REVIEW

British postal engineeringC.E.E. Clinch, B.Sc, C.Eng., F.I.Mech.E., F.S.S., F.I.E.E.

Indexing term: Review of Progress

Abstract: There have been two major engineering conferences in London which have covered the span ofdevelopment of postal mechanisation in which the British Post Office has taken a leading part. This reviewgives the background to the decisions taken which have determined the course of postal mechanisation inthe UK. It also comments on the world scene against which these developments have taken place andhave been recorded by the papers and discussions at those two conferences spanning a decade of progress.

1 History

Posts can rightly claim an inheritance which extends overmany centuries. Scholars date the first biblical reference [1]to posts to around 1000 BC. However, the worldwide letterpost service, as we know it today, is the brain child ofRowland Hill a railway administrator whose pamphlet onpostal reform was published in 1837..The whole essence of auniform low cost, large volume usage, of posts has its roots inthe building of the railways to provide cheap, reliabletransport. Technological development is therefore the veryfoundation of postal services but the application of furthertechnology to replace the vast labour requirement of theindustry has proved a difficult problem. The majority of jobsperformed by postal staff are relatively simple for men, butcomplex for machines.

The first postal machine [2] was invented by PearsonHill, the son of the founder of the service. A steam-drivenstamp-cancelling machine was patented in 1857 designed tooperate at 50 letters per minute. A foot-operated machine wasmade at the cost of £173 (about £5000 at 1979 prices). In1859 a number of hand-operated machines with automaticinking of the stamp die were put into service.

Today it is difficult to envisage the magnitude of thechange proposed by Rowland Hill. Let us recall that it was notuntil 1853 that houseowners were first asked to provideletter slits in their house doors and in 1852 Anthony Trollopeintroduced, for the first time, street boxes for the collectionof letters. The design of such a device may seem simple, butit is fundamental decisions, on the frequency of collections,the distance between collecting points and the average lettersize, that determine the size and shape of the box and whetherit should generally be pillar mounted or small and wallmounted as is common on the continent of Europe. Most ofthe changes in design over the century have been in decorationrather than fundamental. Still today cast iron seems to be thebest material to match the requirements [3].

The design of the King Edward Building [4] in the City ofLondon included conveyor-belt systems to take mail directfrom the collecting boxes in the building front wall to thesorting-office floor and a ropeway bag conveyor. This buildingwas opened for service in 1910.

The Post Office still operates, 22 h a day, its own fullyautomatic underground railway [5] between most of theLondon main sorting, offices and main-line railway terminalstations. The installation of the underground railway wasplanned before the First World War, but was not put intoservice until 1927. The trains are driven by DC motorsoperating on a dual voltage basis, 150V along the platforms

Paper 1189A, received 29th May 1980. Commissioned IEE ReviewMr. Clinch was formerly Deputy Director of the Postal Mechanisation& Buildings Department, Craythorne House, 8-10 Newgate Street,London EC1A 7AB, and is now retired at 20 Winchester Road,Northwood, Middlesex HA6 1JF, England

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and 440V between stations to provide a good speed profile.The coaches hold mail in bags with rapid loading andunloading arrangements. Its existence relieves London roads ofthe congestion that would be caused by the additional vansthat would otherwise be required. It provides the Post Officewith a highly reliable transport system and a consistency ofjourney times that ensures despatches connect with themain-line train services.

In 1935 the world's first successful letter sorting machinewas installed in The Hague in Holland and a similar machinewas tested in Brighton, England [6]. The Transorma machine,as it was called, gave service from 1936 until 1969. Fiveoperators fed letters into clips and coded the destinationin synchronism with the machine mechanism. Experiencewith this machine had a major influence on the basic designof all future sorting machines for letters, parcels andpackets.

During the Second World War, 1939 to 1945, develop-ment of postal machinery ceased in the UK. After the warthe Universal Postal Union invited the British, theNetherlands and the Swiss postal adminstrations toco-operate in the preparation of a survey of postalmechanisation, published in 1951 [7]. The report concen-trated on conveyor systems, making only a brief mentionof the Transorma letter sorting machine, and made noreference to experimental parcel sorting machines that hadbeen constructed and tested in the UK in 1937.

2 Letter mail service

To appreciate the postwar development of letter mailequipment one must first understand the basic manual system.The volume of letters and parcels handled by the British PostOffice annually is given in Fig. 1. The volume of mailfluctuates mainly with price and GNP of the country. Com-parisons with technically advanced countries, e.g. USA,Canada and Sweden, suggests that as GNP grows mailincreases, in spite of competition from telegraph andtelephone services.

Even with the reduced letter traffic of today, on mostworking days the Post Office collects about 30 millionletters from 100000 pillar boxes and 25 000 post offices.Each individual item can be addressed to any one of the21 million UK delivery points or to an even greaternumber overseas. The majority of the letter mail arecollected at about 1700h and are required at breakfasttime the next day. The postal problem is how to get all themail transported and delivered with maximum speed andminimum cost. No items may be scrapped and damage mustbe minimal. The first steps that are clearly necessary are toturn all the letters so that they face the same way (this iscalled facing), cancel the stamp (termed franking) beforesorting into despatches. In the manual system the sizeof letters, and the reach of an average man, means that at

0143-702X181/020107 + 10 $01.50/0 107

any one sorting operation, the selection is usually one outof 48. Some countries use semicircular fittings and someoffices have additional boxes set at an angle to the mainframe to increase the selections. With 48 box fittings aminimum of five sorting operations are necessary to providethe one out of 21 million selections needed (48 to thefourth power gives only about 5 million). In practice not allboxes can be used for inland distribution for various reasons,in particular the need to match selections to actual despatchesto be made. Usually each letter passes through 12 pairs ofhands and part of the address is read seven or eight times

63 65 67 69 71 73 75 77 79

1959 61 63 65 67 69year

75 77 79

Fig. 1 Volume of mail by year

a Lettersb Parcels

between collection and delivery. This sorting work was spreadover 1200 offices in the UK; the number of offices throughwhich any one letter passes depends upon its origination anddelivery points and will vary from one to five. Postal lettermechanisation is aimed at automating as many of theseprocesses as possible and to reduce the manpower need of theindustry.

3 Letter preparation

In large offices the bags of mail collected from the street pillarboxes are emptied on to a rising conveyor belt which isintended to provide a fairly uniform flow of mixed packetsand letters into a machine called segregator. Throughout theworld a number of techniques have been tried for segregation,air-jets, rotating brushes and vibrating surfaces, but none haveproved more successful than the British Post Office inventionof the rotating drum of slats [8—10]. The drum is set at anangle of 6° to the horizontal and is about 2 m in diameter.The slats forming the drum are arranged with a 6.35 mm (? in)gap between them so that letters of less thickness than thisfall through and other items travel the length of the drum andare collected at the lower end.

