Chapter 27 Printers and Multifunction Devices (220-901)

ASCII

ASCII contains a variety of control codes for transferring data, some of which can be used to control printers. For example, ASCII code 10 (or 0A in hex) means "Line Feed" and ASCII code 12 (0C) means "Form Feed". These commands have been the standard since before the creation of IBM computers, and all printers respond to them.

PostScript

Adobe Systems developed the PostScript page description language in the early 1980s as a device-independent printer capable of high resolution graphics and scalable fonts. PostScript printers print a lot faster. PostScript files are very portable.

Printer and Multifunction Device Components and Technologies

Many printers nowadays can be an all-in-one, which means that they can contain a printer, scanner, copier, and a fax machine all in one machine.

Printer Languages

Printers have different languages and ways of how they communicate with the computer.

Print to XPS

Windows versions since Vista include the Microsoft XPS Document Writer as a printer, which you can use to create a .xps file that can be opened by the included XPS Viewer program.

Hewlett-Packard Printer Control Language (PCL)

HP developed PCL as a more advanced printer language to supersede simple ASCII codes. PCL features a set of printer commands greatly expanded from ASCII. HP designed PCL with a text-based output in mind; it does not support advanced graphical functions. The most recent version of PCL, PCL6, features scalable fonts and additional line drawing commands. PCL is less portable than PostScript because the commands must be supported by each individual printer model.

Print to PDF

One of the most popular virtual printing options is the ability to print to PDF, a feature many operating systems support out of the box these days. On older versions of Windows you needed to install a virtual printer to get the Print to PDF option. It is on Windows 10 by default however.

Primary Corona/Charge Roller

The primary corona wire , located close to the photosensitive drum, never touches the drum. When the primary corona or primary charge roller is charged with an extremely high voltage, enabling voltage to pass to the drum and charge the photosensitive particles on its surface. The primary grid regulates the transfer of voltage, ensuring that the surface of the drum receives a uniform negative voltage of between 600 and 1000 voltage.

Laser

The laser acts as the writing mechanism of the printer. Any particle on the drum stuck by the laser becomes conductive and its charge is drained away into the grounded core of the drum.

Turning Gears

A laser printer has many mechanical functions. First, the paper must be grabbed by the pickup roller and passed over the separation pad, which uses friction to separate a single sheet from any others that were picked up. Next, the photosensitive roller must be turned and the laser, or a mirror, must be moved back and forth. The toner must be eventually distributed, and the fuser assembly must squish the toner into the paper. Finally, the paper must be kicked out of the printer and the assembly must be cleaned to prepare for the next page. More sophisticated laser printers enable duplex printing, meaning they can print on both sides of the paper. This is another mechanical function with a dedicated duplexing assembly for reversing the paper. All of these functions are served by complex gear systems. In most laser printers, these gear systems are packed together in discrete units generically called gear packs or gearboxes. Most laser printers have two or three gearboxes that you can remove easily if one happens to fail.

Virtual Printers

A virtual printer is pretty similar to physical or "real" printing. When you print to a virtual printer, your system goes through all the steps to prepare a document for printing, and sends it off to a virtual printer, a program which converts the output from your computer into a specific format and saves the result to a portable file that looks like the printed page would have. You can print this file later if you like, or maybe send it to someone else to print, but you can also just keep it in digital format. Virtual printers provide a nice way to save anything you can print, and they're particularly good for saving reference copies of information found on the web. Simple terms: A virtual printer is not really a printer at all; it is a piece of software installed on your computer. Its user interface is similar to a printer driver, but the virtual printer is not connected to an actual printer.

Power Supplies

All of the devices described in this chapter have power supplies, but when dealing with laser printers, techs should take extra caution. The corona in a laser printer requires extremely high voltage from the power supply, making a laser printer power supply on of the most dangerous devices in computing. Turn off the printer and use caution before servicing.

