The bits for the scanned document travel through the phone line and arrive at a receiving fax machine. The bits are decoded, uncompressed and reassembled into the scanned lines of the original document. There are five common ways to print the fax, depending on the type of machine that receives it:
Thermal paper -- When fax machines started infiltrating offices en mass in the 1980s, most of them used thermal paper. The paper is coated with chemicals that react to heat by turning black. Thermal paper has several big advantages:
It's very inexpensive to build a thermal printer.
Thermal printers have no moving parts except for the paper-feed mechanism.
There are no expendables like ink or ribbons because the paper contains the ink.
Thermal printers are nearly indestructible.
The only disadvantage is that the paper discolors over time, and it turns completely black if you leave it in a hot car.
Saturday, August 22, 2009
Modern Fax Machines
A modern fax machine does not have the rotating drums and is a lot faster, but it uses the same basic mechanics to get the job done:
At the sending end, there is some sort of sensor to read the paper. Usually, a modern fax machine also has a paper-feed mechanism so that it is easy to send multi-page faxes.
There is some standard way to encode the white and black spots that the fax machine sees on the paper so that they can travel through a phone line.
At the receiving end, there is a mechanism that marks the paper with black dots.
At the sending end, there is some sort of sensor to read the paper. Usually, a modern fax machine also has a paper-feed mechanism so that it is easy to send multi-page faxes.
There is some standard way to encode the white and black spots that the fax machine sees on the paper so that they can travel through a phone line.
At the receiving end, there is a mechanism that marks the paper with black dots.
Basic Idea Behind Fax Machines
Fax machines have been around in one form or another for more than a century -- Alexander Bain patented the first fax design in 1843 (see Science Line: Alexander Bain & the Fax Machine to learn more). If you look back at some of the early designs, you can get a very good idea of how they work today.
Most of the early designs involved a rotating drum. To send a fax, you would attach the piece of paper to the drum, with the print facing outward. The rest of the machine worked something like this:
There was a small photo sensor with a lens and a light.
The photo sensor was attached to an arm and faced the sheet of paper.
The arm could move downward over the sheet of paper from one end to the other as the sheet rotated on the drum. In other words, it worked something like a lathe.
© Chris Hondros/Getty ImagesFax machines are frequently used to send resumes and other important papers.
The photo sensor was able to focus in and look at a very small spot on the piece of paper -- perhaps an area of 0.01 inches squared (0.25 millimeters squared). That little patch of paper would be either black or white. The drum would rotate so that the photo sensor could examine one line of the sheet of paper and then move down a line. It did this either step-wise or in a very long spiral.
To transmit the information through a phone line, early fax machines used a very simple technique: If the spot of paper that the photo cell was looking at were white, the fax machine would send one tone; if it were black, it would send a different tone (see How Modems Work for details). For example, it might have sent an 800-Hertz tone for white and a 1,300-Hertz tone for black.
At the receiving end, there would be a similar rotating-drum mechanism, and some sort of pen to mark on the paper. When the receiving fax machine heard a 1,300-Hertz tone it would apply the pen to the paper, and when it heard an 800-Hertz tone it would take the pen off the paper
Most of the early designs involved a rotating drum. To send a fax, you would attach the piece of paper to the drum, with the print facing outward. The rest of the machine worked something like this:
There was a small photo sensor with a lens and a light.
The photo sensor was attached to an arm and faced the sheet of paper.
The arm could move downward over the sheet of paper from one end to the other as the sheet rotated on the drum. In other words, it worked something like a lathe.
© Chris Hondros/Getty ImagesFax machines are frequently used to send resumes and other important papers.
The photo sensor was able to focus in and look at a very small spot on the piece of paper -- perhaps an area of 0.01 inches squared (0.25 millimeters squared). That little patch of paper would be either black or white. The drum would rotate so that the photo sensor could examine one line of the sheet of paper and then move down a line. It did this either step-wise or in a very long spiral.
To transmit the information through a phone line, early fax machines used a very simple technique: If the spot of paper that the photo cell was looking at were white, the fax machine would send one tone; if it were black, it would send a different tone (see How Modems Work for details). For example, it might have sent an 800-Hertz tone for white and a 1,300-Hertz tone for black.
At the receiving end, there would be a similar rotating-drum mechanism, and some sort of pen to mark on the paper. When the receiving fax machine heard a 1,300-Hertz tone it would apply the pen to the paper, and when it heard an 800-Hertz tone it would take the pen off the paper
fax machine
Short for facsimile machine, a device that can send or receive pictures and text over a telephone line. Fax machines work by digitizing an image -- dividing it into a grid of dots. Each dot is either on or off, depending on whether it is black or white. Electronically, each dot is represented by a bit that has a value of either 0 (off) or 1 (on). In this way, the fax machine translates a picture into a series of zeros and ones (called a bit map) that can be transmitted like normal computer data. On the receiving side, a fax machine reads the incoming data, translates the zeros and ones back into dots, and reprints the picture.
