Different types of printer with their function and working principle.

A printer is an electro-mechanical device which converts the text and graphical documents from electronic form to the physical form. Generally they are the external peripheral devices which are connected with the computers or laptops through a cable or wire lessly to receive input data and print them on the papers. A wide range of printers are available with a variety of features ranging from printing black and white text documents to high quality colored graphic images

Quality of printers is identified by its features like color quality, speed of printing, resolution etc. Modern printers come with multipurpose functions i.e. they are combination of printer, scanner, photocopier, fax, etc. To serve different needs there are variety of printers available that works on different types of technologies.

There are basically two types of printer Impact and Non-impact printers. The printer which has physical contact between printing head and paper are called impact printer and which has no physical contact are known as Non-impact printer.

1. Dot Matrix Printers

It is a popular computer printer that prints text and graphics on the paper by using tiny dots to form the desired shapes. It uses an array of metal pins known as print head to strike an inked printer ribbon and produce dots on the paper. These combinations of dots form the desired shape on the paper. Generally they print with a speed of 50 to 500 characters per second as per the quality of the printing is desired. The quality of print is determined by the number of pins used (varying from 9 to 24).

The key component in the dot matrix printer is the ‘printhead’ which is about one inch long and contains a number of tiny pins aligned in a column varying from 9 to 24. The printhead is driven by several hammers which force each pin to make contact with the paper at the certain time. These hammers are pulled by small electromagnet (also called solenoids) which is energized at a specific time depending on the character to be printed. The timings of the signals sent to the solenoids are programmed in the printer for each character. The printer receives the data from the computer and translates it to identify which character is to be printed and the print head runs back and forth, or in an up and down motion, on the page and prints the dots on the paper.

2. Inkjet Printer

Inkjet printers are most popular printers for home and small scale offices as they have a reasonable cost and a good quality Inkjet printerof printing as well. A typical inkjet printer can print with a resolution of more than 300 dpi and some good quality inkjet printers are able to produce full colored hard copies at 600 dpi.

An inkjet printer is made of the following parts:

• Printhead – It is the heart of the printer which holds a series a nozzles which sprays the ink drops over the paper.
• Ink cartridge – It is the part that contains the ink for printing. Generally monochrome (black & white) printers contain a black colored ink cartridges and a color printer contains two cartridges – one with black ink and other with primary colors (cyan, magenta and yellow).
• Stepper motor – It is housed in the printer to move the printerhead and ink cartridges back and forth across the paper.
• Stabilizer bar – A stabilizer bar is used in printer to ensure the movement of printhead is précised and controlled over the paper.
• Belt – A belt is used to attach the printhead with the stepper motor.
• Paper Tray – It is the place where papers are placed to be printed.
• Rollers – Printers have a set of rollers that helps to pull paper from the tray for printing purpose.
• Paper tray stepper motor- another stepper motor is used to rotate the rollers in order to pull the paper in the printer.
• Control Circuitry – The control circuit takes the input from the computer and by decoding the input controls all mechanical operation of the printer.

Similar to other printers, inkjet printers have a ‘printhead’ as a key element. The printhead has many tiny nozzles also called as jets. When the printer receives the command to print something, the printhead starts spraying ink over the paper to form the characters and images.  There are mainly two technologies that are used to spray the ink by nozzles. These are:

• Thermal Bubble – This technology is also known as bubble jet is used by various manufacturers like Canon and Hewlett Packard. When printer receives commands to print something, the current flows through a set of tiny resistors and they produce heat. This heat in turn vaporizes the ink to create a bubble. As the bubble expands, some of the ink moves out of the nozzle and gets deposited over the paper. Then the bubble collapses and due to the vacuum it pulls more ink from ink cartridge. There are generally 300 to 600 nozzles in a thermal printer head which can spray the ink simultaneously.
• Piezoelectric – In the piezoelectric technology, a piezo crystal is situated at the end of the ink reservoir of a nozzle. When printer receives the command to print, an electric charge is applied to the crystal which in turn starts vibrating and a small amount of ink is pushed out of the nozzle. When the vibration stops the nozzle pulls some more ink from the cartridge to replace the ink sprayed out. This technology is patented by Seiko Epson Corporation.

3. Laser Printer

Laser printers are the most popular printers that are mainly used for large scale qualitative printing. They are among the most popularly used fastest printers available in the market. A laser printer uses a slight different approach for printing. It does not use ink like inkjet printers, instead it uses a very fine powder known as ‘Toner’. Components of a laser printer is shown in the following image:

The control circuitry is the part of the printer that talks with the computer and receives the printing data. A Raster Image Processor (RIP) converts the text and images in to a virtual matrix of dots. The photo conducting drum which is the key component of the laser printer has a special coating which receives the positive and negative charge from a charging roller. A rapidly switching laser beam scans the charged drum line by line. When the beam flashes on, it reverses the charge of tiny spots on the drum, respecting to the dots that are to be printed black. As soon the laser scans a line, a stepper motor moves the drum in order to scan the next line by the laser.

A developer roller plays the vital role to paste the toner on the paper. It is coated with charged toner particles. As the drum touches the developer roller, the charged toner particles cling to the discharged areas of the drum, reproducing your images and text reversely.  Meanwhile a paper is drawn from the paper tray with help of a belt. As the paper passes through a charging wire it applies a charge on it opposite to the toner’s charge. When the paper meets the drum, due to the opposite charge between the paper and toner particles, the toner particles are transferred to the paper. A cleaning blade then cleans the drum and the whole process runs smoothly continuously. Finally paper passes through the fuser which is a heat and presser roller, melts the toner and fixes on the paper perfectly.