Electrophotographic

Thermal Transfer

Printer

There are several methods of printing the facsimile image including electrophotographic (laser or LED), ink jet, thermal transfer and, the most popular, recording on thermal paper.

60.4.5.1 Thermal primers

Heat sensitive paper is passed over a single line thermal head having a heater element for each of the 1728 (A4) picture elements.

A typical method of operation in a thermal printer is at the start of reception to step the paper back from its normal guillotine or tear off position, so that the start of the page is under the thermal head. To avoid having a driver for each element the head may be electri­cally divided into sections for printing in a matrix. The data is latched into a section and printer in 1 to 2.5ms. When all sections of the line are printed the paper is either advanced l/3.85mm for a standard line or l/7.7mm for a fineline.

A standard line may be achieved by printing 2 identical fine resolutions lines. The print energy required is about l/4mJ per black dot, at a temperature on the paper of around 90°C. Print times of between 5ms and 20ms per line are typical, with automatic compen­sation for ambient and head temperature by varying the supply voltage or the print pulse time.

60.4.5.2 Plain paper printers

A number of technologies are available to produce the printed image on plain, office type paper. The advantages of this is that copies feel like other office documents and are generally archival.

The paper is usually in roll form to simplify machine handling. It moves through the machine with, and generally at the same rate, as a thermal transfer film. The thermal head prints in a similar way to normal thermal paper printing and the film is a donor, transferring its image to the plain paper. The thermal transfer film, collected on a take up roll, is used at the same rate as the paper and retains a negative image which may need careful handling for security rea­sons.

The facsimile printer is otherwise identical to a thermal paper printer.

A well established technology in office printers uses either a laser or an LED array to discharge a photoconductive drum for offset printing. The latent image on the drum is developed by the attraction of charged normally black toner powder. This image is transferred to a cut sheet and fixed by the combination of heat and pressure at the output rollers.

The additional hardware required for a facsimile machine is bulky, expensive and significantly increases the size and cost. The paper, normal copier type paper, is much cheaper than thermal paper but when allowing for toner, drum replacement and other consumables this saving is much reduced.

Дата добавления: 2015-03-31