The idea of fax machines has been around since 1842, when Alexander Bain invented a machine capable of receiving signals from a telegraph wire and translating them into images on paper. In 1850, a London inventor named F. C. Blakewell received a patent for a similar machine, which he called a copying telegraph.
But while the idea of fax machines has existed since the 1800s, fax machines did not become popular until the mid 1980s. The spark igniting the fax revolution was the adoption in 1983 of a standard protocol for sending faxes at rates of 9,600 bps. The standard was created by the CCITT standards organization and is known as the Group 3 standard. Now, faxes are commonplace in offices of all sizes. They provide an inexpensive, fast, and reliable method for transmitting correspondence, contracts, résumés, handwritten notes, and illustrations.
A fax machine consists of an optical scanner for digitizing images on paper, a printer for printing incoming fax messages, and a telephone for making the connection. The optical scanner generally does not offer the same quality of resolution as stand-alone scanners. Some printers on fax machines are thermal, which means they require a special kind of paper.
All fax machines conform to the CCITT Group 3 protocol. (There is a new protocol called Group 4, but it requires ISDN lines.) The Group 3 protocol supports two classes of resolution: 203 by 98 dpi and 203 by 196 dpi. The protocol also specifies a data-compression technique and a maximum transmission speed of 9,600 bps.
Some of the features that differentiate one fax machine from another include the following:
speed: fax machines transmit data at different rates, from 4,800 bps to 28,800 bps. A 9,600-bps fax machine typically requires 10 to 20 seconds to transmit one page.
printer type: Most fax machines use a thermal printer that requires special paper that tends to turn yellow or brown after a period. More expensive fax machines have printers that can print on regular bond paper.
paper size: The thermal paper used in most fax machines comes in two basic sizes: 8.5-inches wide and 10.1-inches wide. Some machines accept only the narrow-sized paper.
paper cutter: Most fax machines include a paper cutter because the thermal paper that most fax machines use comes in rolls. The least expensive models and portable faxes, however, may not include a paper cutter.
paper feed : Most fax machines have paper feeds so that you can send multiple-page documents without manually feeding each page into the machine.
autodialing: fax machines come with a variety of dialing features. Some enable you to program the fax to send a document at a future time so that you can take advantage of the lowest telephone rates.
As an alternative to stand-alone fax machines, you can also put together a fax system by purchasing separately a fax modem and an optical scanner. You may not even need the optical scanner if the documents you want to send are already in electronic form.
The idea of fax machines has been around since 1842, when Alexander Bain invented a machine capable of receiving signals from a telegraph wire and translating them into images on paper. In 1850, a London inventor named F. C. Blakewell received a patent for a similar machine, which he called a copying telegraph.
But while the idea of fax machines has existed since the 1800s, fax machines did not become popular until the mid 1980s. The spark igniting the fax revolution was the adoption in 1983 of a standard protocol for sending faxes at rates of 9,600 bps. The standard was created by the CCITT standards organization and is known as the Group 3 standard. Now, faxes are commonplace in offices of all sizes. They provide an inexpensive, fast, and reliable method for transmitting correspondence, contracts, résumés, handwritten notes, and illustrations.
A fax machine consists of an optical scanner for digitizing images on paper, a printer for printing incoming fax messages, and a telephone for making the connection. The optical scanner generally does not offer the same quality of resolution as stand-alone scanners. Some printers on fax machines are thermal, which means they require a special kind of paper.
All fax machines conform to the CCITT Group 3 protocol. (There is a new protocol called Group 4, but it requires ISDN lines.) The Group 3 protocol supports two classes of resolution: 203 by 98 dpi and 203 by 196 dpi. The protocol also specifies a data-compression technique and a maximum transmission speed of 9,600 bps.
Some of the features that differentiate one fax machine from another include the following:
speed: fax machines transmit data at different rates, from 4,800 bps to 28,800 bps. A 9,600-bps fax machine typically requires 10 to 20 seconds to transmit one page.
printer type: Most fax machines use a thermal printer that requires special paper that tends to turn yellow or brown after a period. More expensive fax machines have printers that can print on regular bond paper.
paper size: The thermal paper used in most fax machines comes in two basic sizes: 8.5-inches wide and 10.1-inches wide. Some machines accept only the narrow-sized paper.
paper cutter: Most fax machines include a paper cutter because the thermal paper that most fax machines use comes in rolls. The least expensive models and portable faxes, however, may not include a paper cutter.
paper feed : Most fax machines have paper feeds so that you can send multiple-page documents without manually feeding each page into the machine.
autodialing: fax machines come with a variety of dialing features. Some enable you to program the fax to send a document at a future time so that you can take advantage of the lowest telephone rates.
As an alternative to stand-alone fax machines, you can also put together a fax system by purchasing separately a fax modem and an optical scanner. You may not even need the optical scanner if the documents you want to send are already in electronic form.
