Printers : Daisy Wheel, Dot Matrix, Inkjet Printers & Laser Printers

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.

Fig. 1: A Figure Showing Printer as an Electromechanical Device Converting Text into Graphical Content

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.

Fig. 2: An Image Showing Working of Daisy Wheel Printers for Printing Characters and Symbols

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.

Fig. 3: An Image Representing Daisy Wheel, a Circular Printing Element Allowing Printing Hammer to Print Characters Against Paper

Dot Matrix Printers

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 printhead 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).

Fig. 4: An Image Representing Dot Matrix Printers Printing Text and Graphics Using Tiny Dots in the Desired Shape

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.

Fig. 5 : A Figure Illustrating Printheads Driven by Several Print Hammers Through Solenoids to Print Text

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.

Inkjet Printers

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

Fig. 6: A Representational Image of Inkjet Printers to Produce Full Colored Hard Copies

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:

· 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).

Fig. 7: A Figure Showing Monochrome and Colored Print Cartridge Contained in Inkjet Printer

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.

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.

Laser Printers

4. Laser Printers

Fig. 8: A Representational Image of Laser Printers Used for Large-Scale Quality Printing

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’. Componetns of a laser printer is shown in the following image:

Fig. 9: A Figure Depicting Different Components of Laser Printer

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 photoconducting 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 tonner on the paper. It is coated with charged tonner particles. As the drum touches the developer roller, the charged tonner 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.

Monochrome v/s Color

Monochrome v/s Color Printers

Color printers work on the same concept of monochrome printers. They use four color toners (ink cartridges in case of inkjet printers) instead of one black colored toner in the black and white printers. Typically the colors are –Cyan, Magenta, Yellow and Black that are used to print in full color. There are four different drums and each drum is associated with the separate color toner. When printer receives the printing data, the paper is charged corresponding to the different color drums. The paper passes through each drum and the corresponding color toner particles gets stuck on the paper. As the paper passes through all four drums, the desired colored shape gets printed on the paper. Since the paper passes through four drums, color printers are four times slower than the monochrome printers and several times expensive.

The below video shows how exactly a color laser printer works:

Special Printers

5. Some special types of printers

Despite these printers there are also some function specific printers these are designed for special purposes.

Photo Printer – These inkjet printers are color printers that produce photo lab quality pictures on photo papers. Although they can also be used to print documents but they are specially designed for printing the photo. They have a large number of nozzles that can print very fine droplets to enhance the image quality. They can print a 4 x 6 inch photos directly from the digital cameras without need of a computer.

Fig. 10: A Representational Image of Photo Inkjet Printers Producing Photo Lab Quality Pictures on Photo Papers

Dye Sublimation Printers – These are latest innovative printers that are specially designed for high quality photo printing. They magnetize the ink over a charged paper to produce a very high quality picture. These printers are suitable to photo hobbyists but are a quite expensive.

Fig. 11: A Representational Image of Dye Sublimation Printers Designed Especially for High-Quality Printing

Portable Printers – They are small light weight inkjet or thermal printers specially designed for the users to carry out with the laptops while travelling. Generally these printers have a lower quality for image printing and higher cost because of its compact design.

Fig. 12: A Representational Image of Portable Thermal or Inkjet Printers Ideal to Carry with Laptop

Multifunction Printers – Also known as all in one printers are the combination of various functionalities like printer, scanner, photo copier, fax, etc.

Fig. 13: A Representational Image of Multifunction Printer Equipped with Scanner, Fax, Photo Copier, Printer, and etc.

History

History of Printers

The history of printers dates back to 1938, when a patent attorney and a graduate of Caltech, Chester Carlson developed a dry printing process called electrophotography. Later in 1949 Haloid company of New York agreed to use this process to develop dry copying process which was then called xerography. Eventually the Haloid Company changed its name as Xerox Corporation.

UNIVAC, Universal Automatic Computer was one of the earliest computers. UNIPRINTER was the printer built to work with the UNIVAC with a speed of 600 lines per minute. With the continuing research over the xerography, in 1971, Gary Starkweather, a Xerox engineer build a laser printer and named it as “SLOT” (Scanned Laser Output Terminal). In the next year, a digital control system and character generator was developed for the laser printer by Butler Lampson and Ronald Rider. These all combined efforts resulted in a printer named ‘EARS’ (Ethernet, Alto, Research character generator, Scanned laser output terminal). This printer subsequently became available commercially as Xerox 9700 laser printing system in 1978.

In the 1976, IBM introduced the first inkjet printer which set the new standards for print quality. After two year Canon launched their printer with the “Bubble Jet” concept. In 1984 Hewlett Packard introduced ThinkJet which used a disposal printhead with 12 individually controlled chambers that ejected the drops of ink from the nozzle. This printer works with a speed of 150 characters per second and a resolution of 96 dpi. In 1983, Canon also introduced the LPB-CX laser printer with a disposable cartridge and a resolution of 300×300 dpi. Hewlett-Packard released the popular LaserJet 4 having a resolution of 600 x 600 dpi in 1992.