As the drum rotates the slat gap is automatically enlargedwhen the slat is at the top of its travel to release trappeditems. Fig. 2 shows the view into an operating segregateddrum. The letters that account for about 90% of the pillar boxcontents are taken away on a conveyor belt and transported,on edge, up an incline so that they turn on to their long edges.Oversize letters, i.e. those more than 140 mm (5.5 in) wide, areseparated from the POP (Post Office preferred) main letterstream. The POP letters are divided into short and long lettersto aid bundling for subsequent handling.

Fig. 2 Packet output of drum segregator

The stacked letters are then passed to an ALF, automaticletter facing machine [11-14]. Automatic linking betweensegregator, ALF and other machines in the mechanisedhandling chain can be provided. Operational experience hasindicated that the linked arrangement lacks flexibility tohandle varying traffic flows and reduces reliability since all orno machines operate if all are automatically linked. The ALFsearches for the stamp and turns all letters so that the stampsmay be cancelled automatically and, assuming the normalrelationship between stamp and address is held, then theyare ready for address reading and sorting at the next stage. Themachine automatically stacks separately letters bearing a singlestamp to the value of the lowest second class fee.

To enable the machine to function a ready means is neededto distinguish the stamp from other writing or print on theitem. The items include picture postcards which pose aproblem. Some machines do operate by optical detection andsome countries, Japan for example, limit the colour of theirstamps to facilitate this [15]. Stamps have been marked formagnetic detection. At one time graphite lines were printed onthe stamps and the surface resistance was measured betweentwo probes with 1000V PD applied. Fluorescent markingcannot be used successfully because chemical whiteners areincorporated in most paper used for envelopes and addresslabels. The British Post Office has developed a special organicresin ink which has phosphorescent properties for stampmarking [16—18]. By irradiating the envelope with ultravioletlight, and then looking for the after-glow from the stamp100—200 ms later, a stamp printed with this special ink maybe readily detected.

The cost of postage is kept to a minimum when the assetsof the postal business are used continuously. These assets arestaff, buildings and equipment. The requirement for improvedbusiness efficiency is to have indicated which mail needsimmediate attention and which can be held over to smooth thework flow. To enable this to be achieved the Post Office,which always had various mail categories, e.g. printed paperrate, gave the public the option of the lower rate for a slower

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service. For the machines to take advantage of this it wasdecided that the second class minimum letter rate stamp(11 | p at the current time) would be printed with a single barof phosphorescent ink and all other stamps would have twobars or all over wash of phosphorescent. The ALF machinesearches each corner of each letter and tests to see if there is asingle bar of phosphor. The machine, after cancelling thestamp, stacks separately those with a single minimum valuestamp, others with stamps and those without any stamps, e.g.airmail, business reply envelopes. A manual operation at alatter stage extracts the second class letters having more thanone stamp. In the absence of any phosphor, optical scanning isused to detect and correctly orientate letters with official paidand business reply symbols.

In smaller offices the complexity of the segregator and ALFmachines is not justified and a simpler device, a facer-cancellertable [19] is used. The incoming mail is emptied from the bagson to a long table in front of which up to ten postmen canstand. Above the table is a shelf and conveyor belt for packets,which runs to the men's left, and along the front edge of thetable are two conveyors running to the right. Each of thelower conveyors feed a stamp-cancelling and letter-stackingunit. Postmen manually segregate and face the letters andplace packets on to the higher belt conveyor, and put firstclass letters on one of the front belts, and second class ontothe other. The machine thus provides a means of automaticallycancelling and stacking separately first and second class letters.

4 Letter sorting development

As mentioned earlier, the Transorma [5] machine operatedsynchronously, i.e. the machine determined the runningspeed — not the operator. If a man was not able to maintainthe machine speed, or if the mail was difficult to read, eitherselection opportunities were missed or sorting accuracy wasreduced. After the war, design commenced on a six operatormachine selecting into 120 boxes working asynchronously,i.e. each operator could work at his own speed. For the firsttime mail was automatically presented to the operator; hedid not have to pick up each letter out of a pack. The machinewas large and complex because of the need to interleave thework from the six operators. At that time, the controlequipment was based on cold-cathode valves and spread over15 racks.

In 1950 work started on the construction of 20 single-position letter-sorting machines (SPLSM) [20]. Each machinewas individually controlled. It sorted into 144 boxes at amaximum speed of 7200 letters per hour, i.e. six times fasterwith three times the number of selections possible withmanual working. The operator had letters presented to him sothat he could see two letters at a time, one above the other. Inthis way he coded one while reading the next to be coded. Hehad to remember the sorting plan and used a key pad foreach hand, 12 keys on each. A later version of these machines[21] using integrated logic circuit controllers is still used forsorting overseas mail.

The use of such machines for all sorting would provedifficult, particularly for sorting at the office of delivery wherethe operator would need to remember a code number for eachdelivery walk. The 12 x 12 keyboard was then replaced by astandard typewriter keyboard, and an electronic translatorusing a ferite core matrix memory was provided. Thispermitted the operator to type an 'extract code' to determinethe selection. This extract code comprised the first two andthe last two letters of a name plus the initial letter of the typeof throughfare. (E.g. London Road was keyed as LO ON Rand Wellington Street became WE ON S.) Such codes are notunique and so physical checks had to be made beforedespatch. These developments improved the efficiency of

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working but did not overcome the problem that the addresshad to be read by man at each sorting stage.

About 1960 it was decided to aim to the goal that eachaddress should be read only once and the envelope markedin a machine-readable way for all subsequent operations. Thefirst proposal for a machine-readable code was that a verticalline of green dots should be printed on the envelope, but thiswas rejected by the administration and invisible marking wasrequested. It was therefore decided to use a phosphorescenttechnique as used for stamp tagging. Since, at times, the codemarks may be on top of the stamp or very near to the stampedge two different phosphors are used. Phosphorescentmaterials exist that respond to radiation at different wave-lengths. A material will, however, always react to a higherenergy signal. The phosphor used for the code marks willrespond to radiation at 254 nm wavelengths but not to365 nm, whereas the phosphor used for the coding dots willreact to 365 nm and to shorter wavelengths, includingradiation at 254 nm. Now that phosphor dot coding has beenused for some time, the postal administration have asked thatthe code be made visible to the human eye. They want thepublic to be more readily aware that mechanisation is beingused and they want postman to be aware of reused envelopes.Clearly, if an envelope has been coded once, the application ofa second code can only cause confusion. A blue dye istherefore to be added to the ink mix to achieve this withouttoo much reduction in the afterflow level.

