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Origin ofNumerical Control

George Younkin, Guest Author

Many senior citizens mayremember the playerpiano where a perfo-rated paper roll about11.5 in wide was used

to play music. As the perforations inthe paper passed over what looked likea long harmonica, various noteswould be played on the piano. In1908, the harmonica device wasmodified to have smaller holes andspaced at 9 per inch. The control waspneumatic, and thus when a group ofperforations in the paper passed over ahole in the harmonica device, pre-programmed music would be played.Of course, pinned barrels to operatethings such as clocks were used manyyears before the player piano. How-ever, the combinations of holes in thepaper roll were the equivalent of anumber scheme representing a song.The pneumatic system was operatedby foot pedals to supply a flow of air.Thus, the player piano was an earlyconcept of numerical control (for adetailed discussion of the origin ofnumerical control, see [1]).

In the BeginningIn the spring of 1949, Prof. S. Brownat the Massachusetts Institute ofTechnology (MIT) received a phonecall from John T. Parsons, vice presi-dent of the Parsons Corporation. Thisphone call was historic in naturebecause it was the beginning of theinvention of numerical control formachining [1]. Because the ParsonsCorporation did not have sufficientfinancial backing to support such alarge-scale development and did not

have the facilities or professional staff toproceed with such a large-scale project,it approached MIT to explore the possi-bility of having theU.S. Air Force sup-port this project attheMIT Servo Lab.

One of the origi-nal concepts was touse a card reader toinput information.This was found tobe too slow to keepup with the requiredcutting feeds. In thefinal design, punchedpaper tape was usedto input machinedata. As the digital controller pro-gressed, it was determined that 292vacuum tubes (mostly thyratrons) wererequired. There was much discussionabout the reliability of vacuum tubes. Inthe final design, industrial thyratronswere used.

Along the way, the Parsons Cor-poration-MIT relationship ended, andthe U.S. Air Force issued a contract on3 April 1951 to continue the researchwith the MIT Servo Lab. The entireproject was limited by the state of theart in hardware. The transistor wasdiscovered in December 1947 at theBell Laboratories. Thus, commercialuse of the transistor and other devicessuch as the silicon-controlled rectifierwere years away. In the final design,the relay storage circuitry was replacedwith magnetic core storage circuitry.

The first demonstration of thenumerical control on a Cincinnati mill-ing machine was held on 1517 Sep-tember 1952 at the MIT Servo Lab. Inthis demonstration, the control, which

was named the Director, was directlyconnected to the machine. The totalsystem was named Numericord (Fig-

ure 1). For commer-cial applications, itwould not be feasi-ble to connect anumerical Directorto every machine. Itwas at this pointthat General Elec-tric (GE) created aplayback unit to runthe machine via a1-in magnetic tape.The magnetic tapehad a reference sinu-soidal signal that

was constant. The other channels onthe tape also had sinusoidal signalsthat were phase shifted in relation tothe reference signal. The amount ofphase shift was proportional to thedesired position. The final design useda standard Flexowriter with a seven-hole paper tape for inputting machinedata to the Director (Figure 2).

Because of hardware and elec-tronic limitations, the signals had tobe recorded on the magnetic storagetape at one-quarter time rate. Thatis, it took four hours to make onehour of machine time.

Machine ApplicationsAt the outset, machine builders wereskeptical about the feasibility andreliability of controlling a machineby numbers. One company, Gid-dings and Lewis (G&L) Machine ToolCompany, decided the future of ma-chine tools and included numericalcontrol. On 20March 1953, an agree-ment was reached to initiate action toDigital Object Identifier 10.1109/MIAS.2008.927525

THE PLAYERPIANOWAS AN

EARLYCONCEPT OFNUMERICALCONTROL.

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supply a Numericord numerical con-trol to G&L. The total cost of thatproject was US$390,056. It was in-tended to have a public demonstra-tion in June 1955. However, a firebroke out in the magnetic core stor-age unit a day before the demonstra-tion. The MIT Servo Lab staff, whichinstalled the Numericord system,managed to rewire the magnetic coreswith a needle and wire for each mag-netic core. The digital coding for themagnetic core storage unit wasbinary-coded decimal. The publicdemonstration was held as scheduledon 710 June 1955. Many defensedepartment people attended thedemonstration.

The outgrowth of this situationwas that the U.S. Air Force cancelledall orders for machine tools and issuednew orders to a number of machinetool builders for new machine toolswith the Numericord numerical con-trol. G&L received an order for US$12million worth of machines.

