Before you start
Objectives: learn how do dot matrix, ink jet, solid ink, dye sublimation and laser printers work, and which type of interface can they use.
Prerequisites: no prerequisites
Key terms: ink, paper, print, dot, matrix, jet, head, solid, laser, pins, dye, quality, ribbon, usb, parallel
Dot Matrix Printer
A dot matrix printer is an impact printer that transfers characters by striking a pattern (from a matrix) through an inked ribbon and onto paper. There are four critical components in a dot matrix printer. The first is the print head which is a square block, and it’s got a series of pins. The second important component is called the platen. Platen is the black roller that we put paper through and roll it around. It’s like a big cylinder and its job is to hold the paper in place and serve as a backing to which the print head can hit. Other components are ribbon and the tractor feed. The ribbon contains the ink that will be transfered onto the paper, and the tractor feed is used to draw continuous-feed paper up through the printer. The tractor feed pulls a piece of paper and rolls it around the platen.
335.1 – Dot Matrix
The number of pins in print head can vary. Inexpensive dot matrix printer will only have nine pins, as in our case. Higher quality dot matrix printer might have upwards of 24 different pins. The most common number of pins on a dot matrix printer is 9, 18, or 24, with more pins providing a higher resolution. 24-pins create a near-letter quality print and anything with less than 24-pins provides a draft quality print. Each of these pins is actually retracted inside the print head and they’ve got springs that keeps them pulled inside of the print head. In the back they also have an electrical solenoid. To print, the printer sends electrical current through the pattern of those pins. When the solenoid receives that current, it fires the pin out of the print head. The pin then smacks the ribbon and then paper which leaves an imprint on the paper. By using a different variety of patterns, we can create different letters. A lot of the nine-pin dot matrix printers provide an option where it makes two passes for each line of text. By doing that, it can actually create better looking letters. The down side of that is that it takes twice as long to print. The speed of dot matrix printers is measured in characters per second (CPS). Common speeds for a dot matrix printer are 32 to 72 CPS.
Dot matrix printers are still used today, and the reason is that dot matrix printers can can print in duplicate or triplicate using forms. That means we can put carbon copies through the dot matrix printer and have them print out. The overall print quality of a dot matrix printer is quite poor when compared to that of other types of printers. They can also be pretty loud because printing takes place by pins physically striking the ink ribbon, paper, and the platen.
Ink Jet Printer
Ink jet printers can create high quality output and they are cheap. Just like with the dot matrix printer, we have our platen and we use a form-feeder to pull a piece of paper through, wrap it around the platen, and insert it between the platen and the print head. Unlike a dot matrix printer, which uses continuous-feed paper, an ink dispersion printer actually uses cut sheets of paper, just like we would use for a copy machine. The print head in an ink dispersion printer is similar to a dot matrix printer in some way. However, instead of having pins inside that come out and strike the ribbon, we have a bunch of nozzles which contain ink. When printing, the current is applied to a specific pattern of nozzles. The ink that’s inside of the nozzle then boils, which creates an air bubble. When that happens, it actually shoots a jet of ink and makes a dot on the piece of paper. By varying the current and applying it to different nozzles in the print head, we’re able to create different patterns on the paper. This kind of Ink Jet printer is called a Bubble jet printer, and it is the most popular form of ink jet printer.
The crispness of an ink jet printer’s image is usually rated in terms of Dots Per Inch or DPI. Ink jets range from 150 to over 1400 DPI. New ink jet printers can produce photo-quality printouts when used with photo-quality paper. They do have one weakness and that is the fact that most of the electronic circuitry that makes up the printer is not actually in the printer, itself. Most of the electronic circuitry that makes up the ink jet printer is actually in the print head. So when we have to change the ink reservoir, we actually have to buy new printer component. That’s why the cartridges are so expensive, and the printer itself is so cheap.
Solid Ink Printer
A solid ink printer creates smaller, more uniform dots than a dot matrix or ink jet printer. Instead of using a ribbon or liquid ink, a solid ink printer uses solid sticks of ink. The process for printing in a solid ink printer is a little bit different than in a dot matrix or inkjet printer. It’s kind of a hybrid between an ink jet printer and a laser printer. In a solid ink printer, solid ink sticks are inside of the print head. The melted ink is then jetted onto a drum which is as wide as the paper, and which rotates. A piece of paper is then drawn from a paper tray and is rotated around the drum. The melted ink from the drum is then transferred onto the piece of paper. The ink then cools and adheres itself to the paper.
Thermal printers use an older, thermal technology. Many of the older fax machines use thermal technology. Instead of using ribbon, ink or melted ink sticks, we use special paper that reacts to heat. We use heat to transfer an image from the printer to the special paper. That special paper is pretty expensive and it is also looks a bit different when it comes out of the printer. It has a glossy feel to it. Monochrome thermal paper is chemically treated to darken where heated (photosensitive). Many cash registers use this type of printer for creating receipts. Color thermal paper is chemically treated to absorb color from a ribbon where heated. Ink is applied via the ribbon in a similar manner to a solid ink printer. The color system used by thermal printers is CMYK (Cyan, Magenta, Yellow, and black). The paper must make one pass for each application of a different color. Color thermal printers are very expensive, high quality, and operate quietly.
