18 June 2009

Fax machine

The invention: Originally known as the “facsimile machine,” a machine that converts written and printed images into electrical signals that can be sent via telephone, computer, or radio. The person behind the invention: Alexander Bain (1818-1903), a Scottish inventor Sending Images The invention of the telegraph and telephone during the latter half of the nineteenth century gave people the ability to send information quickly over long distances.With the invention of radio and television technologies, voices and moving pictures could be seen around the world as well. Oddly, however, the facsimile process— which involves the transmission of pictures, documents, or other physical data over distance—predates all these modern devices, since a simple facsimile apparatus (usually called a fax machine) was patented in 1843 by Alexander Bain. This early device used a pendulum to synchronize the transmitting and receiving units; it did not convert the image into an electrical format, however, and it was quite crude and impractical. Nevertheless, it reflected the desire to send images over long distances, which remained a technological goal for more than a century. Facsimile machines developed in the period around 1930 enabled news services to provide newspapers around the world with pictures for publication. It was not until the 1970’s, however, that technological advances made small fax machines available for everyday office use. Scanning Images Both the fax machines of the 1930’s and those of today operate on the basis of the same principle: scanning. In early machines, an image (a document or a picture) was attached to a roller, placed in the fax machine, and rotated at a slow and fixed speed (which must be the same at each end of the link) in a bright light. Light from the image was reflected from the document in varying degrees, since dark areas reflect less light than lighter areas do. Alens moved across the page one line at a time, concentrating and directing the reflected light to a photoelectric tube. This tube would respond to the change in light level by varying its electric output, thus converting the image into an output signal whose intensity varied with the changing light and dark spots of the image. Much like the signal from a microphone or television camera, this modulated (varying) wave could then be broadcast by radio or sent over telephone lines to a receiver that performed a reverse function. At the receiving end, a light bulb was made to vary its intensity to match the varying intensity of the incoming signal. The output of the light bulb was concentrated through a lens onto photographically sensitive paper, thus re-creating the original image as the paper was rotated. Early fax machines were bulky and often difficult to operate. Advances in semiconductor and computer technology in the 1970’s, however, made the goal of creating an easy-to-use and inexpensive fax machine realistic. Instead of a photoelectric tube that consumes a relatively large amount of electrical power, a row of small photodiode semiconductors is used to measure light intensity. Instead of a power-consuming light source, low-power light-emitting diodes (LEDs) are used. Some 1,728 light-sensitive diodes are placed in a row, and the image to be scanned is passed over them one line at a time. Each diode registers either a dark or a light portion of the image. As each diode is checked in sequence, it produces a signal for one picture element, also known as a “pixel” or “pel.” Because many diodes are used, there is no need for a focusing lens; the diode bar is as wide as the page being scanned, and each pixel represents a portion of a line on that page. Since most fax transmissions take place over public telephone system lines, the signal from the photodiodes is transmitted by means of a built-in computer modem in much the same format that computers use to transmit data over telephone lines. The receiving fax uses its modem to convert the audible signal into a sequence that varies in intensity in proportion to the original signal. This varying signal is then sent in proper sequence to a row of 1,728 small wires over which a chemically treated paper is passed. As each wire receives a signal that represents a black portion of the scanned image, the wire heats and, in contact with the paper, produces a black dot that corresponds to the transmitted pixel. As the page is passed over these wires one line at a time, the original image is re-created. Consequences The fax machine has long been in use in many commercial and scientific fields.Weather data in the form of pictures are transmitted from orbiting satellites to ground stations; newspapers receive photographs from international news sources via fax; and, using a very expensive but very high-quality fax device, newspapers and magazines are able to transmit full-size proof copies of each edition to printers thousands of miles away so that a publication edited in one country can reach newsstands around the world quickly. With the technological advances that have been made in recent years, however, fax transmission has become a part of everyday life, particularly in business and research environments. The ability to send quickly a copy of a letter, document, or report over thousands of miles means that information can be shared in a matter of minutes rather than in a matter of days. In fields such as advertising and architecture, it is often necessary to send pictures or drawings to remote sites. Indeed, the fax machine has played an important role in providing information to distant observers of political unrest when other sources of information (such as radio, television, and newspapers) are shut down. In fact, there has been a natural coupling of computers, modems, and fax devices. Since modern faxes are sent as computer data over phone lines, specialized and inexpensive modems (which allow two computers to share data) have been developed that allow any computer user to send and receive faxes without bulky machines. For example, a document—including drawings, pictures, or graphics of some kind—is created in a computer and transmitted directly to another fax machine. That computer can also receive a fax transmission and either display it on the computer’s screen or print it on the local printer. Since fax technology is now within the reach of almost anyone who is interested in using it, there is little doubt that it will continue to grow in popularity.


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