As stated earlier, the technologyof the Numericord project was aheadof its time, but the hardware was alimiting factor. The control cards inthe Director were made of a resinmaterial and would get thicker withall the heat being generated from thethyratrons.

This caused the grommets, usedfor connecting circuits on both sides

of the printed circuitry, to open thecircuit. This resulted in untold hoursof soldering grommets. Since I hadjoined G&L to workalong with the MITServo Lab staff, Ihad the pleasure ofresoldering grom-mets all day and at-tending graduateschool at the Univer-sity of Wisconsin atnight. There weremany late-night sol-dering sessions aftergraduate schoolclasses until themorning. The prob-lemwas finally solvedbymaking a new setof printed circuitcards with a glass-basedmaterial.

Another hard-ware-based prob-lem was the unreliability of thenumerous thyratrons used in flip-flopdata storage circuits. It was necessaryto order industrial type thyratrons bythe gross. One annoying problem wasthe unreliability of the magnetic tape.This tape was acetate and very brittle.It could break, and the machine partbeing programmed had to start over.Also, the iron oxide kept coming offthe tape and clogged the record heads

on the tape recorder. Finally, the 3MCompany was contacted to find asolution. After studying the problem,

3M came back witha new 1-in-wide tapethat did not break,and the iron oxidedid not come off andclog the record heads.Since this was abrand new product,it had to be named.The 3M Companynamed this new tapeMYLAR. Thus, wehave another case ofnecessity being themother of invention.

The servo driveson the G&L skinmill were electricWard-Leonard (M/G)type dc drives in theform of GE ampli-dynes (Figure 3).

These drives were evaluated by theMIT Servo Lab staff at G&L andshowed a position loop bandwidth ofapproximately 1.5 Hz. After the suc-cessful completion of the Numericordproject, G&L convinced theMIT ServoLab staff to form their own company tosupply the Numericord system tomachine tool companies, especially theairplane builders. This new companywas named Concord Controls. JamesO. McDonough was named to headthe staff of the new company.

As time moved on, machine toolcompanies started to increase their re-search staff, and soon there was a greatdiversity in types of numerical control.

1Numericord Director and Flexowriter tape preparation. (Image courtesy ofGiddings and Lewis.)

THETECHNOLOGY

OF THENUMERICORDPROJECTWASAHEADOF ITSTIME, BUT THEHARDWARE

WAS A LIMITINGFACTOR.

2Numericord Director. (Image courtesyof Giddings and Lewis.) 11

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Two of themachine tool companies thatinitiated development of their ownnumerical controls were CincinnatiMilacron and Kearney and Trecker.Bendix Research Division produced a

numerical control in the early 1950s.At that time, there were few applica-tions of contouring machining. Becausethere was a much greater market forpoint-to-point machining, G&L decided

to initiate its own less expensivenumerical control. I had completedgraduate school at that time and wasselected to design a low-cost numericalcontrol for point-to-point machiningand drilling applications. This controlwas still primitive in hardware becausecomputers were a long way off. Nev-ertheless, this control was namedNumeripoint and was introduced atthe 1960 Machine Tool Show in Chi-cago. Being a new member of theAmerican Institute of Electrical En-gineers (AIEE), I wrote my first tech-nical paper on this control andsubmitted it to the AIEE IndustrialCommittee for review. The commit-tee promptly rejected the paper. Amonth later, the trade magazine Con-trol Engineering published the paperas a feature article. Then, the U.S.Patent Office issued me a patent(no. 3101436) on this control. Last,while working at the 1960 MachineTool Show, a well-dressed gentlemancame looking for me and announced

that he was from the AIEEand rejected my paper andwanted to apologize for notunderstanding what thepaper was about.

In time, many differenttypes of numerical controlcame into being. There was aperiod when diode logic wasused, and then there werediscrete transistor circuits,followed by integrated cir-cuits, very large-scale inte-gration (VLSI), and finallymodern computers withWindows software. The restof the development of nu-merical control is history.

After many years of dedi-cated activity in the originof numerical control, JohnT. Parsons received theNational Medal of Technol-ogy in 1985 with a presen-tation by President RonaldReagan.

Reference[1] J. F. Reintjes, Numerical Control:

Making a New Technology. NewYork: Oxford University Press,

1991.

George Younkin (gwyounkin@charter.net) is a Fellow of theIEEE. IAS

3Giddings and Lewis skin mill used to demonstrate Numericord numericalcontrol. (Image courtesy of Giddings and Lewis.)

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