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.