In computing, a printer is a peripheral device which converts digital information to permanent marks on paper or other materials. These are most commonly used in conjunction with a desktop or laptop computer, but can in some cases be used with other external devices such as mobile phones or tablet computers. In some cases, printers are built directly into a digital device.
Personal printers are usually small and inexpensive, and most commonly print using the inkjet method. They receive instructions directly from a primary device (computer) through a parallel port (older method) or USB connection. Some also allow wireless connections via Bluetooth or WiFi. They generally operate solely as a peripheral, though sometimes they include fax and/or photocopy functionality.
Network printers are not directly connected to a controller (usually a computer) but rather a print server, which exists as an accessible entity on the local area network. In some cases, the print server is an entirely separate server computer, through which all print jobs are managed. However, sometimes (especially in smaller installations) the printer uses an internal print server. Either way, when something is to be printed, the requesting device connects to the print server through the intranet (or sometimes internet) and spools the print job to it. The print server then has the printer complete the task.
Network printers are commonly used for frequent and high-volume printing, so they often use the Lasterjet method, which is fast and inexpensive. Laserjet printers are at least somewhat larger than most other printers. To provide the speed and functionality required, they are often towers which stand three to four feet tall.
As well as document/photo printers, a common kind of network printer is the label printer. Rather than paper, these use label media to produce marked adhesive labels. In general, label printers use the thermal method of printing, which makes the product inexpensive and keeps the printer cleaner. However, these labels are susceptible to heat, so some variations are also sometimes used.
These labels are most commonly used in warehouses and other support facilities. These usually depict predominantly a barcode, so the item they are attached to may be easily scanned. Other relevant information is usually included as well, and the labels sometimes also are created with an embedded RFID chip.
For a more detailed treatment, see Plotter printer.
Plotter printers are used to produce images, usually on large sheets of paper. As plotter technology evolves, theses printers become faster, but they still generally take some time to complete their tasks. Since they are slower than most other modern printers, they are generally not used for regular-sized printing tasks.
For a more detailed treatment, see Three-dimensional printer.
3D printers are a new technology that enables users to print a solid object using a variety of materials. Just as an ink jet printer can be used to deposit ink or a marking substance on a flat piece of paper, similar mechanisms can be used to deposit a bulky substance instead. As such substances cure, they can accumulate to form a three dimensional object. As the printer makes repeated passes over the object the pattern of depositing the substance can change, which will affect the ultimate shape of the object. To use this type of printer a user creates a 3D model on a computer, then sends the job to the printer. The printer then constructs the object on a mat, by moving the nozzle (or print head) on a dual-axis assembly and releasing small amounts of the material where it is needed. In general, these printers are very slow in comparison to 2D printers, but the technology is still evolving and improving significantly. These are used in private, educational, manufacturing, medical, and other venues.
Virtual printers have earned their name quite simply because they are not really printers at all. These printers have no physical module, but are rather computer programs. The operating system and other software recognizes these as printers, but when something is "printed" to one, the task is spooled into a file, rather than an actual printer. Perhaps the most common virtual printer is produced by Adobe, which "prints" to PDF.
Throughout the evolution of printing technology, many methods of printer have been invented. The following are some of the more presently or formerly popular varieties.
Inkjet printers are popular, since they offer several advantages. These include high-quality printing, inexpensive printer devices, and quiet operation. However, inkjet printers use proprietary ink cartridges, which are usually expensive, and this ink tends to fade over time, so the product does not last as well as it might if printed differently. They operate by ejecting small drops of ink onto the paper as needed. This process (called drop-on-demand) can be performed several different ways.
The most common method of inkjet printing uses the bubblejet technique. Resistors in the print head are used to produce heat which vaporizes some of the ink, creating a bubble. This bubble of gas propels a droplet of liquid ink out of the head and onto the medium.
Piezoelectric printers use, as the name implies, piezoelectric crystals to generate the required ink jets. Small quantities of one or more of these selected materials are placed in the print head. When power is applied to the material, it changes shape, pushing a small droplet of ink out onto the medium.
Care and maintenance
The main problem these printers experience is clogging of the print heads. They can usually be cleaned fairly easily using isopropyl alcohol. However, the printer must be opened up and the print heads removed to do this, and once done, the printer usually must print one or more alignment sheets (which consumes expensive ink). Many Inkjet printers have the print heads on the actual ink cartridges, which means that each time the cartage is replaced, so is the head.
The laser printing method uses a laser to "paint" the desired image onto a photosensitive imaging drum. Toner is then picked up by the drum, and transferred to the paper. Heat an pressure are then applied to the paper to fuse the plastic-based toner to the sheet. Black printer one go through this process once, but color printer must do so four times. There are four photoreceptive drums, one is used for each color—yellow, magenta, cyan, and black. Each drum prints its color onto a belt, then a transfer roller moves the toner to the paper. The printing process is as follows:
- Processing: Construct the page in memory
- Charging: Put an negative electrostatic charge on the imaging drum
- Exposing: Write the image on the drum using laser
- Developing: Add negatively charged toner to the drum (it will be repelled by all areas except those written on by laser)
- Transferring: Place the toner from the drum onto the paper (If printing color, transfer to a belt first, then the paper)
- Fusing: Apply heat and/or pressure to the page
- Cleaning: Remove excess toner
Care and maintenance
Since these printer use powder toner, they tend to get quite dirty over time, and should be cleaned periodically. However, compressed air should not be used in most cases, since the toner may become lodged in more vital areas, and this will generally make a mess of the surrounding area. Cold water on a cloth is usually the best option for cleaning most surfaces, and isopropyl alcohol cleans the rollers well.
Dot Matrix printers are a kind of impact printer, which are not used nearly as much as they once were. However, they still have their uses since printing is inexpensive and they can produce multiple copies using thermal transfer or carbon paper. Unfortunately, these printers are very noisy, offer poor print quality, and use proprietary ink cartridges. Rather than having set dies for each letter, as some early impact printers did, a dot matrix printer uses pins to form the desired shapes. When printing:
- The top edge of a continuous sheet of pin fed paper is aligned just above the print head
- The print head moves from side to side, rapidly extending and retracting pins where marks should appear on the paper.
- A ribbon runs between the paper and the print head, so the pins press this ribbon against the paper, leaving ink behind
- The ribbon loop continuously feeds from the ink cartage to the head and back again to maintain the availability of ink.
- When the print job is complete, extra paper is fed out, so that the product may be torn or cut off
Thermal printers do not use any ink or toner. Rather, they use direct-thermal paper, which turns black in response to heat. These printers are limited to black printing only, and the final product can be destroyed sunlight, hot surfaces, or friction. However, they are inexpensive and convenient for a number of purposes, including shopping receipt printing and label production.
The most common form of thermal paper contains bisphenol A, which raises health concerns because the substance transfers to the skin of the person holding the paper. BPA is then absorbed by the skin to varying degrees. Some thermal media also contains bisphenol S, which although believed to be slightly less harmful than BPA, is absorbed more easily thus increasing the exposure quantity.
Care and maintenance
Since no ink is used, thermal printers tend to stay fairly clean. However, paper fragments and dust can still build up, so these should be cleaned from time to time. Compressed air and/or a damp cloth can be used to clean it manually. Some printers can also be cleaned by feeding through a cleaning card.
- Sandra Biedermann, Patrik Tschudin, & Koni Grob, "Transfer of bisphenol A from thermal printer paper to the skin", Analytical and Bioanalytical Chemistry, September 2010, Volume 398, Issue 1, pp 571–576