Whereas the UK has concentrated on the development ofphosphorescent marking inks and printers for the applicationof code marks, a number of overseas administrations haveintroduced fluorescent bar code marking [22, 23]. Thefluorescent marking has the advantage that it is easier to printat high speed (most fluorescent inks are true solutions whereasmany phosphorescent inks are particulate granules in a liquidsuspension). The reading of fluorescent code marks, is,however, less reliable, possibly by a factor of ten times.Phosphorescent code marks have been printed mostsuccessfully at rates of up to 7000 items per hour by atechnique similar to a typewriter in that the luminescentmaterial is carried on a tape which is pressed against theenvelope by a hot pin. This hot-press transfer technique, is notpractical for higher speeds, however, recent developments ofprinters and inks seem to have solved this problem [24]. Oneof the main problems on the road to development of suitableinks has been that many phosphors themselves, or theirsolvents, have been toxic and the search has been for materialsthat are safe for the public and for operators and maintenancestaff to handle.

Because operators can only read and code letters at speedsof around 2000 letters per hour whereas machines can sortletters at rates up to 30000 letters per hour, it is obviouslyeconomical to separate the coding operation from the sortingfunction. The first practical solution to the printing ofmachine readable code marks was the introduction of codingdesks into Luton in 1959. The operator was presented withtwo letters at a time, one above the other. He read the address,keyed in a code, which was transhted into binary form, andcode dots were printed on the envelope face.

5 Letter Post Plan

At the same time as the first coding desks were beingdesigned, a plan was generated to make a completelymechanised postal system for the handling of letter mail andnot just the addition of mechanical aids to postal work. Theproposal was for a new network, initially of 120 offices andlater reduced to 82 main sorting offices, to be establishedon to which all letter sorting was to be concentrated; theseletter mechanisation offices would interchange mail directly

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and in bulk, only the sorting work directly related to thedelivery walk would be retained at the 1600 offices used forthe manual system. The delivery-walk sorting has to be doneby the local man for only he knows the idiosyncrasies of thehouse numbering schemes, the problems of road crossing andcan optimise his walk for a given day's distribution of letters.

A computer program was written to simulate, in financialterms, the new plan so that the benefits of the concentrationplan could be assessed. It is obvious that to concentrate allsorting on to one centre may minimise sorting cost, butmaximise transport cost, and, at the other extreme, amaximum number of offices would not minimise transportcosts since vehicles would not be fully loaded. It was possible,with the computer program, to investigate a range of practicaloptions and, based on this the decision taken, to have 83mechanised offices to handle most of the letter mail.

6 Postcodes

The experience with extract coding and, accepting the need tohave a postcode that would minimise postal costs by making itquicker to machine mark mail, it was agreed to introduce anational postcoding scheme. Postcodes were not new. TheLondon districts were established in 1856 and later dividedinto areas to give the familiar London Wl and so on. Anumber of countries abroad, the USA in particular, introducedthe zip code, an all-number code, for sorting to their posttowns. The Medical Research Council were asked to advise onthe form of a code that would permit sorting down to apostmans walk. They reported that a mixed letter and figurecode would minimise the number of digits needed and reducethe error rate of coding. The most common error in telephonedialing is known to be the reversal of digits in the numberbeing recalled, e.g. 64501 is dialed as 65401. This type oferror is considerably reduced with mixed alphanumeric codes.The Post Office chose, based on this advice, a code in twoparts, e.g. AB1 7BC, giving adequate capacity. The first part isusually sufficient to identify the concentration office to whichthe letter is sent and as far as possible the letters used are amnemonic for the town name (e.g. AB = Aberdeen CR =Croydon). The second part is about one twentieth of apostmans walk. This provides sufficient flexibility to enablewalks to be adjusted with changes of traffic from the buildingof new houses, flats and offices. Not all possible lettercharacters are used to minimise confusion arising betweencharacters such as 0 and Q, K and R, M and N, I and 1, V andU. It later proved difficult to adhere to the six character codeor the rigid division between the two parts of the code. Thereare now some five- and some seven-character codes in additionto the standard six format [25]. With hindsight, it is regrettedby some engineers that more redundancy was not included inthe coding scheme to improve the accuracy of sorting,especially as we work toward direct automatic reading ofpostcodes which will be described later.

Canada has followed the UK lead [26] but in generalother overseas administrations have followed the Americanall-number code arrangement. In most countries the numericpostcode is only sufficient to direct mail to a posttown. Thisdepends on the size of the country, of course. In Sweden afive-digit code is sufficient to break down the sorting to anindividual street, whereas five digits in Japan give only a townor area of a city. This limitation of code capacity is a majorproblem. The local sorting is often the most difficult since itis easier to find staff who know sufficient geography to knowthe location of the posttowns but more difficult to get staffwho know the local area with sufficient detail. This is anincreasing problem when sorting has to be carried outremotely from the delivery point. Many overseas adminis-

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trations are now belatedly trying to extend their codingsystems.

Thus, although it seemed inconsistant that, at the timewhen the telephone business was removing letters from thetelephone dial, posts introduced a mixed alphanumberic code.The problems are different. A telephone dial is limited toabout ten digits; a 26-hole dial would have been a bit big. Alsothe use of letters in the London linked numbering schemebecame a limitation as the number of usable letter codes wasless than the required number of 10000 line-switching units.Neither of these factors affected posts.

7 Coding desk development

The first generation of coding desks [26—28] was designed forthe operator to see two letters presented vertically and to keythe postcode. The key operations were translated into two12-bit binary codes and printed with a start mark and a parity-check bit as two lines of phosphorescent dots along the lengthof the envelope. Fig. 3 shows a typical arrangements of addresscode marks. The first three characters of the code are denotedby the lower row of dots and the second three characters bythe upper row. Once the operator has coded one letter he canpreview the next letter presented in the window above. Ittakes considerable practice to gain speed at coding, but, withthe preview facility, speeds in excess of 2000 per hour canregularly be achieved.

If no postcode is written on the envelope the operator canuse an extract-code principle explained in Section 4 and thetranslator will convert the first three and the last two letters ofthe posttown into the correct outward code so that thebottom row of dots can be printed. In this way the lack of apostcode does not necessitate the letter being diverted intoa separate stream for manual handling at all future stages. Itdoes, however, slow down the operator since he has to changefrom the mechanical process of directly copying the postcode,and prevents the second line of code being printed at thisone reading of the address. It would be possible for the sortingoffice at the distant end to use an extract code of thethoroughfare name for the inward sorting operation but this isnot usually justified; the letter is handled manually at thereceiving end.

In 1973 a second generation of coding desks was designed[29, 30]. The major change was to simplify the mechanicalpresentation. Letters on the second-generation desk arepresented in-line moving from right to left. This minimises theoperator's eye movements since the letter travels in the normalreading mode and permits previewing of more than one letter.

second code group

Mr A Black30 Crown StreetABERDEENAB1 2HD

r

* * \ '

start point

coding-deskreference

first code group

Fig. 3 Typical address code marks

IEEPROC, Vol. 128, Pt. A, No. 2, MARCH 1981

This has a particular advantage when handling mail to acommon address, e.g. pools coupons and credit-card payments.This design has, as well as minimising the letter-movingmechanisms, reduced the noise level and gives a low profiledesk improving the environment for the operators generally.