HOW IT WORKS:
Facsimile Transmission, or fax, communications system for the electrical transmission of printed material, photographs, or drawings. Facsimile transmission is accomplished by radio, telephone, or undersea cable. The essential parts of a fax system are a transmitting device that translates the graphic material into electrical impulses according to a set pattern, and a synchronized receiving device that retranslates these impulses and prints a facsimile copy. In a typical system the fax scanner consists of a rotating cylinder, a source projecting a narrow beam of light, and a photoelectric cell. The copy to be transmitted is wrapped around the cylinder and is scanned by the light beam, which moves along the cylinder as it revolves.The output of the photoelectric cell is amplified and transmitted to the receiving end, where a similar cylinder, covered with specially impregnated paper, revolves in synchronism with the transmitting cylinder. A light of varying intensity moves along the rotation cylinder and darkens the paper by chemically reproducing the pattern of the original.
The Fax Machine
SciTech, Carbons to Computers series from the Smithsonian Institution.The facsimile machine was invented in 1842 by Alexander Bain, a Scottish clockmaker, who used clock mechanisms to transfer an image from one sheet of electrically conductive paper to another. Bain patented the "automatic electrochemical recording telegraph" in 1843.
history of fax machine
The use of the fax machine to transmit images via telephone lines did not become common in American businesses until the late 1980s, but the technology dates back to the nineteenth century. In 1843 in England, Alexander Bain (1818-1903) devised an apparatus comprised of two pens connected to two pendulums, which in turn were joined to a wire, that was able to reproduce writing on an electrically conductive surface.
In 1862, the Italian physicist Giovanni Caselli built a machine he called a pantelegraph (implying a hybrid of pantograph and telegraph), which was based on Bain’s invention but also included a synchronizing apparatus. His pantelegraph was used by the French Post & Telegraph agency between Paris and Marseilles from 1856 to 1870.
Elisha Gray (1835-1901), American inventor, born in Barnesville, Ohio invented and patented many electrical devices, including a facsimile transmission system. He also organized a company that later became the Western Electric Company.
In 1902, Arthur Korn (1870-1945) in Germany invented telephotography, a means for manually breaking down and transmitting still photographs by means of electrical wires. In 1907, Korn sent the first inter-city fax when he transmitted a photograph from Munich to Berlin.
In 1925, Edouard Belin (1876-1963) in France constructed the Belinograph. His invention involved placing an image on a cylinder and scanning it with a powerful light beam that had a photoelectric cell which could convert light, or the absence of light, into transmittable electrical impulses. The Belinograph process used the basic principle upon which all subsequent facsimile transmission machines would be based. In 1934, the Associated Press introduced the first system for routinely transmitting "wire photos," and 30 years later, in 1964, the Xerox Corporation introduced Long Distance Xerography (LDX).
For many years, facsimile machines remained cumbersome, expensive and difficult to operate, but in 1966 Xerox introduced the Magnafax Telecopier, a smaller, 46-pound facsimile machine that was easier to use and could be connected to any telephone line. Using this machine, a letter-sized document took about six minutes to transmit. The process was slow, but it represented a major technological step. In the late 1970s, Japanese companies entered the market, and soon a new generation of faster, smaller and more efficient fax machines became available.
In 1862, the Italian physicist Giovanni Caselli built a machine he called a pantelegraph (implying a hybrid of pantograph and telegraph), which was based on Bain’s invention but also included a synchronizing apparatus. His pantelegraph was used by the French Post & Telegraph agency between Paris and Marseilles from 1856 to 1870.
Elisha Gray (1835-1901), American inventor, born in Barnesville, Ohio invented and patented many electrical devices, including a facsimile transmission system. He also organized a company that later became the Western Electric Company.
In 1902, Arthur Korn (1870-1945) in Germany invented telephotography, a means for manually breaking down and transmitting still photographs by means of electrical wires. In 1907, Korn sent the first inter-city fax when he transmitted a photograph from Munich to Berlin.
In 1925, Edouard Belin (1876-1963) in France constructed the Belinograph. His invention involved placing an image on a cylinder and scanning it with a powerful light beam that had a photoelectric cell which could convert light, or the absence of light, into transmittable electrical impulses. The Belinograph process used the basic principle upon which all subsequent facsimile transmission machines would be based. In 1934, the Associated Press introduced the first system for routinely transmitting "wire photos," and 30 years later, in 1964, the Xerox Corporation introduced Long Distance Xerography (LDX).
For many years, facsimile machines remained cumbersome, expensive and difficult to operate, but in 1966 Xerox introduced the Magnafax Telecopier, a smaller, 46-pound facsimile machine that was easier to use and could be connected to any telephone line. Using this machine, a letter-sized document took about six minutes to transmit. The process was slow, but it represented a major technological step. In the late 1970s, Japanese companies entered the market, and soon a new generation of faster, smaller and more efficient fax machines became available.
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