In this article, impact and non-impact printers are explored, with descriptions of each major printer type. The methods printers use to move paper are explained. The maintenance techniques for cleaning and calibrating printers are described. Laser printer operation is described in some detail.
Lesson Objectives
- Identify printer features.
- Identify the advantages and disadvantages of specific printer types.
Printers
Printers are still important when a physical paper-based document is required. With the advent of digital signatures and the ease of transmission of electronic documents, the role of the printer is becoming less critical for day-to-day work.
On the other hand, the use of 3D printers is growing rapidly, with applications in aeronautics, medicine, and manufacturing.
Types of Printers
For our purposes, a printer is a device that produces a paper copy of information generated by a computer. Figure 1 shows various traditional printers.
Figure 1. Traditional Printers
Printers can be categorized functionally according to whether or not the printing mechanism involves physically touching the paper while printing:
- Impact printers use a device to strike an ink tape or ink ribbon so as to press the ink onto the paper. Impact printers include dot matrix printers and printers with interchangeable print heads.
- Non-impact printers use a method to place ink or another substance on the paper without physically touching it. Non-impact printers include inkjet printers, laser printers, snapshot printers, plotters, wide-format printers, and thermal printers.
Impact Printers Types
Impact printers actually impact inked tape or inked ribbon, which in turn impacts the paper. This has the effect of forming characters on the paper. Printers that require carbon paper or No Carbon Required (NCR) paper are special types of impact printers.
Dot matrix printers are legacy impact printers that draw letters on paper by imparting arrays of dots using a print head and inked ribbon. A dot-matrix print head contains rows of small blunt pins that stamp an image on the page.
Pin configurations are commonly comprised of 9, 18, or 24 pins, as illustrated in Figure 2. A greater number of pins results in a smoother representation of characters on paper.
Figure 2. Dot Matrix Print Head Pin Configurations
Dot matrix printers are susceptible to print head failures, requiring the print head to be replaced. The print head requires manual alignment to keep the characters standardized. Dot matrix printers can print multiple copies of a document. One drawback of dot matrix printers is that they cannot print graphics.
The other type of impact printer uses interchangeable ball-shaped or wheel-shaped print heads, as illustrated in Figure 3.
Figure 3. Impact Printer with Wheel-Shaped Print Head
These printers provide better quality than dot matrix printers but are generally more expensive. Like dot matrix printers, they can print multiple copies of a document. As the print head moves across a piece of paper, a small hammer impacts the print head, ribbon, and paper, forming a character. Figure 4 illustrates how much better a character formed by a print head appears compared to a dot matrix. The advantage of a dot matrix printer is its speed.
Figure 4. Print Head and Dot Matrix Produced Character
It is very difficult to change fonts and font sizes with these printers – if a different font is needed, one must replace the entire wheel or ball. These printers are functionally very similar to electronic typewriters. Like dot matrix printers, these printers cannot print graphics.
Impact printers have two common methods of moving paper through the printer:
- Friction feed uses friction to hold the paper against the platen, which is the big roller in the print path that the printer head strikes. The paper advances through the printer as the plate turns.
- Pin feed or tractor feed pulls the paper through the printer by a set of pins that fit into the perforated holes along the edge of the form. These pins may be integrated into the platen or mounted on a separate, motor-driven tractor.
Watch the video Understanding Impact Printers (3:13) to gain a better understanding of impact printers.
Non-Impact Printers Types
Non-impact printers are purchased and used much more frequently than impact printers. Inkjet printers and laser printers are the most common types of non-impact printers; inkjet printers rely on ink transfer, and laser printers rely on toner transfer. The other major categories of non-impact printers are snapshot printers, plotters, wide-format printers, and thermal printers.
Inkjet Printers
Inkjet printers spray liquid ink particles from cartridges through tiny holes called nozzles. Figure 5 illustrates cyan, magenta, yellow, and black inkjet ink cartridges.
Inkjet printers usually print one line at a time. Inkjet printers are faster than dot matrix printers but slower than laser printers. Inkjet printers are also smaller and less expensive than laser printers. Inkjet printers provide an economical means of printing color documents.
The quality of the paper has a significant influence on the quality of printed output; for example, using inexpensive paper with an inkjet printer increases the tendency for smudged output.
Figure 5. Inkjet Toner Cartridges
Inkjet printers form drops in one of two methods:
- Thermal shock-heats the ink in a capillary tube just behind the nozzle. This increases the pressure of the ink in the reservoir and causes it to explode through the opening.
- Mechanical vibration uses vibrations from a piezoelectric crystal to force ink through a nozzle.
Color inkjet printers spray tiny droplets of ink through nozzles, one nozzle per color, as illustrated in Figure 6. Black and three or four other colors are used to additively create all possible colors.
Figure 6. Inkjet Printer Operation
The quality of inkjet printing has improved dramatically over the years. Moore’s law applies well to inkjet printing technology – these printers have become so inexpensive that one could argue that they are practically disposable. But while the printer itself is inexpensive, ink cartridges are not cheap.
Watch the video Understanding Ink Jet Printers (5:00) to gain a better understanding of inkjet printers.
Laser Printers
Laser printers rely on static electricity to transfer toner, a mixture of polymer and plastic particles, to paper. Laser printers are generally preferred because they print at high resolutions, they are reliable, and they are fast. Figure 7 shows a typical laser printer.
