real apple can be cut into pieces no matter where you put the knife.

　Time is a continuous value, and can be divided infinitely into half a second, and so on. The sundial, the original clock, can divide the position of the sun that casts the shadow used to display the time, and the angle of that shadow, infinitely into small divisions. From this point of view, we can see that the sundial treats time, which is a continuous value, as a continuous value.

Considering the operation of a mechanical watch from the perspective of continuous and discrete time

　Many mechanical watches that display time with hands are often said to have a beautiful feature in that their second hands move precisely. From this point of view, the time shown by a mechanical watch seems to be a continuous value, but if we think about it strictly from the perspective of continuous and discrete time, we can see it differently.

　Many mechanical watches have a mechanism that transmits the reciprocating motion of the pendulum or balance wheel to an anchor, limiting the amount of unwinding of the wound mainspring within a certain period of time. Because the mechanism moves the smallest unit of time when it reaches the end of its reciprocating motion, time is measured in units of half a cycle of reciprocation. For example, the Seiko Cal. 9SA5, a high-beat movement that operates at 36000 vibrations per hour, moves the anchor once every 0.1 seconds, advancing the second hand by 0.1 seconds.

　In other words, this movement accumulates 0.1 seconds, the smallest unit of time it handles, to indicate 1 second and 1 minute, and the time displayed on the dial can be thought of as changing discretely.

Spring Drive operating principle

　The power source that moves the hands of a Spring Drive watch is the mainspring; it does not have a balance wheel or anchor, and the speed of the rotational motion caused by the mainspring unwinding is controlled by an electromagnetic brake.

　If the rotation speed can be limited so that the second hand moves only 6 degrees per second, it will rotate 360 ​​degrees per minute and function as an accurate clock. I say "per second" here, but that one second within the movement must be accurate.

　For example, suppose the second hand moves 30° over a certain time interval. If this lasts exactly 5 seconds, the clock will be accurate, with the second hand moving 6° per second. However, if this movement is 30° over 6 seconds, it will move 5° per second, which means it will only move 300° per minute, and on the clock face it will be 10 seconds slower per minute. Therefore, in order to accurately move the second hand at a rotation speed of 6° per second, it must be controlled at more precise, known time intervals.

　This precise time interval is controlled by a control circuit that uses the oscillation period of a quartz crystal. By using a quartz crystal to oscillate, it is possible to obtain a voltage fluctuation with a constant period, and by using this as a trigger, a precise time interval can be obtained.

　Electricity is required to operate this control circuit. Spring Drive operates on electricity generated by an electromagnetic brake. Let's think about a bicycle dynamo light. When the bicycle moves forward, the dynamo light's generator rotates, obtaining electrical energy and causing the light to light up. At the same time, energy is taken from the generator, which is subjected to a force opposite to the direction of rotation, causing it to slow down. This is the principle by which an electromagnetic brake also functions as a generator.

Spring Drive expresses the continuity of time

　The unwinding force of a tightly wound mainspring is continuous, without interruption. This causes the rotating gear train to move continuously. Spring Drive controls this rotation by slowing it down. This control is performed at short intervals, but it does not stop the rotation, so the movement of the gear train is maintained continuously.

　This is a major difference from quartz watches, which count time at fixed intervals, and mechanical watches, which calculate the smallest unit of time based on the vibration period. Unlike many other movement systems, Spring Drive expresses continuous time as a continuous hand position, which can be said to be a major feature.

Finally

　The discussion so far has been a classification of the operating principles of various watches from the perspective of continuous and discrete, which are concepts of mathematics and control, rather than a consideration of their relative merits. Just as we find the appeal of watches in the finishes of the movement, case, and dial, the difference in the movement of the hands due to different vibration frequencies, and the feel of operating the crown, we are proposing that we reflect on the process of expressing intangible time on the dial.

　Watching the smooth sweep of the second hand and feeling the uninterrupted flow of time is a privilege given to users of Spring Drive models. If you are interested in or have purchased a model that is by no means inexpensive, I would like to suggest that you would get the most out of it by enjoying it from various perspectives.

　If you are interested, we hope you will pick it up in store and enjoy it while remembering the contents of this article.