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Engineers Pursuing the Ultimate in the Evolution of Wristwatch Technology:
Seiko Instruments Inc.
Seiko Instruments Inc.
Throughout modern history, wristwatches have always represented the fusion of the best technologies available. Various technologies--such as precision engineering, metallurgical engineering, measurement, control, electronics, electrical engineering, energy engineering and information technology--have been involved in the development of wristwatches. Here, we can also find the engineers' dreams to pursue the further evolution of wristwatches.
Seiko Instruments Inc. (SII) is a company that has proposed a new sense of value in various fields. These fields are divided into four categories, called WINS, described as follows:
Wearable: A field dealing with various electronic devices represented by wristwatches.
Industrial Systems: A field in support of the development, manufacture and inspection of products such as semiconductors.
Network Components: A field to develop electronic parts used in network devices and terminals such as cell phones.
E-Solutions: A field dedicated to improving terminals, network services, and other technologies needed for e-business.
The basis of the evolution of WINS is the solid technology and culture established through the manufacture, research and development of wristwatches.
In this article, we introduce two forefront technologies that we have developed from wristwatch technology.
SEIKO Perpetual Calendar with Ultrasonic Micromotor
Fully Automated Calendar Function till the Year 2100 Is on Board
Modern wristwatches are densely packed with a variety of micromechanisms, including power sources, generators, oscillators, control circuits, gears, micromotors, microtransmission devices, microsensors, liquid crystal plates, and so on. The SEIKO Perpetual Calendar has some great strong points: an auto-turn calendar, set to function without any revision till the year 2100, is now on board. It is accurate to within 20 seconds per year, and the battery life for the men's version is 10 years (5 years for the women's version). These merits show us that the SEIKO Perpetual Calendar aims at becoming the new standard among wristwatches in the 21st century. An ultrasonic micromotor, researched and developed by SII, is installed in the watch as the driving source for calendar mechanism. It is not too much to say that this application of ultrasonic motors on a wristwatch is pioneering.
An ultrasonic motor is a motor that is driven by the elastic ultrasonic vibration of piezoelectric elements, which resonates at more than 20kHz (20,000 vibrations per second). This technology was developed in Japan in 1981. The ultrasonic motor is superior to the magnetic motor with magnetic circuits for the driving function: no influence from magnetic fields, small size, high torque, fast response, ability to execute extremely small movements, high static torque, and so on. It is well known that an ultrasonic motor is used for the driving source of auto-focus cameras, and the motor is also used as the driving source of rolled curtains and medical MRI (magnetic resonance imaging) which deals with strong magnetism, and other devices.
Ultrasonic motors have a great potential to serve as the driving source of micromechanisms, as represented by watches. However, there is a big problem not only with the need to miniaturize the motor, but to miniaturize the circuit for driving the motor. There are two types of ultrasonic motors: "traveling wave type" (in which the wave proceeds in one direction), and "standing wave type" (in which the wave moves in one place). It is easy to change the direction of rotation in the traveling wave type, but double-phase driving (to drive the motor with a combination of two signals) and high voltage are necessary, and the circuits are very complicated. With the standing wave type, on the other hand, single-phase driving is possible, but the direction of rotation has been just one way until now. Beside this, a great number of other problems remain to be settled before ultrasonic motors can be made to work in small and precise wristwatches. These problems include the slight fluctuation in resonance frequency for drive owing to fluctuations in voltage, temperature, dispersion of processing, etc., which requires complicated control circuits to revise such fluctuations.
The World Smallest Ultrasonic Motor in Practical Use --Accomplished by SII's Original Technologies
In the R&D division of SII, the potential of ultrasonic motors has been under study since 1990, and various approaches have been taken to make the technology our own. We have faced and overcome a lot of difficulties one by one. In 1994, we succeeded in changing the rotor direction in the standing wave type (single-phase driving) (Fig. 2) and in making micromotors (Fig. 1) driven by self-oscillating circuits (Fig. 3) with simplified structures. These micromotors were designed for mass production. When we use them in wristwatches, they should be driven with low voltage (1.5V~3V) so that button-size batteries can be used. In order to do that, the piezoelectric elements should be as thin as possible. We succeeded in making the piezoelectric elements thinner--from about 500 micrometer to 80 micrometer--and in driving in less voltage. In 1996, alarm wristwatches driven by an ultrasonic micromotor (8mm in diameter) were put into commercial production. Then, in 1998, the smallest motors in the world (4.5mm in diameter and 2.5mm in thickness) were mass-produced. These ultrasonic micromotors vibrated 630,000 times a second, and when 2.5V was added, such specifications as 15,000rpm without load, 0.2 gf cm of starting torque, and 12mA of no-load current were realized in both rotor directions. These motors have been installed in the Perpetual Calendar with a fully automated calendar turning over till the year 2100. The development of these ultrasonic micromotors garnered two awards: the JSPE Technology Development Award in 1997 and the Japan Society for the Promotion of Machine Industry Prize in 1998. It is not too much to say that SII's challenge for creating new wearable instruments like wristwatches lead these innovative micromotors.
