Tuesday, 1 January 2013
When I was consulting for a small company making fluorescents, they were asked by the Royal Mail (RM) to make both stamp phosphors (SP) and coding phosphors (CP). I developed suitable chemicals for both applications.
CPs were used to produce a machine readable set of dots representing the post code of a particular letter. The original CP we produced appeared as blue dots on the envelope and these were activated by long wave UV (whereas the SP was activated by short wave). However this system has been abandoned and replaced by a bar code system using a fluorescent ink.
SPs are used to produce a machine readable set of stripes on a stamp which enables the machine to orientate the letter the correct way up (stamp top right with address approximately central) so that the written post code can be read and the correct machine readable code stamped onto the envelope. An indication of this is given in the following
There is only a small fraction of a milligram of phosphor on a stamp, and the letter bearing the stamp is passed at high speed past a bank of ultra violet (UV) lamps, which activate the phosphor. As the envelope leaves the UV lamps it is still glowing and this glow is detected by photoelectric detector which activates the next operation on that envelope (see video).
Thus the SP is a critical part of RM's sorting process, and from what I can work out RM handles about 19 billion items of post each year, about half of which use stamps, so about 10 billion pa. RM have been using the SP I developed for about 15 years, so that means 150 billion items using my SP.
There is an interesting essay on RM stamps and SPs in http://gbmachins.co.uk/html/phosphor_bands.html , which indicates the difference between first and second class stamps. The first class has two stripes of phosphor, the second one stripe. So the first class stamp will give two flashes of afterglow to the detector, which will send it to the first class channel, the second class will give one flash to the detector which will send it to the second class channel. Take this with the orientating use shown in the YouTube video and the SPs now have two machine readable functions in the sorting process
b) separation of first and second class mail
This is the work of Dr Frank Holland and must not be re produced without his permission.