Theory-10 :- Types Of Printers

A printer is any device that prints text or illustrations on paper. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories:

1. daisy‐wheel: Similar to a ball‐head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy‐wheel printers produce letter‐quality print but cannot print graphics.

2. dot‐matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.

3. ink‐jet: Sprays ink at a sheet of paper. Ink‐jet printers produce high‐quality text and graphics.

4. laser: Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.

5. LCD & LED :Similar to a laser printer, but uses liquid crystals or light‐emitting diodes rather than a laser to produce an image on the drum.

6. line printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low‐quality print.

7. thermal printer: An inexpensive printer that works by pushing heated pins against heat‐sensitive paper. Thermal printers are widely used in calculators and fax machines.

What is a Printer? A printer is an electromechanical 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 wirelessly 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.

Types of Printers Since the invention of the printing technology, a variety of technologies have been employed in computer printers. Broadly printers are categorized as impact and non impact printers. Impact printers are the type of printers in which a key strikes the paper to make a letter. The examples of Impact printers are Daisy wheel and Dot matrix printers. While non‐impact printers do not operate by striking a head against a ribbon. Inkjet printers and laser printers are the non‐impact printers. The most popular printers are described.

1.     Daisy Wheel Printers Daisy wheel printers print only characters and symbols and cannot print graphics. They are generally slow with a printing speed of about 10 to 75 characters per second. By 1980 daisy wheel printers were the dominant printers for quality printing but since the prices of laser and inkjet printers have declined and quality of dot matrix printers has been improved, the daisy wheel printers are now obsolete.

Working of daisy wheel printers is very similar to typewriters. A circular printing element (known as daisy wheel, shown in the below image) is the heart of these printers that contains all text, numeric characters and symbols mould on each petal on the circumference of the circle. The printing element rotates rapidly with the help of a servo motor and pauses to allow the printing hammer to strike the character against the paper.

 2. 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).

3. Inkjet printers Inkjet printers are most popular printers for home and small scale offices as they have a reasonable cost and a good quality of 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: ∙         

Print head – 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 printer head and ink cartridges back and forth across the paper. .       

Stabilizer bar – A stabilizer bar is used in printer to ensure the movement of print head is précised and controlled over the paper. .     

Belt – A belt is used to attach the print head 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 ‘print head’ as a key element. The print head has many tiny nozzles also called as jets. When the printer receives the command to print something, the print head starts spraying ink 33 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.   

An inkjet printer can print 100 to several hundred papers depending on the nature of the hard copy before the ink cartridge need to be replaced.

4. Laser Printers 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 are 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.