Figure 7. Laser Printer
Dots per inch (DPI) is often used as a measure to describe the quality of printed output. Table 1 compares print quality and speed for dot matrix, inkjet, and laser printers.
Table 1. Dot Matrix, Inkjet, and Laser Printers
* The number of pins in the print head configuration, such as 9, 18, 24, or 48, determines the print quality.
As with photocopiers, static electricity is the primary operational mechanism for laser printers. This is the same physical phenomenon that creates lightning. The attraction of opposite charges and the repulsion of like charges make it possible for a laser printer to temporarily hold toner to a statically charged image on a positively charged photoconductive drum. A laser beam is then used to draw the image.
Laser printers are excellent when high-volume printing is required. Laser printers have been used in business for decades, but lower prices have also made them common for home use.
Laser Printer Operation
There are six steps to laser printer operation:
- cleaning
- conditioning
- writing
- developing
- transferring
- fusing
The six steps are illustrated in Figure 8. The first four steps take place inside the toner cartridge on most printers.
Figure 8. Laser Printer Operation
- During the cleaning phase, the old unused toner is removed from the drum. A blade, similar to a windshield wiper, scrapes the excess toner from the drum. The excess toner is stored in a used toner container that is either housed inside the toner cartridge or in a separate container that can be emptied or discarded. See Figure 9.
Figure 9. Laser Printer Cleaning Phase
- During the conditioning phase, residual images are removed from the printer drum.
- During the writing phase, the laser applies an invisible image onto the photosensitive drum via electrostatic charge.
- During the developing phase, the toner is applied to the invisible image on the drum via electrostatic attraction.
- During the transferring phase, the transfer places a positive charge on the paper, and then the negatively charged toner is attached to the positively charged paper.
- The final step is fusing. As the paper passes between a 350-degree Fahrenheit roller and a pressure roller, the plastic particles in the toner are melted and fused into the paper. After the fusing operation is complete, the paper is moved to the output tray, as a printed page.
Watch the video Understanding Laser Printers (9:47) to gain a better understanding of laser printers.
Snapshot Printers
A snapshot printer is a small format printer used to print digital photographs. They are generally slower than other printers and more expensive to operate, but they can produce high-quality images. They have interfaces that allow you to directly plug a camera or media cards into the printer.
Plotters and Wide-Format Printers
Plotters, or pen plotters, print line drawings, or more generally, vector graphics. Plotters use automated pens of assorted colors to draw high resolution point-to-point continuous lines to form multicolor line drawings. These line drawings comprise technical drawings on paper up to six feet wide.
Plotters were once used extensively by engineers and architects for computer-aided design (CAD). Figure 10 shows a typical plotter. The term wide-format printer is normally used nowadays in place of the term plotter in the context of modern CAD applications because inkjet and laser printing technologies have replaced pen-based printing technologies.
Figure 10. Plotter
Wide-format printers, or large-format printers, are simply printers that can accommodate printing onto materials between eighteen and one hundred inches wide. Early wide-format printers applied a substrate directly onto a material as an array of dots.
Newer wide-format printers use inkjet or laser jet printing technologies. Wide-format printers are frequently used in marketing and advertising to print signs, banners, and posters.
Thermal Printers
Thermal printers use special paper and a heating element to burn images into the paper. Thermal printers are commonly used for printing receipts and as CD/DVD/Blu-ray disc label makers, as shown in Figure 11.
Figure 11. Thermal Printers
Watch the video Understanding Thermal Printers (2:13) to gain a better understanding of thermal printers.
Printer Selection Criteria
When selecting a printer for purchase, take the following characteristics, expressed in bold font, into consideration:
- Resolution is the density of the printed dots that comprise an image. Printers support different resolutions.
- Speed describes how quickly a page is printed.
- Consumables significantly impact the overall cost of a printer. Ribbons and inkjet cartridges are cheap compared to laser printer toner. But ribbons and inkjet cartridges tend to dry out faster and produce fewer copies. In fact, comparing price per page, laser printers turn out to be much cheaper to operate.
- Check the size and type of paper the printer accepts. If it is necessary to print on envelopes or labels or special media, make sure the printer supports that feature. Paper is specified in terms of its weight per 500 sheets at 11″ x 17″. Store paper in a cool/dry place.
- Color printers require more cartridges and can be expensive to operate. Color printers usually use cyan, magenta, yellow, and black ink or toner to create color images on a page. Color inkjet printers are the most popular because they are less expensive per cartridge, but they are more expensive per page.
- As a general rule, the length of a printer warranty ranges from ninety days to one year. Consider purchasing an extended warranty or service contract for a printer.
Summary
- Printers are categorized into impact and non-impact printers.
- Impact printers rely on striking a tape or ribbon to physically impart characters on a page; dot matrix printers are the most common type of impact printer.
- Non-impact printers include inkjet, laser, snapshot, wide-format, and thermal printers.
- Inkjet printers spray liquid ink onto paper and laser printers work by fusing toner to paper; inkjet printers are cheaper than laser printers, but laser printers are cheaper per page of printing.
- The six steps of laser printer operation are cleaning, conditioning, writing, developing, transferring, and fusing.
- Select a printer based on resolution, speed, consumables, print media, color, and warranty.