Inkjet Printers

An inkjet printer uses a printhead connected to a carriage that contains the ink. A belt and motor move the carriage back and forth so the ink can cover the whole page. A roller grabs paper from a paper tray (usually under or inside the printer) or feeder (usually on the back of the printer) and advances it through the printer. The ink is stored in special small containers called ink cartridges. Older ink jet printers had two cartridges: one for black ink and another for colored ink. The color cartridge had separate compartments for cyan (blue), magenta (red), and yellow ink, to print colors by using a method known as CMYK. If your color cartridge ran out of one of the colors, you had to purchase a whole new color cartridge or deal with a messy refill kit. Printer manufacturers began to separate the ink colors into three separate cartridges so that printers came with four cartridges: one for each color and fourth for black. This costs a bit of money but it produces the best quality printouts for the user. Today you can find color inkjet printers with six, eight, or more color cartridges. Printers that use more cartridges have a higher quality printout, but they cost a lot more money. The two key features of an inkjet printer are the print resolution, how densely the printer lays down ink on the page, and the print speed. Resolution is measured in dots per inch (dpi); higher numbers mean that the ink dots on the page are closer together, so your printed documents will look better. Print speed is measured in pages per minute (ppm).

System Board

Every laser printer contains at least one electric board. On this board is the main processor, the printer's ROM, and the RAM used to store the image before it is printed. Many printers divide these functions among two or three boards dispersed around the printer. On older printer models you can upgrade the ROM chips on the system boards. This is to fix the firmware if there are any bugs or other issues. When the printer does not have enough RAM to store the image before it prints, you get a memory overflow problem. Adding RAM is a simple job, just snapping in the RAM stick like you would with a laptop/desktop. Make sure you have the right RAM. Check the documentation.

Sensors and Switches

Every laser printer has a large number of lasers and sensors throughout the machine. The sensors are used to detect a broad range of conditions such as paper jams, empty paper trays, or low toner levels. Many of these switches are really tiny switches that detect open doors and so on. Every now and then though they do become faulty.

Impact Printers

Printers that create an image on paper by physically striking an ink ribbon against the paper's surface are known as impact printers. Impact printers are very old but they are still prominent in offices around America today. They are in offices for two reasons: dot matrix printers have a large installed base in businesses, and they can be used for multipart forms because they actually strike the paper. Impact printers tend to be pretty noisy. Computers that print multipart forms, such as point of sale (POS) machines, use special impact paper that can print receipts in duplicate, triplicate, or more. Dot-matrix printers use a grid, or matrix, of tiny pins, also known as print wires, to strike an inked printer ribbon and produce images on paper. The case that holds the printwires is called a print head. It uses either 9 or 24 pins. 9 pins is known as "draft quality" and 24 pins is known as "letter quality". 24 pins produce better images than 9.

Solid Ink Printers

Solid ink printers use just what you'd expect, solid inks. Solid ink printers use solid sticks of nontoxic "ink" that produce more vibrant color than other print methods. The solid ink is melted and absorbed into the paper fibers; it then solidifies, producing a continuous-tone output. Unlike dye-sublimation printers, all colors are applied to the media in a single pass, reducing the changes of misalignment. Solid ink sticks do not rely on containers (as does ink for inkjet printers) and can be "topped off" midway through a print job by inserting additional color sticks without taking the printer offline. Solid ink cartridges beat the inkjet cartridges in terms of long lasting.

Ozone Filter

The coronas inside laser printers generate ozone (O3). Although not harmful to humans in small amount, tiny concentrations can damage printer components. To counter this problem, most laser printers have a special ozone filter that needs to be vacuumed or replaced periodically.

Erase Lamp

The erase lamp exposes the entire surface of the photosensitive drum to light, making the photosensitive coating conductive. Any electrical charge present in the particles bleeds away into the grounded drum, leaving the surface particles electrically neutral.

Fuser Assembly

The fuser assembly is almost always separate from the toner cartridge. It is usually quite easy to locate, as it is close to the bottom of the toner cartridge and usually has two rollers to fuse the toner. Sometimes the fuser is somewhat enclosed and difficult to recognize because the rollers are hidden from view. The toner is resting on top of the paper after the static charge eliminator has removed the paper's static charge. The toner must be melted to the paper to make the image permanent. Two rollers, a pressure roller and a heated roller, are used to fuse the toner to the paper. The pressure roller presses against the bottom of the page, and the heated roller presses down on the top of the page, melting the toner into the paper. The heated roller has a nonstick coating such as Teflon to prevent the toner from sticking to it.

Imaging Drum

The imaging drum (photosensitive drum) is an aluminum cylinder coated with particles of photosensitive compounds. The drum itself is grounded to the power supply, but the coating is not. When light hits these particles, whatever electrical charge they may have "drains" out through the grounded cylinder.