Fig. 4 shows a second-generation coding desk in operation.The speed of the travel of the letters is dependent upon theoperators keying rate and they are therefore unpaced. Toprevent the operator being confused as to which letter is beingcoded, a light strip along the bottom edge of the presentationbelt indicates which is the letter being coded.

8 Code Translators

With the telephone system 'directors' are used to translatethe digits dialed into the routing instruction for the call.Similarly, the postcode, or extract code keyed by theoperator, has to be translated into a suitable form to printthe codemarks on the letter. At a later stage in theoperation the codemarks read by the sorting machines haveto be translated into operating, instructions to activate thediverters to route the letter to the correct box in that machine.Since 1950 there have been a number of devices used for thesetranslation processes [31 —34]. The library of information hasbeen variously stored on magnetic core matrices, optically onfilm wrapped around a drum, on magnetic drums, withinstandard computer programs and in translators in integrate d-circuit shift registers [35].

The choice of storage and control equipment is governed byboth the cost of the electronics and the operational needs. Thetranslation of the postcode into binary code marks is notidentical at all offices but is reasonably consistent. Additionaltranslations have to be made as new premises demand serviceand there are deletions as the result of building demolitionsand changes of function. The translation from codemarks intomachine operating instructions needs to be varied frequentlyand sometimes a complete revision is required. To fully usethe sorting machines most have four sorting plans to whichthey are switched throughout the day, i.e. a machine may besorting to London districts for 2 h and then changed to dealwith local delivery or up-country despatches to ensure that themail meets the evening train departure schedule. Withvariations of traffic flow over the years, including the effect ofopening new mechanised concentration offices, a completerevision is required. To meet these needs the latest translator isprogrammed in such a way that revised sorting plans can beaccommodated by rewriting software programs at postal head-quarters by postal staff who need not be professionalcomputer programmers.

Fig. 4 Second-generation coding desk

Reliability of the translator equipment is vital. As thereis only one translator serving each office its complete failurewould stop the work of all the coding desk operators and allthe sorting operations. To overcome the problem that IC shiftregisters lose the information stored in them if the main powersupply fails, the latest translator has a floppy-disk back upwhich enables the library information to be reset in about 1.5min. This also provides a ready means of introducing newsorting plans. The floppy-disk can be up-dated off-line and fedinto the operational equipment at a convenient time.

The advances in electronics have reduced the real costs oftranslation, reduced its physical size and improved itsreliability. With time it could be economical for each machineto have its own inbuilt translator. This would save thecomplication and cost of the interleaving of demands from thevarious machines on the common unit and save the cost of thehighways linking the machines.

9 Video coding desks

An alternative to the second-generation coding desk describedin Section is to use closed-circuit television (CCTV)techniques. The coding operator can sit in a quite office-typeroom with a video display linked to a television camera. Theletters are passed in front of the television camera which, withthe codemark printer, is housed on the sorting office floor. Byusing CCTV correctly the mechanical transport of the letterscan be minimised thus improving the overall reliability.

An experimental installation of video coding desks wasmade in Norwich sorting office in 1975 [36] and has beensuccessfully used to investigate various methods of display andoperating procedures [37]. Similarly, trial installations havebeen made abroad, in particular, in Germany [38] in Berlin.Compared with the British second-generation equipment, theimprovement in the environment for the video-coding-deskoperators did not outweigh their disadvantages. The dis-advantages of video coding desks are, first, that they are moreexpensive, as the simplification of the mechanical handlingplant was less than the cost of the television equipment, and,secondly, that the lack of direct contact with the mail hampersthe operators. If an envelope is difficult to read, the video deskoperator cannot change the viewing or lighting angle toovercome glare. If there is any reason for taking a letter out ofthe stream this can only be done by the video desk operatortelephoning the sorting office floor for someone else tointervene. There may, however, be conditions when videocoding techniques are justified, for example, if extensivebuilding costs could be avoided by having remote coding and,in future, if it were an adjunct to provide manual interventionto overcome difficulties in an otherwise automatic address-reading system (see Section 10). A paper study has beenprepared to form the basis for future experimentation withvideo coding desks [39]. This mathematical approach could beused for the next phase of development of this equipment.

10 Machine reading of addresses

The wartime development of computer technology andcode breaking by pattern recognition techniques launched aserious research programme into the problems of designingmachines to read addresses. Initially the research centred onthe reading of individual typed or printed characters. Beforemachines could be used the wider problems, of determiningwhich printing on the envelope was the address to which theletter was to be sent, had to be solved.

At the commencement of the research, electronic memorywas costly compared with the situation today and the studieswere therefore directed toward the reading of a wide range oftype fonts relying on the minimum amount of stored

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information. Optical character recognition, which has to copewith a wide range of colour contrasts between type andbackground colour and ideally an indefinite number of printand type fonts, was therefore slower to develop for postalapplications than for equipment for other uses such as bankcheque readers. For bank cheques a standard format ofcharacters was agreed and quality of paper and print colourtightly controlled. A recognition system suitable for postaluse was developed by the British Post Office [40] based onmachine learning techniques. The machine recognitioncomputer system was presented with a large number ofcharacters and the parameters of recognition were auto-matically built up within the machine. The biggest difficultyproved to be not in the basic recognition of any character butto determine which marks on the paper were to be analysed ascharacters. The tendency for letters to touch, or to be joinedby extraneous blemishes, made it difficult to isolate eachcharacter to offer to the recognition process.

The optical character-recognition techniques invented inthe UK have been further developed [41] and modified toovercome the basic problems. The research has concentratedon the reading of the postcode. There are areas of the envelopewhere the address is unlikely to be. The machine can scan andfind the bottom right group of characters in the address andthis should be the last three characters of the postcode. Fromthese characters the height and width can be assessed, thesize and colour contrast normalised and the character convertedinto a matrix of 16 x 24 picture points. This matrix can beoperated on mathematically to provide statistical estimates ofthe likely character. 40 such estimates are made using lineartransforms of the 16 x 24 matrix and a weighted estimate isautomatically determined of the most likely character. Theactual weights used can be determined by a machine learningprocess.

A useful address-reading machine consists of more than theelectronic analysis system. To improve the economicefficiency of any machine it must, in general, handle thetraffic as fast as possible, although there is an upper limit onspeed if there is insufficient mail of the right type to be fedto it. The design aim for the UK machine was 27 000 items perhour. To read addresses at this speed requires a transportsystem which will destack letters and move them past areading head at about 2m/s. A lighting and optical readingsystem that will operate at this speed and, if the machine isnot directly coupled to a sorting machine, a printer is requiredto codemark the envelopes with phosphorescent dots at fasterthan 100 per second. The solution to the mechanical, opticaland printing problems proved to demand a major effort fromthe research team.

