Mechanism of "Man-nen dokei", a Historic Perpetual Chronometer (2nd Report, Power Supply)

Abstract

The “Man-nen dokei”, which is a historic perpetual chronometer, was made in 1851 by Hisashige Tanaka, who founded the predecessor of Toshiba Corporation. It has six multi-functional clock faces and a celestial globe. It is said that it runs for almost a year with just a single winding. Man-nen dokei was disassembled and restored in a national project. We investigated on the mechanism of Man-nen dokei in cooperation with this project. In this paper, we report on the mechanism of the power supply. As a result, from mechanism constitution of the power supply, we confirmed that maximum continual movable days of Man-nen dokei were approximately 225 days. But from the fusee steps and the double spring composition, it is thought that Hisashige's goal was to make it move for 1 year continually. The spring that generates the huge torque became necessary to make it move for 1 year, but it is assumed that the spring were wound just a little due to strength poverty of the wooden frame. Moreover, we think the composition of one fusee is a reasonable design to obtain necessary torque continuous operation with stability for 1 year, and the reason why Hisashige used composition of two fusees still remains to be unclear.