Events and Sightings

Restoration of the Differential Analyzer at the Tokyo University of Science

At one time, there were at least three mechanical differential analyzers in Japan, installed at the University of Tokyo (4 integrator units, 1942?), University of Osaka (3 integrator units, 1944?), and University of Tokyo (8 integrator units, 1954). Later, the Osaka machine was sent to the Tokyo University of Science and kept in its Museum of Science for exhibition. It was certified as an Information Processing Technology Heritage in 2009. The two other analyzers were abandoned.

Hearing that the Manchester Museum of Science and Technology restored its differential analyzer, we were tempted to resurrect our survivor as well. After determining that a “heritage” computer could actually be modified, in April 2013, a new project was kicked off to restore the differential analyzer to working condition. The project core was made up of the Tokyo University of Science, National Institute of Informatics (NII), and National Institute of Information and Communications Technology (NICT).

The first step was to examine the current state of the machine. Since the machine was assembled after being moved from Osaka by nonengineering people, there were many components incorrectly connected. To keep parts from rusting, shafts, gears, and adders had been painted with layers of lacquer. In addition, the driving belts of the torque amplifiers were broken, and disc surfaces were scratched. It was quite a miserable sight. On 15 June, a team of students from the Mechanical Engineering Department was summoned to the museum to measure every dimension of the machine and to draw precise plans. After that, two of the three sets of integrator units and torque amplifiers were removed from the bay frames and taken to the NICT machine shop for repair.

On 20 September, the remaining shafts and gears were removed from the bay frames, dipped in a vat filled with thinner, and kept there for two or three days and nights. The student team was then asked to remove the lacquer by patiently washing each part. The cleaned shafts and gears were returned to the original positions in the bay frames. Then they were turned freely. In August, at the NICT machine shop, the first integrator unit was thoroughly studied and all parts were removed, cleaned, and checked to see if they were worn out. Some parts were missing. In those cases, the worn or lost parts had to be made anew.

For the large integrator disc to be reformed, its axis was clamped on a turning lathe, and the surface was scraped carefully until a flat plain appeared. Parts of the torque amplifier were also completely removed. The drum surfaces of the primary and secondary stages were ground, and in so doing, a few prototypes of string holder mechanisms were designed and tested. Because the designers foresaw that the strings would need to be adjusted often, and the space in the torque amplifier was so small, the string holder could be handled easily. However, the material of the friction strings posed a problem. In an interview, Professor Emeritus Masaru Watanabe, who had actual experience with both of the differential analyzers at the University of Tokyo, recalled that they used koto string for it long ago. (Koto is a Japanese classical musical string instrument.) Koto string is still available, so it was chosen for the first stage. For the secondary stage drum, kevlar cord, a kind of poly chemical substance, was the sole solution. The first torque amplifier and integrator set was combined in December, although the output torque proved far weaker than expected.

In January and February 2014, the amplification ratio was measured by repeatedly changing the tension, friction, and number of turns. Wrapped with sample string, the drum was rotated slowly on a lathe, and both ends of the string were pulled by a pair of spring scales to calculate the ratio. Finally, an amplification on the order of a thousand was achieved.

By the beginning of April 2014, the first set was complete, so the restoration for the second set of integrator and amplifier began. This process moved rapidly, and the second set was completed...