As reported above, practical ultrasonic micromotors have been developed, loaded on wristwatches, and produced on a commercial basis. It is often said that a small and thin structure and high output are difficult to realize in electromagnetic motors. By using ultrasonic micromotors, we can overcome these difficulties. These ultrasonic motors are expected to use applications in medical treatments, wearable instruments and devices for optical communication. Ultrasonic micromotors were originally developed for wristwatches, but their full potential lies in smaller and more highly efficient micromechanisms and wearable instruments.
SEIKO THERMIC, a Quartz Watch Driven by Body Heat
Equipped with the World's Smallest Thermoelectric Device for Practical Use.
In the development of both mechanical and quartz wristwatches as wearable devices, the effective use of external energy, such as light, motion and heat, is traditional technology. One of the first wristwatches to gain external energy is the self-winding mechanical watch. Beyond that, watches powered by solar energy or by kinetic energy drawn from the motion of the arm have been developed and commercialized. However, the thermoelectric conversion by the Seebeck effect (Fig. 4)" has been left behind in the flow of development and commercialization of external energy sources for wristwatches. The main reason for this lag was the difficulty of miniaturizing thermoelectric devices. SII started basic research on thermoelectric conversion in the 1970s, and its full-scale research began in the 1990s. In 1994, SII researchers succeeded in developing a micro-thermoelectric device, which used Bismuth Telluride thermoelectric materials. In 1998, they developed and commercialized SEIKO THERMIC, a heat-powered wristwatch that generates power by utilizing the difference between ambient and body temperatures.
This heat-powered device can be called the ultimate self-powered wristwatch because it operates and generates energy continuously while the user is simply wearing the watch--in other words, the user doesn't have to expose the watch to light or move his or her arm in order to keep the watch supplied with energy.
Success in Development of the World's Smallest Thermoelectric Device for Practical Use
The structure of the heat-powered wristwatch is shown in Fig. 5. In order to provide a temperature difference to the thermoelectric device effectively, the back lid of the watch receives heat from the user's arm as the high-temperature end, while the case emits heat from the back lid efficiently as the low-temperature end. A temperature difference of 1 to 3 C can always be taken between the high-temperature end and the low-temperature end. Since quartz wristwatches consume approximately 1.5 volts and 1 microampere on average, it is necessary for thermoelectric watches to have a thermoelectric conversion device that can generate more than 1.5 microwatts of electricity by the temperature difference of 1 to 3 C. Generally, a single element of thermoelectric devices generates a voltage of 200 microvolts by a temperature difference of 1 C. To obtain 1.5 volts by a temperature difference of 1 C, it is necessary to connect at least 7500 elements in series. It was obvious that extraordinary difficulties would follow in machining the elements and ensuring their reliability.
SII minimized the difficulties of developing such thermoelectric devices by adopting a method of booster circuit by IC and reducing the number of elements in a single device to the lowest possible number. However, it was still necessary to connect about 1,000 elements in a small space. Thermoelectric material is very brittle and is hard to machine. The thickness of a typical thermoelectric element is 1 mm. In order to build a thermoelectric device for a wristwatch, it is necessary to reduce the element's height to 80 micrometers and its size to 600 micrometers. SII developed a micro-thermoelectric device (photograph 3) in which 104 thermoelectric elements are connected in series between two 2 mm x 2 mm substrates. The specification that the 10 thermoelectric conversion devices be connected in series was fixed, and it was built into the wristwatch by strengthening shock resistance and compiling the device into a unit (photograph 4). This is the world's smallest π -shaped thermoelectric device that has thermoelectric elements for practical use.
Major Opportunities for Pioneering Other Fields using a Compilation of Advanced Technology
The system overview of THERMIC, the world's first body-heat-powered watch, is shown in Fig. 6. The system consists of a thermoelectric device, IC for step-up charge and control, a titanium lithium-ion rechargeable battery (voltage 1.5 volts), a driving circuit, and four motors. In this system, not only the micro-thermoelectric device developed for the watch but also many of the latest technologies are installed. The technology related to THERMIC for the micro-thermoelectric device has been admired both at home and abroad. For example, it was awarded the technical development prize from the Japan Institute of Metals in 1999 for its originality and freshness, and the watch is kept on display at the Smithsonian museum in the United States.
For thermoelectric-powered wristwatches to see widespread use, a tough problem to overcome is that its manufacturing cost must be reduced. Both the further miniaturization and high-densitization of thermoelectric conversion devices are important, as they were with other electronic products such as LSI. Moreover, the technology has every possibility of pioneering applicable fields besides wristwatches: for example, applications in electronic devices of semiconductor lasers by using the excellent function as a cooling element.
The wristwatch, which was the first wearable apparatus, has progressed from mechanical to quartz, and at least 900 million watches (only analog type) are produced every year. Japanese makers produce approximately 75% of these watches, which tick on the arms of people all over the world. Although wristwatches are considered to have arrived at their region of completion, they are still developing by the realization of engineers' dreams. The wristwatch-origin technologies will play an active part in the field of wearable computing and micromechanisms in the 21st century, thanks to their compactness, energy conservation, and uniqueness.
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