A sampling of printers and fax machines.
In pre-computer days, there were machines called "manual typewriters" which produced alphanumeric symbols on plain paper with no need for power cords or batteries. Invented in 1867 by Christopher Sholes, these early machines were mechanical nightmares with a profusion of pivots, levers and keys. The mechanical complexities were so profound that a proficient typist could outpace the response of the machine. In an effort to slow the fingers of these early typists, a deliberately awkward placement of the keys, the "QWERTY" format, was developed.
As years passed, the machines became more responsive, and more efficient keyboard designs were developed. Included in these variations are the Dvorak keyboard, designed by August Dvorak and patented in 1936. This configuration places the most frequently used letters in the center for use by the strongest fingers. Compared to the QWERTY arrangement, finger motions and awkward strokes are reduced over 90%. Another variation, the Maltron keyboard, varies the height of the keys, places frequently used keys under the strongest fingers and assigns up to eight keys for the thumbs. Today, relatively skilled user can type 50, 60 or even 100 or more words per minute.
The computer, and in particular word processing programs, almost, but not totally, brought an end to the typewriter--even to electrified versions. The output of early computers was directed to typewriter-like printers that responded to digital commands. The need for more speed led to daisy-wheel and dot matrix printers. Requirements for still greater speeds, quieter operation and improved letter quality evolved into ink-jet and bubble-jet printers. But the final break with ink, either as a liquid or on a ribbon, awaited the invention of the laser.
THE LASER PRINTER
The output of semiconductor lasers can be focused and easily controlled by an input signal. In a typical application, digital data from a computer is used to turn the laser output on and off. The tiny beams of light are reflected from a moving mirror and scan a rotating photosensitive drum. A latent image, invisible to the eye and composed of positive electrical charges, is formed on this drum. A fine black powder carrying a negative charge, the toner, is applied to the drum. The toner adheres only to the parts of the drum carrying the latent positive charges. Paper carrying a strong positive charge is fed past the drum, attracting the toner. The toner is fused to the paper using heat, the surface of the drum is cleaned and the process is repeated for the next page.
The laser printer brings several significant advantages to the printing process. Included are high resolution 600 x 600 dpi and greater, fast printout (can exceed 20 pages per minute) and quiet operation.
THE FACSIMILE MACHINE
Facsimile communication has been a reality for over 150 years. Alexander Bain, a Scot clock maker, made a machine capable of transmitting crude images for short distances over a telephone wire. Digital technology has replaced Bain's slow, analog approach, and the ubiquitous facsimile machine is found in almost every commercial establishment, be it the corner gas station or the neighborhood 7-11 Store.
The basic telecopier capability of the fax machine is achieved by incorporating elements of an optical scanner, a sophisticated communications system, a printer and a computer into a package that can weigh as little as 10 lb. Throw in a falling list price, the ability to copy documents, answer the phone, act as a traffic manager and function as the "front-end" of an optical character reader, and the reasons for the popularity of fax machines becomes obvious. It is just a matter of time before someone incorporates a coffee brewer into the fax machine and declares it a complete office staff.
The first step in the normal fax process is to translate the material to be transmitted into binary code. Alphanumerics, as well as pictures or signatures, are treated as graphics and must be scanned into the machine. This process is distinct from the fax-modem, an addition to a computer, which does not incorporate a scanning process. The fax-modem accepts and transmits both alphanumeric characters in American Standard Code for Information Interchange (ASCII) or graphical images which have previously been scanned and converted into binary files. ASCII is a standard which uses a seven-bit code to represent 128 decimal numbers. The numbers from 0 to 127 are assigned to letters, numbers, punctuation marks and the most common special characters.
The communication portion of the facsimile process now comes into play. Where telephone systems are incapable of dealing with digital transmission, digital data must be placed on commercial telephone lines using a modem. A modem, acronym from "MOdulate-DEModulate," converts the digital data back into analog form for transmission over the phone lines. This cumbersome process resembles the best efforts of a Rube Goldberg cartoon: (a) an analog key on a keyboard is struck which produces a digital string, which (b) is translated by the computer into (c) a graphical (analog) character on a sheet of paper. (d) A scanner transforms the graphical image into a digital string, which (e) is converted by a modem into an (f) analog signal (varying voltage), which is placed on a telephone line. The signal arrives at (g) the modem of the receiving fax machine, where it is converted into (h) a digital string and eventually printed (i) in analog form on a piece of paper or on the screen of a monitor.
Despite this Byzantine complexity, most of the processing is behind the scenes, invisible to the user. Except for occasionally overhearing of the digital "noise" characteristic of the high-speed data flow, the process is a marvel of efficiency.
The future of the fax seems very bright. Modem speeds are continually increasing and transmission protocols are becoming more widely accepted. The Consultative Committee on International Telephony and Telegraphy (CCITT), organized by the United Nations, has generated international communications recommendations which are frequently adopted as standards. CCITT recommendations extend to interfaces, modem characteristics and data networks. Rapidly coming on-line is the Integrated Services Digital Network (ISDN). Telephone companies are currently adopting ISDN, which is designed for the transmission of digital data. This system will allow faster error-free fax operation.
THIS MONTH'S SAMPLING
This month's sampling of militarized printers and facsimile machines is divided into two sections. Whereas a fax machine will contain some printing ability, the converse is not true.
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|Publication:||Journal of Electronic Defense|
|Date:||Nov 1, 1994|
|Previous Article:||Mission data development, analysis and storage.|
|Next Article:||Taking the measure of EW's effectiveness.|