In mail collection centers, the piles of letters are sorted individually according to their general destinations. There, they are once again sorted according to their delivery areas - but at that point the automation reaches its limits. Every morning, the mail carrier must take the many hundreds of letters he or she must deliver in the course of the morning and sort them by hand into the sequence of houses along the route. Post offices in the U.S. were the first to start sorting the letters yet again, this time according to each individual mail carrier's route. This process is now standard in many industrialized countries. This is the point at which Zimmermann's invention comes into play. "Very little time is available for this final sorting process, because all of the letters have to be sorted and the mail carrier has to start out on the route as early as possible," says the inventor.

Zimmermann considered how the throughput of letters in the sorting unit could be increased, and came up with the idea of installing an automatic interim storage point that can be used in every sorting unit - for example, in a two-level sorting unit. Each level consists of a conveyor belt leading to many different compartments, into which the letters are sorted in the right sequence according to house numbers or delivery areas. There are about a hundred compartments on each level. When the system is running without the new storage module, one of the two conveyor belts is always running at less than full capacity - that is, when many letters arriving at random are primarily being directed toward the destinations of the other hundred compartments. But if all of the letters are initially stored temporarily in the storage module, they can be continuously directed toward both levels. "Thanks to the improved utilization of capacity, the system saves a lot of time in the sorting process, especially when letters are being sorted according to mail carrier routes," explains Zimmermann. This considerably improves the throughput: the initial sorting process - that is, the distribution among the major mail centers - doubles its performance, e.g. from approximately 45,000 letters per hour to as much as 90,000 letters per hour.

The storage module is powered by its own electric motor and can be easily installed in existing sorting systems. It autonomously regulates the pressure within the growing stacks of letters, so that the letters are precisely positioned. That's because the stacking process requires a different amount of pressure than the individual sorting process, for example. This regulation of pressure is a key element in ensuring the trouble-free operation of the system.

The invention can be installed at various locations in the sorting systems. In this way, mail centers can save time without having to install additional expensive machinery.

Zimmermann has been working for 23 years now on the mechanical development of sorting machines, and he has been responsible for 75 inventions as well as receiving 175 international patents. "At this point, I focus more on the overall process than on the individual elements," he says. As a system architect, he is facing up to a major challenge of his sector: to structure processes with increasing effectiveness without having to resort to expensive additional hardware.

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