How Do Thermal Fax Machines Work?
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Fax Machines Send and Receive Data
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To be considered a fax machine, an office appliance must be capable of creating, sending and receiving facsimiles of original documents. This requirement exists regardless of the printing technology used. When a document is scanned in by the machine, a digital scanner in the fax machine converts the original document into an electronic representation much like a digital picture. A modem in the fax machine modulates the digital image into sound that can be transferred across a telephone line, connects to a remove fax machine, and transmits the modulated digital image. When a fax machine receives a fax, it receives the incoming audio data from the remote machine, demodulates (using the modem) the incoming audio into machine-useable data and sends the data to the built-in or connected printer.
Thermal Printers Use Thermal Paper
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When a thermal fax machine receives and demodulates an incoming transmission from a remote fax, it must print out a copy of the original document. Thermal fax machines use an older--but still effective--technique to accomplish this task that involves specially coated paper. Thermal fax machines are loaded with a special paper that usually comes wrapped in a large roll. As faxes are received, a small motor in the fax machine feeds paper from the roll over an electronic print head. Circuitry in the fax machine that contains the demodulated electronic copy of the original document sends electrical signals to the print head. These signals cause the print head to heat up in a pattern that matches a line of the original document. As the thermal paper passes over the heated print head, a chemical coating in the paper reacts with the heated portions to produce a copy of the original document or image. This process is repeated with different portions of the print head heated, for each line in the original document or image. When the entire document has been reproduced, the fax machine's motor ejects a small portion of the thermal paper so it can be easily torn away.
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Some Thermal Fax Machines Use Plain Paper
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Although thermal fax machines that rely on thermal paper are nearly synonymous with the idea of faxing, newer thermal fax machines use a technological advancement that eliminates the need for special paper. These machines receive and demodulate incoming data in the same way as their more archaic cousins but rely on a special thermal film to transfer the faxed document onto plain paper. As each line of data is decoded from the incoming fax machine and sent to the print head, a chemically coated film passes between the print head and the paper. When the thermal print head applies heat to the film, the heat from the print head transfers a small amount of resin or wax to the paper. Motors in the fax machine advance the paper one line at a time, and the process is repeated for each line of the original document. If the document contains several pages, the sending fax machine encodes a "page break" command for each new page. The receiving machine automatically ejects the completed paper and starts printing on a new, blank sheet each time it decodes one of these commands. When printing is complete, the machine uses its paper feed motor to eject any remaining portion of paper, then returns to an idle state to await the next fax.
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