Citizen Watch Co Ltd will release what it claims is the world's most accurate quartz wristwatch in the fall of 2019.
It is a solar-powered wristwatch priced at ¥1.8 million (excluding tax). Its product name is "The Citizen."
"We employed a wristwatch technology that enables to most accurately mark the passage of time in the world," Citizen said in a statement.
By using parts that were formed with a high accuracy, Citizen developed the "Caliber 0100" watch movement, whose margin of error is only ±1 second per year. The annual margin of error of the company's existing solar-powered quartz wristwatches is ±5 seconds.
For the wristwatch, Citizen formed gears and springs by using UV-LIGA (Lithographie Galvanoformung und Abformung) process, a MEMS (micro-electro-mechanical system) technology. The company made molds of ultraviolet (UV) curing resin by photolithography using UV light. With the molds, minute parts having three-dimensional structures are made by electrocasting.
With this method, the "third gear," "fourth gear," "fifth gear" and "third return gear" were formed. The third return gear has a structure combining a gear and spring, and the spring is formed by using the UV-LIGA process. The process enables to make parts having small eccentrics with a high accuracy, compared with conventional parts made by cutting and pressing.
The third return gear is a part for reducing backlash (looseness between tooth planes when gears mesh with each other). The third return gear is pressed in the direction opposite to the moving direction of the gear by using the force of the spring so that the gap (backlash) is moved to one side. It prevents the hands of the wristwatch from shaking.
For the new quartz wristwatch, Citizen used a different oscillator. Specifically, it employed an "AT cut-type" quartz oscillator in place of a "tuning fork-type" quartz oscillator. The frequency of the AT cut-type quartz oscillator is 8.4MHz, which is 256 times higher than that of the tuning fork-type quartz oscillator (33kHz). The higher the frequency of quartz oscillator, the easier it becomes to improve accuracy.
Also, the AT cut-type quartz oscillator has excellent temperature properties and a high stability at a temperature of -5 to 40°C (it is not distorted much). Furthermore, it is not much affected by gravity, whose influence changes depending on the position of the arm, or aged deterioration.
The problem of power consumption was solved by combining low-power consumption technologies that Citizen has built up so far. With those measures, the new quartz wristwatch realizes a high accuracy, and its margin of error is less than one second (0.9855 seconds) even after one year of use.
Citizen will offer a limited number of the product (100 units), emphasizing its rarity. Its case is made of 18-karat gold (ratio of gold: 75%), and its band is made of alligator leather. The diameter and thickness of the case are 37.5 and 9.1mm, respectively.© Nikkei x Tech