Printers

Printers are hardware devices that allow you to create a hard copy of a file. Today a printer is a necessary requirement for any home user and business. Allowing individuals to save their work in the format of paper instead of electronically.

Types of Printers

Impact printers

In case of Impact printer an inked ribbon exists between the print head and paper, the head striking the ribbon prints the character.

Impact printers are basically divided into 2 types :

  • Serial/Character printers
  • Daisy wheel printers

Non Impact Printers

Non Impact printers use techniques other than the mechanical method of head striking the ribbon.

Non Impact Printers are divided into 3 categories :

  • Thermal printers
  • Ink jet printers
  • Laser Printer

Classification of Printers

Quality of type

The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.

Speed

Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.

Impact or Non-impact

Impact printers include all printers that work by striking an ink ribbon. Daisy wheel, dot-matrix, and line printers are impact printers. Non-impact printers include laser printers and ink-jet printers. The important difference between impact and non-impact printers is that impact printers are much noisier.

Graphics

Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.

Fonts

Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document.

Dot Matrix Printers

A dot matrix printer or impact matrix printer refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter.

Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced. Because the printing involves mechanical pressure, these printers can create carbon copies and carbon less copies. The standard of
print obtained is poor. These printers are cheap to run and relatively fast.

The moving portion of the printer is called the print head, and prints one line of text at a time. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.

The print head consists of 9 or 24 pins each can move freely within the tube; more the number of pins better are the quality of output. Dot Matrix Printer Characters are formed from a matrix of dots.

The speed is usually 30 – 550 characters per second (cps). These types of printers can print graphs also. They can only print text and graphics, with limited color performance. Impact printers have one of the lowest printing costs per page.

These machines can be highly durable, but eventually wear out. Ink invades the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires. After about a million characters, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read.

Daisy Wheel Printer

A daisy wheel printer is a type of computer printer that produces high-quality type, and is often referred to as a letter-quality printer (this in contrast to high-quality dot-matrix printers, capable of near-letter-quality,
or NLQ, output). There were also, and still are daisy wheel typewriters, based on the same principle. The DWP is slower the speed range is in 30 to 80 CPS.

The system used a small wheel with each letter printed on it in raised metal or plastic. The printer turns the wheel to line up the proper letter under a single pawl which then strikes the back of the letter and drives it into the paper.

In many respects the daisy wheel is similar to a standard typewriter in the way it forms its letters on the page, differing only in the details of the mechanism (daisy wheel vs type bars or the type ball used on IBMs electric typewriters).

Line Printer

The line printer is a form of high speed impact printer in which a line of type is printed at a time. The wheels spin at high speed and paper and an inked ribbon are stepped (moved) past the print position. As the desired character for each column passes the print position, a hammer strikes the paper and ribbon causing the desired character to be recorded on the continuous paper.

The speed is 300 to 2500 lines per minute (LPM). This technology is still in use in a number of applications. It is usually both faster and less expensive (in total ownership) than laser printers. In printing box labels, medium volume accounting and other large business applications, line printers remain in use.

Line printers, as the name implies, print an entire line of text at a time. Two principle designs existed. In drum printers, a drum carries the entire character set of the printer repeated in each column that is to be printed.

In chain printers (also known as train printers), the character set is arranged multiple times around a chain that travels horizontally pas the print line. In either case, to print a line, precisely timed hammers strike against the back of the paper at the exact moment that the correct character to be printed is passing in front of the paper.

The paper presses forward against a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.

Thermal Printers

Direct thermal printers create an image by selectively heating coated paper when the paper passes over the thermal print head. The coating turns black in the areas where it is heated, creating the image. More recently, two-color direct thermal printers have been produced, which allow printing of both red (or another color) and black by heating to different temperatures.

Thermal Printer Characters are formed by heated elements being placed in contact with special heat sensitive paper forming darkened dots when the elements reach a critical temperature. A fax machine uses a thermal printer. Thermal printer paper tends to darken over time due to exposure to sunlight and heat. The standard of print produced is poor. Thermal printers are widely used in battery powered equipment such as portable calculators.

Laser Printers

A laser printer is a common type of computer printer that produces high quality printing, and is able to produce both text and graphics. The process is very similar to the type of dry process photocopier first produced by Xerox

Laser Printers use a laser beam and dry powdered ink to produce a fine dot matrix pattern. This method of printing can generate about 4 pages of A4 paper per minute. The standard of print is very good and laser printers can also produce very good quality printed graphic images too.

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