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The photographers stamp on this photograph reads: HALL & CO. Commercial Photographers 20 Hunter Street Sydney
The storage screws, a mechanical form of memory can be easily seen. There are nine large rotating shafts running from the ends of the adding shafts to cogs at the front of the adder, on the lower assembly and another two on the upper assembly running from the adding shafts on the left, to cogs on the right side of the adder. These are the storage screws. The purpose of the storage screws is to buffer the rotation of the rapidly accelerating adding shafts from machinery that is slower to respond due to greater inertia. Simplistically, the fast adding shafts screw a grub-screw like screw into the threaded inside of the storage screw shaft called a nut. The slower to accelerate equipment at the other end of the shaft unwinds the screw as it accelerates, acting to return it to its starting position, by winding the threaded outer shaft of the storage screw. Eventually the slower to accelerate equipment will reach a greater velocity than the adding shafts and start to catch up. There are rods that are visible in the image projecting from this slower to accelerate, right hand end of the storage screws on the upper assembly. These are part of a mechanism that detects when the storage screw is returning close to its resting position causing the catching up velocity to reduce and eventually cease when the screw has returned to its rest position. Conversely, it controls the amount of acceleration during the start of rotation dependent on the rate that the storage screw is advancing. This protruding rod from the end of the storage screw seems to be associated with a lever and what look like nearby drive pulleys so I suspect this is a method of angular velocity control. It appears that the velocity of the nut part of the storage screw is controlled by varying the tension of the drive belt with a pulley in the drive train that can alter the tension of the drive belt. There seems to be more than one method of implementing the variable friction to control the angular velocity. Another is through a clutch arrangement. George Julius wrote about this in a paper he presented to the Institution of Engineers Australia in 1920. His reference to the counters does not relate to this adder and can be taken to mean slow to accelerate equipment in this case. An extract reads:
The movement of this screw is so arranged that it also controls a variable speed friction gear through which the counters are driven. During any period of acceleration in the issue of tickets, the screw is withdrawn in the nut faster than the counter operates, and this through the friction gear speeds up the counter, and the nut, in an endeavour to overtake the movement of the screw, and a condition of balance is ultimately established. If the issue of tickets is retarded or ceases, the nut immediately gains on the screw and brings it forward, thereby picking up all the stored-up records, and by means of the friction gear gradually slowing down the counter until when all the records are recorded, it quietly comes to rest. The rotation of the nut also is utilised to continually rewind the coil spring which operates the epicyclic gears, and thus ensure a steady driving effort on these gears. There is a drawing of the storage screw in the second page of the Photo Gallery in the same section as previously mentioned.
George Julius presented a paper to the Institution of Engineers Australia on Thursday May 13th 1920 describing these systems, when a machine that had been built and tested capable of supporting 1,000 terminals and a sell rate of 250,000 bets per minute was demonstrated.The part of George's paper that is pertinent to this website is presented in the Mechanical Aids to Calculation chapter of this website.