1843, American physicist Alexander Bess invented the fax machine according to the pendulum principle. 1850, christopher baker Weil in the United States began to replace Alexander Bain's pendulum mode with "roller and screw" device, which made fax technology take a step forward. 1865, Iranian Abakatri made a practical fax machine according to the principle put forward by Bain and Bakewell, and conducted fax communication experiments among French cities such as Paris, Lyon and Marseille. It can be seen that fax has a history of 150 years since its invention, but its popularity has been in recent decades. Prior to this, its development was very slow, mainly limited by the use conditions and backward technology. Since 1970s, countries all over the world have opened fax services on the public switched telephone network, and fax has been widely developed. Especially in 1980s, with the progress of fax machine standardization and the maturity of technology, it became the fastest developing non-voice service. To sum up, fax has gone through the following three stages from production to development;
(1) basic stage (1843— 1972)
At present, fax machines basically adopt mechanical scanning mode, and most of them adopt roller scanning. The circuit of fax machine adopts analog technology and discrete components. In terms of transmission, low-efficiency modulation technologies such as amplitude modulation and frequency modulation are adopted, and low-speed transmission is basically carried out by using special wired circuits. At this time, the application scope of fax is also very narrow, mainly used for news and weather broadcast.
(2) Development and promotion stage (1972-1980)
Since 1969, especially after 1972, fax has entered a new historical development period compared with ITT's progress in fax standardization and the development of fax technology itself. During this period, fax technology developed from analog to digital, mechanical scanning was replaced by solid-state electronic scanning, and low-speed transmission developed to high-speed transmission. Represented by document fax machine, its appearance and popularity have changed people's traditional views on fax machines and accelerated the development of fax communication. In addition, the application scope of fax has also expanded. In addition to transmitting documents, news photos and weather maps, it is also used in medical treatment, printing, book management, information consultation, financial data, electronic post and so on.
(3) Multifunctional Stage (after 1980)
At present, fax machine is not only widely used as communication equipment, but also plays an important role in office automation system and e-mail, and will transition to a comprehensive processing terminal. Now, it has been combined with microcomputer, using computer technology to increase the functions of fax in information collection, storage, processing and exchange, and gradually incorporated into the integrated services digital network (ISDN).