Magic Lever Technology

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Wearables Mechanical technology

Developing the Magic Lever Technology that Underpins Self-winding Wrist Watch

Most high-grade watches have a mechanical movement, which uses a mainspring to power the watch. Over 60 years ago, Seiko Epson (then Suwa Seikosha but referred to below as Epson), assembled the intellects of its engineers to develop a so-called magic lever. This became the fundamental mechanism underpinning typical self-winding wrist watches up to the present day. Thereafter, it also triggered a proliferation of self-winding wrist watches in Japan. Let's take a look at the original self-winding "magic lever" technology that Epson developed.

The inner workings of mechanical watches

The mechanism by which a watch operates, known as an engine or movement, can be broadly classified into two types: quartz and mechanical. The quartz type uses a battery, so is also referred to as a battery type. In contrast, mechanical movements do not use a battery. Energy is stored by winding a mainspring, which consists of a metal strip or hair-thin metal strip (wire) in a spiral. The force generated when this energy is released operates the watch.

Mechanical watches are classified as either hand-wound or self-winding. As the name suggests, the mainspring in a hand-wound watch is wound by turning the crown on the side of the dial. Likewise, the mainspring is automatically wound in a self-winding watch. Simply wearing the watch on your wrist or placing it on a specialized device that mechanically generates oscillations is needed to wind the mainspring.

The mechanical movement is equipped with a semicircular oscillating weight about half the size of the dial. The motion of the wearer's arm causes this oscillating weight to rotate naturally and automatically generate energy. For this reason, self-winding wrist watches are also called "automatic".

The inner workings of mechanical watches

The history of self-winding technology

The origins of self-winding watches date back to the late 18th century. They begin when a Swiss watchmaker developed the first self-winding pocket watch. However, the mechanism employed at the time was not practical, so it did not come into general use. Nevertheless, the idea began to garner attention again in the late 19th century. In 1910, a self-winding wristwatch appeared. Entering the 1920s, a French chronometer manufacturer (chronometer refers to a standard for ensuring high quality and precision, as well as the products made to this standard) succeeded in creating the world's first self-winding wristwatch. Soon after, an English watch engineer succeeded in mass producing self-winding wrist watches.

Then in 1931, a Swiss watchmaker announced a water-resistant self-winding wristwatch, and began mass production and sales. Thereafter, watchmakers around the world used this model as reference to develop and sell their own self-winding wrist watches. Self-winding wrist watches soon spread widely among the general public.

The development of self-winding wrist watches in Japan trailed watchmakers overseas by more than a decade. It began with the announcement of the Seiko Automatic, Japan's first self-winding wristwatch, by Daini Seikosha (now Seiko Instruments) in 1956.

After this, other Japanese watch manufacturers followed Daini Seikosha in announcing self-winding wrist watches. But these were all two to three times the cost of the hand-wound watches of the day. Epson recognized that cost was an important factor in popularizing self-winding wrist watches, and pressed forward with development of a new self-winding wristwatch that could be mass produced.

Developing the original magic lever self-winding technology

When development began, the plan was to base it on the mechanism from an existing foreign-made self-winding wristwatch. However, when development had progressed to the point of a completed prototype, it was discovered that a patent had already been submitted for the technology. Therefore, the same mechanism could not be used. The company had to invent its own original self-winding mechanism from scratch. Engineers tossed around various ideas, continuing to contemplate and search for the best self-winding wristwatch mechanism, from the perspective of dynamics. The result was the invention of an original, cutting-edge, and breakthrough self-winding mechanism: the magic lever.

As noted earlier, the basic principle of self-winding wrist watches is to transmit the energy generated by the oscillating weight to the mainspring. To explain in more detail, while the oscillating weight rotates in two directions, the mainspring winder only turns in one. Therefore, the question becomes how to efficiently transmit energy between these two mechanisms of differing rotations without waste. In response to these challenges, our engineers came up with an entirely new and unique winding mechanism. This mechanism relies on a small component with pawl-shaped tips called the pawl lever. (This was publicly christened the magic lever due to its motion, which was inspired by dynamics and allowed a single part to perform multiple functions.) We'll explain a few of the particularly key technologies.

Key technology 1

Offsetting the central axis of the lever

The magic lever's axis of motion is purposefully offset slightly from the central axis of the oscillating weight. This is done because such a design ensures that the magic lever will move up and down regardless of whether the oscillating weight rotates to the right or left. This idea makes it possible for the energy generated by the oscillating weight to be efficiently transmitted without waste.

Key technology 2

Different pawl shapes for the left and right

If you look carefully at the illustration, you can see that the pawl-shaped tips of the magic lever differ between right and left. This difference in shape ensures the up and down motion of the magic lever is converted to rotation in the same direction, whether the lever rises or falls. This makes it possible to turn the transmission wheel and wind the mainspring.
When the magic lever rises the push pullet pushes the transmission wheel, turning it to the left. At this time, the pull pullet slips past the transmission wheel without moving significantly away from it. When the magic lever descends, the pull pullet pulls on the transmission wheel, turning it to the left. At this time, the push pullet slips past the transmission wheel without moving significantly away from it.
Because the motion and winding method appear almost as if magic, the mechanism came to be called the magic lever. Moreover, since the magic lever itself is made of spring material, it does not come away from the gear that winds the mainspring (transmission wheel), even when the pawls do not mesh with the gear teeth, or the oscillating weight is not moving.

The brilliance of our engineers distilled into the Gyro Marvel

The Gyro Marvel, which first equipped the magic lever mechanism

The idea and design were set. But the company had no experience in bringing something like this to market. There were still various hurdles to overcome. These included improving the overall technology and precision, reconsidering materials, and finding new suppliers for these materials. The engineers of the time cleared each hurdle, one-by-one, through introducing new machinery and equipment, adding heat treatment to prevent deformation, and implementing other solutions.

To ensure both highly efficient rotation and vibration resistance, both the oscillating weight and the ball bearings used in the shaft were re-examined starting from their raw materials. They even developed an ultrasmall ball bearing. Various types of oil were newly developed as improvements on the oils used in the tenon of the eccentric post, or to optimize the slip torque of the mainspring. The key part in the system, the pawl lever, depended on the success of the volume production technology. So the company gathered a great number of engineers who worked with pressing to share knowledge and exchange ideas. They hammered out details such as the optimal thickness, width, and tip shape, through trial and error.

Thanks to the hard work of these engineers, in 1959 the Gyro Marvel, Epson's first self-winding wristwatch equipped with the magic lever, was revealed to the world. This mechanism so dramatically increased mainspring winding efficiency, that it spread to become a typical mechanism used in self-winding wrist watches thereafter. And it continues to be used in self-winding wrist watches to this day. The price was also held down to just slightly higher than hand-wound watches, contributing to its widespread adoption. This also triggered the popularization of self-winding wrist watches that followed.

As we have explained, the Epson engineers of the time overcame many obstacles to make the new self-winding mechanism, with its magic lever, a reality. And when they surpassed these challenges, they found they had a new technology at their disposal. However, technology is not all that they gained. That is to say, watch manufacturing up to that point had generally emulated the style of the Swiss manufacturers. But following the development of the magic lever, there was growing momentum to pursue the development methodology that had brought forth the development of the magic lever technology. And this kind of momentum gathered steam over many years, fomenting the creation of things that had never existed before. This spirit of pursuing Creativity and Challenge has been passed down as a part of Epson's DNA to this day.