How a Computer Works (2015)

25. Printer

Printer

The Printer allows a permanent record of a document or picture to be made. Like the computers monitor the image is built up from tiny dots on the papers surface. Whatever print technology is used ink-jet or laser, a matrix of ink dots are placed onto a sheet of paper or transparency.

Today most printers incorporate colour technology that allows high quality pictures to be printed on a desktop printer.

Motherboard

Data is fed to the Parallel port

Data is sent from the CPU to the GMCH chip that in turn passes it to the I/O controller hub. From here data is routed to the I/O Controller chip.

This chip passes the data to the parallel connector.

Bitmap, Outline Fonts

Bitmap

Outline Fonts

The printer accepts data from the computer in two main formats, bitmaps for the printing of images and a small number of fonts for printing text. Outline fonts are used to print a wide variety of text styles.

The printer interprets where to place ink dots on the paper page from data issued from the computer.

The Postscript format is a common type used by the printing trade.

Here the page including text is sent to the printer as a bitmap. The bitmap is a grid of dots. Outline fonts are more versatile as they allow different font sizes and styles to be printed.

Dots

Magnified

Actual Size

A printed page consists of tiny dots positioned so close together that from a distance they appear as an image.

When you print a document or picture (bitmap) the computer decides what is the best method of printing.

With a text based document the fonts used are sent to the printer. The printer reproduces the text in the specified font.

With a bitmap picture each pixel colour is sent by the computer to the printer. The printer prints each pixel as a dot.

Print Mechanism

Small rollers move the paper vertically in time with the ink-jets print head. The print head moves horizontally across the paper. In the case of a colour printer the print head consists of two cartridges. One cartridge for colour, the other provides black ink only.

Ink Cartridge

Inside the cartridge are some 50 ink filled firing chambers. Each chamber is attached to a microscopic nozzle. The nozzles are visible from the outside of the cartridge.

Each chamber has a resistor which an electrical pulse travels through and heats the ink at the bottom of the chamber.

The ink boils to a temperature of 900F. The vapour from the ink expands through the nozzle to form a droplet at the tip of the nozzle.

The pressure of the vapour bubble forces the droplet onto the paper.

Character

Ink Cartridge

A typical character is formed by an array of these drops 20 across and 20 high. As the resistor cools the bubble collapses.

This action sucks fresh ink from the attached reservoir into the chamber.