Date: Wed, 25 Nov 1998 20:27:17 -0500 From: Nicholas Bodley Subject: Re: Friden Flexowriter (I was also a Flexowriter tech, but on only very few machines.) I once owned an early IBM typewriter, with a worm-gear drive for the power roll, and a variable-speed governor-controlled motor. Used some Flexowriter parts to refurb. it. It had a 3-wheel rotary escapement; the code bar scheme was very different in detail from that of the Flexowriter. There's a very-nice image of a Flexowriter online at http://www.wins.uva.nl/faculteit/museum/flexowriter.html This university can do conversions among obsolete media; I'd really love to visit. They also have an EAI electronic analog computer. Flexowriters were frequently custom-built, and custom-coded. The encoding from keyboard to tape was fairly easy to change; the reverse, from tape to keyboard, was much harder. They were exceptionally rugged and solidly-built machines; as *manual* typewriters, if properly maintained, I'd say they'd last a few centuries (opinions, Frank?). The platen and power roll had relatively short lives, and the carriage return clutch and tape would eventually wear, too. For computers, they were the "console typewriters" of choice before Teletypes, but considerably more costly and rugged than the Model (33?) Teletype. (I used a Model 43 (iirc) Teletype, and loved it.) Because the Flexowriter was built around a super-rugged electric typewriter, you couldn't type on the keyboard without printing. The mechanical encoding matrix was operated by the same mechanisms (cams and power roll) that operated the typebars. Mechanical encoding, from ~40 typebars into ~6 bits (or more) of binary code is very easy and straightforward. The decoding is much more interesting, and "harder". Punching a tape on a Flexowriter made quite a racket. The typewriter part was an impact printer, and the punch mechanism was noisy as well. The Justowriter, which Frank mentioned, was usually a pair of special Flexowriters. The first created a specially-encoded paper tape with embedded codes to tell the other machine how much to stretch or compress a line to create an even right margin. The other machine had a double reader (two read heads). One head read the justifying codes from the tape, which were at the end of text characters for the line. Justifying codes were stored in control relays; the succeeding codes were read by the other head to obtain the the text for the line. One special Flexowriter (the LCC, for Line Casting Control) created paper tapes for Linotype and Intertype automatic typesetters. It had a carriage tension of (iirc) 22 lbs (10 kg), and a four-wheel proportional spacing escapement. There was an extra gearbox between the carriage rack and the escapement pinion. The margin stop was "micro-adjustable." There was a light on the front, above the keyboard, which signified that the typesetting machine would be able to cast the line successfully. These pushed the technology, and were quite costly. Apparently, the chief inventor for much of the Flexowriter-specific technology was Edward Blodgett, in Rochester. Definitions (and a little bit of explanation) Key: What your finger pushes down (as on a calculator). Keytop: surface your finger presses against (at least) Keylever: support for the keytop. (If it's a straight piece, as on many calcs, it's a "keystem". Flexowriters didn't have keystems.) Typebar: what swings the type "slug" toward the ribbon and paper. The Typebar contacts the "ring", which stops it really suddenly. In something like 50 microseconds, the type slug "overshoots" as the typebar bends, to squeeze the ribbon against the paper, and springs back out of contact. The rebound probably makes it return much faster than if the ribbon and paper provided the "bounce". Type alignment, according to what I read long ago, involves positioning every type slug on the end of the typebar (soldered, fairly sure) in all 6 degrees of freedom (3 rotational, 3 translational (straight-line movement)). It's a skilled art. The old fellows referred to "ring and cylinder" adjustments; the "cylinder" was the platen. People who think the keys hit the ribbon are uninformed. Typebars jam; key[lever]s don't. Paper-tape lore: ================== There were two kinds of paper tape, chad and chadless. Afaik, all Flexowriters punched only chad-style. "Chad" is the collective term for the two sizes of tiny disks punched out of the tape to make the holes. There were, quite literally, bit buckets! (Chadless tape punched out little flaps instead of complete holes. Mechanical reader pins would push the flaps out of the plane of the tape (usually upward). However, photoelectric readers couldn't read chad tape (unless somebody used an air blast...) Ordinary paper tape was a rather sniff stock, often colored pink. It was precision-slit, the widest (ordinarily) being 1 inch (~2.5 cm) wide, fairly sure. This size could accommodate 8 data channels (grouped 3 and 5 on either side of a sprocket-hole channel, for the drive sprocket. There were also 5, 6, and 7-channel devices; this was generally before ASCII; there were ooooodles of mutually-incompatible codes. For rugged duty, there was a tape (I remember a light blue) made of a paper/Mylar/paper sandwich. I've heard of tape with a layer of aluminum foil, but don't remember much about it. The pink and blue tapes were oil-impregnated to lubricate the punch pins, which were made to very close tolerances. The lubricant had a characteristic, not unpleasant (to me!) odor. The Teletype Corp. (IIrc) made some paper-tape message buffers for the USAF; these had chadless punches running from blank rolls ~3ft. (~1 m) in diameter. (Blank rolls were typ. 10" dia., maybe). The readers had swiveling heads, and the punches had clearance beyond the punch dies, so that the reader could advance itself along the tape as it read the tape, until it was aligned with the character after the one being punched. If a sudden burst of traffic came in, the reader might swing away from the punch until the device it was feeding could read the tape. Have forgotten, but there was some sort of provision for fairly large amounts of slack punched tape to drop down between the punch and reader. It was a paper-tape FIFO. Soroban Engineering (Melbourne (?), Fla.) made very high-speed punches (400 char./sec) with very interesting synchronous mechanisms; Flexowriter punches were ~35 char/sec (? Frank?) max.) and asynchronous. (Flex. punched as soon as you told it to; Soroban gave you the timing, and you had to feed it pulses derived from their timing to drive its magnets.) Soroban also made readers and punches for very wide tape. Have forgotten, but I'm reasonably sure they made 40-channel devices. Philco had a photoelectric paper tape reader (1960) that could read 1,000 char./sec and *stop on the stop character*; that means the tape was stopped with the character that told the reader to stop, still aligned in the read head. It took a very fancy, probably highly-pulsed electromagnetically-actuated clamping plate to do that, and also a fancy sprocket-drive scheme. (It might not have used sprockets; might have been rubber rollers.) The tape wasn't torn or damaged, either. The cabinet was the size of a fridge. I also saw an experimental paper-tape reader that drove a loop maybe 15 ft. (~5 m) long; had a drive wheel about 1 foot (~30 cm.) in dia. running at 3,450 r/min; tape is 10 char./inch. I eventually hope to write about Flexowriter innards is some detail; I really mustn't forget to check with Frank! (Frank, if you want to write in detail, by all means, do; don't think about waiting for me!) |* Nicholas Bodley *|* Electronic Technician {*} Autodidact & Polymath |* Waltham, Mass. *|* ----------------------------------------------- |* *|* The personal computer industry will have become |* Amateur musician *|* mature when crashes become unacceptable. --------------------------------------------------------------------------