Today there is available a range of equipment that can readcharacters with a sufficient reliability to enable them to beused for mail address reading [15, 42, 43] . Most advancedcountries have machines on trial. Overseas development startedlater than in the the UK and has taken advantage of thereducing cost of electronic memory and, because in manycountries the postcode only aids sorting to posttown, theyhave had to include the capability of reading one or two linesof the address as well as the postcode. It is clear that accuracyof sorting to the posttown is of major importance because anitem sent to the wrong town is delayed by a day or two to getthe mistake corrected. A letter to the wrong postman in theright town can be correctly delivered on the same day. Thelack of redundancy in postcodes has forced many countriesinto developing machines that read posttown as well as thepost code to improve the reliability of the reading systems.

Japan has a number of machines operating that read theirnumerical five-digit postcode and typed, printed or hand-written numerals can also be read [44]. These machines are

coupled directly to sorting machines, but they have nocapability to do the sorting that is equivalent to the secondhalf of the UK postcode. America and Canada have a numberof machines reading postcodes and printing a bar code influorescent ink. In a number of European countries there areexperimental installations of address reading machines printingcodemarks in either normal black or fluorescent ink.

The next stage in the development of address readingequipment in the UK will be to put on trial a machine with acapability of reading posttown and or county name as well asthe post code. The machine has to check for consistencybetween the outward part of the postcode and the town orcounty and print the full set of code marks in a phospho-rescent ink if the post code has proved readable; the lower lineof code marks where the posttown only can be determined. Itseems that in the future most machines will rely more onanalysis of the complete system of the letters and words readrather than any further improvement in the reliability ofreading individual characters. The reading of handwritten postcodes and addresses is highly likely, and may prove lessdifficult than the initial steps into type and print reading.

11 Letter sorting machines

Once the decision had been taken to code mark letters itfollowed that letter sorting machines would change from theoperator controlled machines described in Section 4. Suchmachines would not be limited by the operative's speed ofreading and coding. Initially, the specification for a sortingmachine operated by the reading of codemarked mail was tosort at 7200 items per hour into 144 boxes. The early cold-cathode register control system was replaced by a 'pin-wheel'memory device [45]. The pin wheel consists of a steel wheelaround the rim of which is a series of accurately dimensionedholes parallel to the hub. In each hole a steel pin is fitted witha good sliding fit. Solenoids are arranged so that the pins canbe pushed in to indicate the code when the code marks areread, as the letter enters the sorting section, and feelers detectthe moved pins causing the divertors in the machine to routethe letter to the right box. At the end of the cycle the pins areall reset mechanically to the normal position. Pin-wheelmemories have to be accurately made and maintained andthey have a limited speed of operation; although this was notinconsistent with the speed necessary for the mechanical partsof the rest of the machines of that time. To increase the

• operating speed of automatic letter sorting machines there hasbeen developed an electronic control unit based on standardIC microprocessors, and with improved mechanical partsmachines can now sort at rates of up to 20 000 items per hour.It is possible to drive machines faster, but only with increasedrisk of damage and sorting error.

The choice of 144 selections for British Post Office designscontracts with the greater flexibility of overseas-designedmachines. In many countries machines have 300/400selections and operate at speeds of up to 30000 items perhour. The more numerous the selections the bigger themachine and the greater the difficulty of accommodatingthem in existing buildings. Furthermore, the 144-selectionmachine is usually associated with a presorter. The presortermakes an initial breakdown into four or five divisions whicheffectively provides for up to 700 selections. It is also possibleto use more than one box for any selection that is heavilyused, by suitable control arrangements, thus providing theflexibility of use required by the postal administration.

12 Parcels

The mechanical handling of parcels poses a completelydifferent set of problems to the handling of letters. First,

112 IEEPROC, Vol. 128, Pt. A, No. 2, MARCH 1981

there is no need to segregate parcels into different streams.The possible speed of handling is much lower for parcelsbecause of their weight, size and shape. Also, address readingof labels that are stuck on uneven surfaces or tied on isextremely difficult. The randomness of parcels is often notrealised outside the mail handling business. Mention of a fewitems that have been seen on one conveyor belt in a parcelsorting office may indicate the spread. A cylindrical box ofcinema film, a pair of pheasants tied by the legs, walkingsticks, a diesel tractor crown wheel and a hat box are notinfrequent rarities. The British Post Office parcel serviceoperates in competition with other goods carriers and handlesabout one third of the parcels in the UK. This comprises only2% of the total mail items handled, but weighs about the sameas the other 98%, i.e. about 450 0001 a year carried by eachservice. The definition of a parcel has varied with time. In the1960s the upper limit was 15 lb (6 kg), this has been increasedto 10 kg (221b) and overseas parcels can be up to 20 kg.Already the UK 10 kg limit has been extended, by agreement,for a percentage of bulk postings and this limit may be furtherextended. The greater the range of material handled, thebigger is the possible market for the business and the greaterthe difficulty of handling mechanically without damage.

Successful parcel sorting machines were installed in Englandin the Paddington sorting office in 1936. This comprised aseries of moving openable buckets. The operator slid a parcelinto a bucket and pressed a code button which set thedischarge point of the bucket along the line of the sortingmachine. Similar machines were installed in Leeds in 1959 andLondon's Western District Office in 1965. An experimentalmachine using trays was tested in Bristol. At that time parcelswere sorted at 1200 offices in the UK and a large office madeup to 500 direct despatches to other offices.

In the late 1960s a parcel-post plan was formulated for theBritish Post Office which proposed to concentrate parcelsorting in about 30 offices and to fully mechanise thesecentres. At about the same time Australia had a tilted-beltparcel sorting machine in successful operation and it wasdecided to make such machines the basis of the parcelmechanisation programme. A tilted-belt PSM [46] is shown inFig. 5. It comprises a single continuous-belt conveyor which ishorizontal at the end where the parcels are fed on and coded,the belt is twisted so that it runs at an angle of 37° to thehorizontal across its width along the remaining length of themachine. A steel side wall, which is hinged in sections; runsalong the lower edge of the belt. The parcels travel with thebelt and slide against the side wall. At the required dischargepoint, determined by the keyed in code, the wall is loweredand the parcel slides off the belt down a chute to a despatchpoint or for further sorting.

Since only 30 selections are required these can beremembered by the postman and no translation facility isprovided. The operator remembers the route for the dispatchesand presses a single key making the one out of 30 selections.The control mechanism of the machine registers the selectionnumber. Clock pulses are derived, from the belt drive, to timethe travel of the parcel along the machine. When the parcelposition reaches a discharge gate the coded number iscompared with the gate number and if it coincides the gate isactivated. To save wear the gate is not closed until the machinedetermines that the following parcel does not want the sameselection. A variety of control mechanisms are used for parcelsorting machines including the pinwheel similar to thatdescribed for the earlier letter sorting machines. Modernequipments use IC shift registers.