Dye-Sublimation Printers

The term sublimation means to cause something to change from a solid form into a vapor and then back into a solid. Dye sublimation printers are used mainly for photo printing, high-end desktop publishing, medical and scientific imaging, and other applications for which fine detail and rich color are more important than cost and speed. Dye sublimation uses the CMYK (cyan, magenta, yellow, black) method of color printing. It uses a roll heat-sensitive plastic film embedded with a page-sized sections of cyan (blue), magenta (red), and yellow dye, many also have a section of black dye. A printhead containing thousands of heating elements, capable of precise temperature control, moves across the film, vaporizing the dyes and causing them to soak into specially coated paper underneath before cooling and reverting to a solid form. Documents printed through the dye-sublimation process display continuous-tone images, meaning that the printed image is not constructed of pixel dots but a continuous blend of overlaid differing dye colors. Dye-sublimation printers produce high-quality color output that rivals professional photo-lab processing.

Toner Cartridge

The toner cartridge in a laser printer is so named because of its most obvious activity: supplying the toner that creates the image on the page.

Toner

The toner in a laser printer is a fine powder made up of plastic particles bonded to pigment particles. The toner cylinder charges the toner with a negative charge of between 200 and 500 volts.

Cloud and Remote Printing

There are many applications that you can download to install a virtual printer to your system, such as Google Cloud Print. This will install a virtual print on your system that wraps up your document and sends it out over the Internet or other network to a cloud server.

Printers

There are many printers available on the market and there is a wide variety you can choose from. You can choose from: impact, inkjet, dye-sublimation, thermal, laser, and solid ink.

Thermal Printers

Thermal printers use a heated printhead to create a high-quality image on special or plain paper. You'll see two kinds of thermal printers in use. The first is the direct thermal printer, and the other is the thermal wax transfer printer. Direct thermal printers use a heating element to burn dots into the surface of special heat-sensitive paper. Many retail businesses still use it as a receipt printer, using large rolls of thermal paper housed in a feed assembly that automatically draws the paper past the heating element; some receipt printers can even cut the paper off the roll for you. Thermal wax printer work similarly to dye-sublimation printers, except that instead os using rolls of dye-embedded film, the film is coated with colored wax. Thermal wax printers don't require special papers like dye-sublimation printers do, so they're more flexible and somewhat cheaper to use, but their output isn't quite as good because they use color dithering.

Print to Image

This option lets you save a regular image file, such as BMP, GIF, JPG, PNG, TIFF, and more. Image formats tend to have some problems when being used for documents, text won't scale as well and can't be easily searched/selected/copied, for example, but they are very portable, and can often be viewed with software included in any OS and on many types of devices.

Transfer Corona/Transfer Roller

To transfer the image from the photosensitive drum to the paper, the paper must be given a charge that will attract the toner particles off of the drum and onto the paper. In older printers, the transfer corona, a thin wire, applied a positive charge to the paper, drawing the negatively charged toner particles to the paper. In most laser printers, the transfer corona/roller is outside the toner cartridge, especially in large, commercial-grade machines. The transfer corona/roller is prone to a build up of dirt, toner, and debris through electrostatic attraction, and it must be cleaned. It is also quite fragile, usually finer than a human hair. Most printers with an exposed transfer corona/roller provide a special tool to clean it, but you can also use a cotton swab soaked in 90 percent denatured alcohol. As always, never service any printer without first turning it off and unplugging it from its power source.

Laser Printers

Using a process called electro-photographic imaging, laser printers produce high-quality and high-speed output of both text and graphics. Laser printers rely on the photoconductive properties of certain organic compounds. Photoconductive means that particles of these compounds, when exposed to light, will conduct electricity. Laser printers usually use lasers as a light source because of their precision. some lower-cost printers use LED arrays instead. The first laser printers created only monochrome images; you can also buy a color laser printer, but most laser printers produced today are still monochrome.

Windows GDI and XPS

Windows uses the graphical device interface (GDI) component of the OS to handle print functions. The GDI uses the CPU rather than the printer to process a print job and then sends the completed job to the printer. Windows Vista also introduced a new printing subsystem called the XML Paper Specification (XPS) print path. XPS provides several improvements over GDI, including enhanced color management and better print layout fidelity. The XPS print path requires a driver that supports XPS.

Scanners

You can use a scanner to make digital copies of existing paper photos, documents, drawings, and more. Better scanners give you the option of copying directly from a photographic negative or slide.