An experimental conveyor belt cart was designed to carry 12 envelopes. Each pocket is accompanied by a binary escort memory.
Each wheel can be in one of two positions on the shaft that carries the wheels. One position of a wheel indicates a binary "zero", and the other position indicates a "one". With 13 wheels the system will sort an envelope into one of more than 8,000 receptacles. In practice, the machines used by the post office sort into about 400 separations, so 10 wheels are used for direct sorting; the other 3 wheels can change the sorting at different times of day and used for other purposes.
The operation of the escort memory involves wheels rolling on a surface consisting of flat "tracks". These tracks can be pre-set so the wheels roll over them when they do not match the arrangement of the tracks. But when a particular array of wheels drop, its impact releases a trap door under the envelope. The envelope falls into its correct receptacle. The action of the wheels can be compared to the action of the four wheels of an automobile when they simultaneously fall into 4 deep ruts in the road.
This particular escort wheel memory was invented by Lawrence Kamm, Chief mechanical engineer of Rabinow Engineering Company.
During the following thirty years, about 600 of these letter sorting machines were built for and used by the Post Office. Later "shishkebab" memories (nickname) were replaced by computer memories while the basic conveyer remained intact.
Each machine and its coding stations required 12 operators. In some later operations the manual control of sorting was by-passed when optical address readers were developed and mark sensing of envelopes was adopted for some of the sorting operations.
With this new machine, each operator sorted 60 letters per minute into 400 receptacles. This resulted in 18 times greater efficiency than hand sorting.
Last Updated on October 24, 2004
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