A number of developments have taken place in machinedesign in the UK. Some have been mechanical modificationssuch as the treating of the steel sidewall to unify the friction

necessitated by the increased use of plastics for wrappingparcels. The machines have an inherent sorting capability ofabout 4000 parcels per hour although one man, even if fedwith parcels that are in line and with the addresses correctlyfaced, can only sort at about 1200 parcels per hour. Multiple-feed arrangements have been developed that permit the workof more than one sorter to be handled on each machine [47].Multiple feeding complicates both the mechanical arrange-ments at the input to the machine and the control equipmentto ensure correct interleaving of the codes keyed.

The tilted-belt machine has been extensively used overseasas well as in the UK. There are now 24 offices equipped withabout 70 PSMs in British Post Office use. Many Europeancountries have favoured a tilting-slat machine [48]. Thismachine comprises a driving chain drawing along a line of slats,each about 75 mm broad, any number of which can be tiltedto discharge a parcel carried on them at the required dischargepoint. Such machines have more mechanical parts than thebelt machines and were initially noisy. Recent developmentsand selection of materials, have reduced the noise andimproved the general performance of this type of machine.It has a greater flexibility of use in that it can easily bearranged to tilt either way to discharge parcels on to eitherside of the machine. An experimental installation is to bemade in England at Redhill for operational assessment. Thisoffice is particularly suited to the application of the tilted-slatdesign in that the traffic can be handled on one machine andmore selections can be provided in the limited space in theexisting building.

The practice is to take all received parcels in bulk to a highpoint in the building, to carry out primary sorting at thatlevel and then to use gravity by bringing parcels down chutesin the multiple streams to the despatch positions. Initially, allparcels were transported in the ubiquitous mail bag. Bags werebrought to the office by road or rail and, since 1953, chainconveyors have been provided to carry the mail into andaround the buildings.

13 Chain conveyors

Mail handling uses chain conveyors [49, 50] differently fromthe usual chain conveyors for factory production lines. Thespeed of chains in a sorting office is usually two or three timesfaster; the length of the chain is usually longer and the routemore complex and the load applied is irregular in the sortingoffice. The incoming bags of mail are hooked on to the movingchain and discharged at any one of a number of locations inthe office depending on whether the bag contains letters,registered packets, parcels etc. The normal method ofdetermining the discharge point for a bag is by mechanically

Fig. 5 Tilted-belt parcel sorting machine

IEEPROC, Vol. 128, Pt. A, No. 2, MARCH 1981 113

setting code pegs on the bag carrier and detecting the codesetting at each possible discharge point. Coding systems havebeen used, as with belt conveyors, in that the code is writteninto an electronic memory, the bag carriers are timed andmoved along in shift registers in sympathy with the physicalmovement along the chain and release signals are initiatedfrom the electronic controllers.

Considerable development has taken place over the pastdecade to improve chain-conveyor reliability and reduce thenoise caused by the rattle of the chain components in the steeltrack. These measurements have led to the mathematicaldistribution of tension along chain conveyors with multipledriving points has been carried out with continuouslyrecording stress guages fitted to the moving links and thetrack. These measurements have led to the mathematicalprediction of chain and track stresses to permit improvementin office design. Recent operational requirements in a newoffice designed for Hong Kong could not have been metwithout this recent work.

14 Wheeled containers

Mail bags hold, on average, five parcels and considerablenumbers of man hours are spent in tying and labeling eachbag. With the development of the parcel concentration planlarge numbers of parcels are exchanged between the 30mechanised offfices, and so it was economically advantageousto replace the bags with wheeled containers [52, 53]. Thecontainers are designed to fit modularly into standard road,rail and freightliner vehicles. They each hold about 100parcels and can be emptied automatically, with the minimumdamage, at either floor level or raised to the sorting-positionlevel and fed direct to the parcel sorting positions. The liftand tip machine [49] has been fully developed by theBritish Post Office and installed at a number of offices.

15 Chute design

Parcels leaving the sorting machines are discharged from thetilted belt and need to be delivered to the despatch ornext sorting position at a controlled speed. The angle of thechute must ensure light parcels do not stop part way downand heavy parcels do not decend so fast as to cause damage atthe bottom of the descent. Using Monte Carlo statisticalcalculations it has been possible to formulate a spiral chutecrossection that ensures constant speed of discharge. LondonUniversity undertook the study [54] for the British PostOffice. A new chute profile has been produced and made inglass-reinforced fibre, coated with a special plastic facing, withexcellent results and at a lower cost than the traditional steelchutes. An alternative approach to the problem has beentried in Australia [55] using a driven sidewall to a spiral chute.However, the higher cost and lower reliability of such amachine reduces its likelihood of general introduction.

16 Packet sorting

Packets are defined as nonstandard items in the letter mailservice and are generally referred to in the postal business asunmachinable mail. In spite of this definition there have beena number of attempts to build packet sorting machines for allor part of the packet handling.

The standard machine used for packet sorting in the UK[56] comprises a series of 36 boxes arranged in a 9 x 4pattern repeated along a line (see Fig. 6). The boxes areopen at the top and can be discharged by opening doors atthe bottom. Sorters toss the packets directly into the boxes

Fig. 6 Packet sorting machinethus making a 1 out of 36 selection. The opening sequence isso arranged that when the content of box 1 in the first groupof 36 has just passed the bottom of box 1 in the second groupof 36 it is discharged on to one of four belt conveyors whichrun under the line of boxes. In this way, at the end of thebelts the packets for each destination are taken off together.The greatest difficulty with this machine is with the sorting oflarge flat items. These tend to float when tossed and ofteneither fall into the wrong box or lie fiat on the box edges.In Australia a special sorting machine was developedspecifically for handling large flat items. This was called a'slit sorter' as the envelopes were posted into slits andconveyed on edge. An experimental installation in MountPleasant in London did not prove successful.

In Toronto Canada a new approach has been tried forpacket sorting using what is termed a 'gull's wing' traymachine [57]. This machine uses trays in which either wingmay be dipped to discharge the packet to left or right of thedriving chain. It is claimed that with this machine packets aresorted at 24 000 per hour into 111 selections. 14 operatorsfeed the machine and type in postcodes as with the lettersorting machine.

17 Maintenance control

It is desirable to monitor the performance of all machines insuch a way as to detect incipient fault conditions, i.e. beforethe service is affected. This is not always possible but wherewear mechanisms are understood it is often possible to devise:tests that will detect the wear at an early stage. Much of theletter and parcel handling machines are equipped withperformance monitors which are coupled into a dedicatedcomputer with a teletype printer to give maintenanceinformation [58—60]. Records are automatically made ofmail flows so that the computer can provide error rates ofuncoded letters, parity-check failures, letters dischargedinto overflow boxes etc. Every 100th letter from a codingdesk is scanned to check the quality of the code marks and,because it searches between the dots to determine the signal-to-background ratio of the coding, the computer automaticallychecks if any phosphorescent material has been smudged intothe gaps. A number of other machine checks are made and theresults can be printed out on request or at routine intervalsas needed.