Dye Sublimation Printer
A dye sublimation printer allows us to print high quality pictures. They provide a smooth blending of colors. That’s something that’s hard to achieve with other types of printers. It’s also less vulnerable to fading and distortion over time. In dye sublimation printing, the colors are not laid down as individual dots, as with an ink jet, solid ink, or dot matrix printer. Instead, inside of a dye sublimation printer we have a long roll of semi-transparent film. That film is made up of individual red, blue, yellow and gray sheets of film. In this film solid dyes are embedded, corresponding to the four basic colors used in high end printing, which are cyan, magenta, yellow and black. In this kind of printer we also have a print head, like we do with other types of printers. Then we have our transparent film, and then we have our piece of paper.
335.2 – Dye Sublimation
The print head heats up and passes over the transparent film. As that happens, the dyes that are within the film vaporize and are transferred to the paper. The dye actually permeate the glossy surface of the paper. As they cool they return back to the solid form. In this way we can transfer a very high quality image to the piece of paper. Dye sublimation printers create a gentle gradation. Instead of having distinct dots of particular colors, dye sublimation printing prints in transitioning colors rather than pixels.
Laser printers produce very high quality output for a relatively low price. Other types of printers such as a dot matrix or an ink jet printer print data one line at a time. With laser printers we use a laser beam to transfer an image to a photo sensitive drum. The laser creates a mirror image of the document we want to print on the drum. This charges the drum, and because of that we can transfer toner (which is fine plastic) onto the surface of the drum, run a piece of paper underneath it, transfer the toner to the paper and then run the paper between fuser to actually melt the toner into place.
335.3 – Laser Printer
Instead of printing one line at a time, laser printers actually print one page of data at a time. One page of data is transferred to the drum and one piece of paper at a time rolls through and has the image transferred onto it. Laser printers have to have lots of memory because instead of just remembering one line at a time of data they have to remember an entire page. Text does not use up much memory, but complex graphic can use up very much memory. Modern laser printers don’t have this problem, they have enough memory to handle very complex graphics. Of all the types of printers discussed in this article, laser printers have the highest print quality.
Over the years, a variety of different types of interfaces have been implemented that allow us to connect our PC system to the printer. Some of them are no longer used. The oldest one is the serial interface.
In the early days of printing, we sent documents to the printers using a serial connection. This worked, but serial connections had a couple of disadvantages. Number one, they were hard to configure. We had to configure the start bits, stop bits, flow control, transmission rate, and parity. In addition, it was slow because the document is sent to the printer one bit at a time. One of the great advantages of serial interface was the fact that the printer cable itself could be very long.
For a time, there were a variety of different SCSI interfaces used to connect work stations to printers. SCSI stands for Small Computer System Interface. They weren’t used that often because SCSI printers were also hard to configure. We had to understand the concept of termination and ID. However, they were used for high-end printers where performance was an issue.
Parallel printers used to be the standard method of connecting printers to a computer. Parallel was a lot easier to implement than serial or SCSI. With the parallel printer, we plugged one end into our work station, the other end into the parallel port on our printer, and that was it. Also, it was faster than serial connection. Parallel interface is being replaced by USB.
USB is also easy to use. There is no configuration needed. We just plug everything in and it works. With USB we can connect multiple printers to our computers, because we usually have multiple USB ports on our computer. With parallel we couldn’t do that since we usually had one parallel port.USB connections increase speed considerably when comparing to a standard serial port.
In addition to USB, another standard that’s used to connect printers is FireWire. FireWire has not caught on as strongly for printing as USB, but they have a lot of the same advantages as USB.
We can also use an infrared interface to connect our work station to the printer. Instead of using a wire, we use an infrared light signal to send information from our work station here to the printer. Infrared connections are actually serial connections using light and air instead of wires to make the connection. Infrared has some limitations like line of sight (no obstructions in the path). In addition, if the printer is too far away, more than about a meter away, then things start to go wrong. There are also security issues. The infrared signal can be picked up by anybody else with an IR port.
In addition to IR we can also use a wireless connection (802.11a/b/g/n standards) to send print jobs from a work station to a printer. Wireless uses a radio signal to send the print job to the printer. With wireless we’re not concerned with obstacles. The radio waves can go through things. We can move the printer into a different room and still be able to print our documents. In addition, with radio signals, we can configure encryption so that we don’t have to worry about somebody intercepting radio signals.
Some printers also have their own network interface card. In that case we connect our printer to the network on which our workstation also resides. In that way we can send our print job through the network medium to the printer. Network printers are useful for allowing multiple people to share the same printer.
A dot matrix printer is an impact printer. Ink jet printers are non-impact printers with ink stored in a reservoir. Laser printers use lasers and electrical charges to transfer images to paper. A dye sublimation printer is a non-impact printer that uses film-embedded dye. Solid ink printers melt ink onto the print head, which is as wide as the paper. A thermal printer is a non-impact printer that uses heat to cause a reaction on specially treated paper. Today printers use either a parallel, USB, wireless or a network connection.