In addition to the computer-based test equipment all thesorting offices are provided with CCTV so that controllingofficers can monitor, from a central point, all the mail flowsand likely trouble spots. Mimic diagrams indicate whichmachines are operating and radio paging is provided to callmaintenance staff quickly to deal with faults.

114 IEEPROC, Vol. 128, Pt. A, No. 2, MARCH 1981

18 Sorting-office design

The provision for the postal service with engineering servicescannot be limited to the machine alone. There is necessaryco-operation between machine designers and operation workplanners to determine layouts and numbers of machines andthe subsequent heating, ventilation and lighting needed in theoffice. A lot of planning and installation control problemshave to be overcome before any office is completed and readyfor service [61—63]. The British Postal Consultancy Servicehas provided support on postal mechanisation schemes inmany countries abroad. The Oslo Central Sorting Office inNorway [64] is one such scheme.

The design of the office's electric light and power serviceshas to be integrated with the architects work for new buildingsand includes lifts and escalators for the movement of staff aswell as goods. The building is usually occupied continuouslyand canteen facilities have to be provided including fishfryers, pie makers, chip makers and other kitchen equipment.The reliability of these machines is often more important tothe postal staff than the complicated letter or parcel sortingmachines. The failure of mail handling equipment can often beovercome by reverting to manual methods where as failure ofkitchen equipment may cause staff to walk out.

19 Security

The UK postal business has an overnight cash holding in excessof £100 m as well as an unquoted value of negotiable pieces ofpaper including stamps, postal orders and various licences. Thisholding is in various supplies depots and scattered among the25 000 public offices. Naturally little publicity is given to theengineering development effort that ensures the safe handlingand holding of cash. No burglar alarm system can be devisedthat someone else cannot find a way to defeat. Thus thedevelopment of alarm systems is a continuous process ofchange. Electronic development has obviously played its fullpart in improving the security protection. Most safes andstrong rooms are now fitted with time-controlled locks so thatthe key holder can hand over a key knowing that it isineffective until normal staffing hours. Opinions change as tothe benefit of immediately making a loud noise locally orquickly alterting the police without giving a local alarm. Bothsystems have been developed and are in operation. Thesecurity development unit has increasingly provided alarmsystems by radio since the great train robbery. With theincrease in terrorist activities, the improvement of sensors fordetecting packages containing explosives has been accelerated.

20 The future

The above survey indicates the wide range of electrical,electronic and mechanical engineering being employed by theUK postal business and the development over the past decade.The next decade may see even greater changes. The expansionof electronic message cervices in industry and the home willprovide both competition and new opportunity for the long-standing mail services.

The past indicates that frequent threats to mail services donot often mature as expected, e.g. both telephones andtelegrams were initially hailed as an immediate replacementfor the letter service. In high technology countries such asUSA and Sweden telephone penetration and usage is high butthere has been no decline in the demand for the mail service.The type of mail often changes, for example, to include moreadvertising material as the GNP of a country rises, but thedemand for the service still exists.

Much of the UK mail contains information affecting cashtransfer i.e. either bills, invoices or payments. The introduction

of credit cards may change the mail flow but in fact hasprovided a large demand for cash payment statements to thecard organisers central computer installations. The exchangeof data in the form of punched or magnetic tape has openedup a Datapost service which is expanding.

Electronic mail, Prestel and other inventions will bechallenges for future postal engineers. I am confident that newtechnology will be used as the basis for further expansion ofengineering for the mail services in the same way as the steamrailway launched the worldwide mail services of today.

21 Acknowledgments

The author wishes to acknowledge the work of the staff of theBuildings and Mechanisation Department of Posts who havewillingly helped in preparing this review and checking themanuscript. Also to thank Mr Ian Barr, Director of theMechanisation and Buildings Department for his permission topublish the review and to use the Post Office official photo-graphs to illustrate it.

22 References

1 The Holy Bible, 1 Kings, Chap. XXI, 82 DE JONG, N.C.C.: 'Progress in postal engineering part 1: A general

survey', Post Off. Electr. Eng. J., 1970, 63, pp. 65-703 CUTMORE, N.: 'Development of pillar box 1852-1969'. I. Mech.

E. conference on British postal engineering, Nov. 1970, paper 241970

4 PETTIT, E.W.: 'The new general post office (KEB)', Post Off.Electr. Eng. J., 1968, l,pp. 165-169

5 NEW, G.W.: "The post office railway'. I. Mech. E. convention onautomatic railway, London, Sept 1964

6 GEMMEL, W.T.: 'The Transforma letter sorting machine', Post Off.Electr. Eng. J., 1936, 29, pp. 16-22

7 'Mechanical handling of mails in large sorting offices' (UPUPublication, 1951)

8 HILLS, E.G.: 'Segrating: operational requirements and development'.I. Mech. E. Conference British postal engineering, May 1970,paper 7

9 TOTTEY, S.T.: 'Segration and grading machines for letter mailhandling', Ibid., May 1970, paper 40

10 COPPING, G.P., and MYERS, T.R.: 'Mechanisation of initial stagesof processing mail part I, segregation of various classes of mail',Post Off. Electr. Eng. J., 1960,52, pp. 286-289

11 COPPING, G.P., GERARD, P.S., and ANDREWS, J.D.: 'Mechanis-ation of the initial processing of mail Part 2, Automatic facing andcancellation', ibid. 1960, 53, pp. 12-20.

12 ADAMS, G.F.: 'Letter facing machines, development and design ofproduction machines'. I. Mech. E. conference on British postalengineering, May 1970, paper 41

13 COPPING, G.P.: 'Automatic letter facing'. Ibid., May 1970, paper17

14 WICKEN, C.S.: 'Control systems for automatic letter facingmachines'. Ibid., May 1970, paper 18

15 NAKANO, H., GENCHI, H., and KIRUNO,H.: 'Recent developmentof automatic mail. Processing systems in Japan'. I. Mech. E.Conference on progress in postal engineering, Nov. 1979, paperC246/76

16 FORSTER, C.F.: 'Phosphorescent code marks in automatic letterfacing and sorting machines', Post Off. Electr. Eng. J., 1961, 54, pp.180-185

17 HARRISON, J.C., RICKARD, E.F., FORSTER, C.F., WALKER,A.D.: 'Preparation properties and application of luminescent organicresins for letter facing, classification and address coding'. I. Mech. E.Conference on British postal engineering, May 1970, paper 4

18 AGATE, M.S.: 'Assessment of the performance of phosphor postalitems'. Ibid., May 1970, paper 23

19 HILLS, E.G.: 'New mechanical aid for the smaller sorting office'.Ibid., May 1970, paper 37

20 COPPING, G.P., and BEAK, K.L.A.: 'A single operator letter sortingmachine (introduction and experimental machine)', Post Off. Electr.Eng. J., 1958, 5, pp. 104-108

21 LANGTON, H.J.A.: 'A single operator letter sorting machine (theproduction machine and future development), ibid., 1958, 51, pp.112-116.

22 FRITZ, T.: 'The coding of letter mail'. I. Mech. E. Conference onprogress in postal engineering, Nov. 1979, paper C247/79

IEEPROC, Vo. 128, Pt. A, No. 2, MARCH 1981 115

23 SAINSBURY, J.A.: 'Letter mechanisation in the Canada PostOffice'. Ibid., Nov. 1979, paper C245/79

24 HARRISON, J.C., and WICKEN, C.S.: 'Address code indexation -methods and materials'. Ibid., Nov. 1979, paper C 248/79

25 ANDREWS, J.D.: 'Coding principles and practices'. I Mech Econference on British postal engineering, May 1970, paper 12

26 WHITTINGTON, K.W.H.: 'Letter presentation'. Ibid., May 1970,paper 21

27 KNOWLES, S.C.: 'A development of a letter coding desk'. Ibid.,May 1970, paper 22

28 HEWETT, J.W., and MACKETT, R.G.: 'Code marking of lettermsaT.Ibid.. May 1970, paper 38

29 EVANS, D., HILLS, E.G., and WICKEN, C.S.: 'An easy-view lettercoding desk1, Post Off. Electr. Eng. J., 1978, 71, pp. 70-75

30 HILLS, E.G., EVANS, D., and MORRIS, F.J.: 'A second generationletter coding desk and associated equipment'. I. Mech. E. conferenceon progress in postal engineering, Nov. 1979, paper C252/79

31 ANDREWS, J.D.: 'A code translator for letter sorting machines',Post Off. Electr. Eng. J., 1959, 52, pp. 199-205

32 ANDREWS, J.D., and BELCHER, P.L.: 'Time-shared code trans-lators for letter sorting equipment', ibid., 1962, 55, pp. 173

33 PILLING, T.: 'letter post automation', Control, 1964, 8, pp. 349-353,412-471

34 GOODISON, H.: "Threaded core translators'. I. Mech. E. conferenceon British postal engineering, May 1970, paper 9

35 PHILLIPS, K.H.C., and BENNETT, H.A.J.: 'Postcode and sortingtranslation systems'. I. Mech. E. conference on progress in postalengineering, Nov. 1979, paper C239/79

36 GREATHEAD, T.W., and BUSBY, J.L.: 'Electro optical devicesused in postal mechanisation'. I. Mech. E. conference on electrooptical devices, May 1974

37 BUSBY, J.L., and FLETCHER, J.H.: 'A study of methods ofaddress presentation using experimental CCTV letter mail codingequipment'. I. Mech. E. conference on progress in postal engineering,Nov. 1979, paper C250/79

38 FRITZ, T.: 'Video coding installation'. Ibid., Nov. 1979, paperC249/79

39 MORGAN, D.: 'On the use of simulations in postal mechanisationresearch'. Ibid., Nov. 1979, paper C251/79

40 COOMBS, A.W.M.: 'On the reading of postal codes by machine'. I.Mech. E. conference on British postal engineering, May 1970, paper13

41 FLEMING, J.F., and VICKERS, J.D.: 'British post office postcodereader coder'. I. Mech. E. conference on progress in postalengineering, Nov. 1979, paper C256/79

42 STRINGA, L.: 'Survey on OCR'. Ibid., Nov. 1979, paper C253/7943 BLUCHER, R.: 'Address reader'. Ibid., Nov. 1979, paper C255/7944 MURA, T., TSUKAKOSHI, N., and TSUKUMO, J.: 'Study of hand

written numerals for OCR (recent development of bi-functionalOCR)'. Ibid., Nov. 1979, paper C254/79

45 GILES, B.E.: 'Mechanical sorting of coded and uncoded mail'. I.Mech. E. conference on British postal engineering, May 1970, paper15

46 CASTELLANO, E.J.: 'Tilted belt parcel sorting machine'. Ibid.,May 1970, paper 6

47 HENLY, H.R.: 'Progress in parcel sorting'. I. Mech E conference onprogress in postal.engineering, Nov. 1979, paper C241/79

48 HOEGH, C: 'Parcel sorting now and in the future'. Ibid., Nov. 79,paper C240/79

49 SMITH, W.J.: 'Chain conveyors for the transport of mail bags'. I.Mech. E. conference on British postal engineering, May 1970, paper43

50 KEAL, F.: 'Overhead chain conveyors'. I. Mech. E. conference onprogress in postal engineering, Nov. 1979, paper C244/79

51 GOODISON, H.: 'Recent development in chain conveyors, con-tainer handling and chutes'. Ibid., Nov. 1979, paper C243/79

52 CLINCH, C.E.E.: 'Containers for transporting mail', Post Off.Electr. Eng. J., 1968, 62, p. 20

53 STATFORD, J.M.: 'Containerisation for parcel and bulk mail in thepost office'. I. Mech. E. conference on British postal engineering,May 1970, paper 5

54 WARDLE, F.: 'The dynamics and genralised design of parcel chutesystems'. Ph. D. thesis, Queen Mary College, London, 1974

55 BRADDELEY, A.H.: 'Constant speed decent devices'. I. Mech. E.conference on progress in postal engineering, Nov. 1979, paperC242/79

56 BRACKSTONE, R.L.: 'Packet sorting machine'. I. Mech. E. con-ference on British postal engineering, Nov. 1970, paper 28

57 SMITHE, O.D.: 'Packet and parcel sortation in the Canada PostOffice'. I. Mech. E. conference on progress in postal engineering,Nov. 1979, paper C233/79

58 ANDREWS, J.D., BENNETT, H.A.J., and PRATT, A.D.: 'Letteroffice computerised monitor - LOCUM', Post Off. Electr. Eng.J., 1972, 65, pp. 172-176

59 PHILLIPS, K.H.C.: 'Performance monitoring in mechanised letteroffices'. I. Mech. E. conference on progress in postal engineering,Nov. 1979, paper C238/79

60 HENLY, H.R.: 'A system for collection and presentation of manage-ment data in parcel sorting offices'. Ibid., Nov. 1979, paperC237/79

61 GERRARD, P.S.: 'Project system planning'. I. Mech. E. conferenceon British postal engineering, May 1970, paper 33

62 CUMMINGS, F.G.: 'The Birmingham new parcel and letter sortingoffice'. Ibid., May 1970, paper 34

63 EDWARDS, D.C., and DICKIE, W.: 'Design and construction of theLiverpool Head Post Office'. I. Mech. E. conference on progressin postal engineering, Nov. 1979, paper C234/79

64 MALDE, B.S.: 'Oslo central sorting office'. Ibid., Nov. 1979, paperC231/79

116 IEEPROC, Vol. 128, Pt. A, No. 2, MARCH 1981