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Understanding Print Technologies and Imaging Processes Several types of printers are available on the market today. As with all other computer components, there have been significant advancements in printer technology over the years. Most of the time, when faced with the decision of purchasing a pri...

Understanding Print Technologies and Imaging Processes Several types of printers are available on the market today. As with all other computer components, there have been significant advancements in printer technology over the years. Most of the time, when faced with the decision of purchasing a printer, you’re going to be weighing performance versus cost. Some of the higher-quality technologies, such as color laser238printing, are relatively expensive for the home user. Other technologies are less expensive but don’t provide the same level of quality. In the following sections, you will learn about the various types of print technologies that you will see as a technician as well as their basic components and how they function. Specifically, we are going to look at five classifications of classic printing: impact, inkjet, laser, thermal, and virtual, and then finish up with a primer on 3D printing. Impact Printers The most basic type of printer is in the category known as an impact printer. Impact printers, as their name suggests, use some form of impact and an inked printer ribbon to make an imprint on the paper. Impact printers also use a paper feed mechanism called a tractor feed that requires special paper. Perhaps you’ve seen it before—it’s continuous feed paper with holes running down both edges. There are two major types of impact printers: daisy-wheel and dot- matrix. Each type has its own service and maintenance issues. Daisy-Wheel Printers The first type of impact printer to know about is the daisy-wheel printer. This is one of the oldest printing technologies in use. These impact printers contain a wheel (called the daisy wheel because it looks like a daisy) with raised letters and symbols on each “petal” (see Figure 5.1). When the printer needs to print a character, it sends a signal to the mechanism that contains the wheel. This mechanism is called the print head. The print head rotates the daisy wheel until the required character is in place. An electromechanical hammer (called a solenoid) then strikes the back of the petal containing the character. The character pushes up against an inked ribbon that ultimately strikes the paper, making the impression of the requested character. Figure 5.1 A daisy-wheel printer mechanism 239 Daisy-wheel printers were among the first types of impact printer developed. Their speed is rated by the number of characters per second (cps) they can print. The earliest printers could print only two to four characters per second. Aside from their poor speed, the main disadvantage of this type of printer is that it makes a lot of noise when printing—so much so, in fact, that special enclosures were developed to contain the noise. There is also no concept of using multiple fonts; the font is whatever the character on the wheel looks like. The daisy-wheel printer has a few advantages, of course. First, because it is an impact printer, you can print on multipart forms (like carbonless receipts), assuming that they can be fed into the printer properly. Sometimes, you will hear this type of paper referred to as impact paper. Second, it is relatively inexpensive compared to the price of a laser printer of the same vintage. Finally, the print quality is easily readable; the level of quality was given a name: letter quality (LQ). Today, LQ might refer to quality that’s better than an old-school typewriter (if you’re familiar with them) but not up to inkjet standards. Dot-Matrix Printers The other type of impact printer to understand is the dot-matrix printer. These printers work in a manner similar to daisy-wheel printers, but instead of a spinning, character-imprinted wheel, the print head contains a row of pins (short, sturdy stalks of hard wire). These pins are triggered in patterns that form letters and numbers as the print head moves across the paper (see Figure 5.2). Figure 5.2 Formation of images in a dot-matrix printer The pins in the print head are wrapped with coils of wire to create a solenoid and are held in the rest position by a combination of a small magnet and a spring. To trigger a particular pin, the printer controller sends a signal to the print head, which energizes the wires around the appropriate print wire. This turns the print wire into an electromagnet, which repels the print pin, forcing it against the ink ribbon and making a dot on the paper. The arrangement of the dots in columns and rows creates the letters and numbers that you see on the page. Figure 5.2 illustrates this process. 240 The main disadvantage of dot-matrix printers is their image quality, which can be quite poor compared to the quality produced with a daisy wheel. Dot-matrix printers use patterns of dots to make letters and images, and the early dot-matrix printers used only nine pins to make those patterns. The output quality of such printers is referred to as draft quality—good mainly for providing your initial text to a correspondent or reviser. Each letter looked fuzzy because the dots were spaced as far as they could be and still be perceived as a letter or image. As more pins were crammed into the print head (17-pin and 24-pin models were eventually developed), the quality increased because the dots were closer together. Dot-matrix technology ultimately improved to the point that a letter printed on a dot-matrix printer was almost indistinguishable from daisy-wheel output. This level of quality is known as near letter quality (NLQ). Dot-matrix printers are noisy, but the print wires and print head are covered by a plastic dust cover, making them quieter than daisy-wheel printers. They also use a more efficient printing technology, so the print speed is faster (typically starting around 72 cps). Some dot-matrix printers (like the Epson DFX series) can print at close to a page per second! Finally, because dot-matrix printers are also impact printers, they can use multipart forms. Because of these advantages, dot-matrix printers quickly made daisy-wheel printers obsolete. Inkjet Printers One of the most popular types of printers in use today is the inkjet printer. As opposed to impact printers, which strike the page, these printers spray ink on the page to form the image. Inkjet printers typically use a reservoir of ink, a pump, and a nozzle to accomplish this. Older inkjet printers were messy, noisy, and inefficient, but the technology is good enough now that you see plenty of photo printers using inkjet technology. You might also hear these types of printers referred to as bubble-jet printers, but that term is copyrighted by Canon. You can think of inkjets as spraying droplets of ink in a very high-definition dot-matrix pattern, although printer manufacturers would likely scoff at the comparison to an older technology. In the following sections, you will learn the parts of an inkjet printer as well as how inkjet printers work. Parts of a Typical Inkjet Printer Inkjet printers are simple devices. They contain very few parts (even fewer than dot-matrix printers) and, as such, are inexpensive to manufacture. It’s common today to have a $40 to $50 inkjet printer with print quality that rivals that of basic laser printers. 241 The printer parts can be divided into the following categories: Print head/ink cartridge Head carriage, belt, and stepper motor Paper feed mechanism Control, interface, and power circuitry Why So Cheap? The cost of inkjet printers is pretty low—one would think that the printer companies make very little money on them (which is true). So why do they price them so low? The answer is that printer companies make the vast majority of their profits off of ink cartridge sales. They figure that if they can get you into their printer, you will buy their ink refills—which is true—so you are then a captive consumer. Ink cartridges are very cheap to produce and have a high profit margin. Print Head/Ink Cartridge The first part of an inkjet printer is the one that people see the most: the print head. This part of a printer contains many small nozzles (usually 100 to 200) that spray the ink in small droplets onto the page. Many times, the print head is part of the ink cartridge, which contains a reservoir of ink and the print head in a removable package. Most color inkjet printers include multiple print heads. Either there will be one for the black cartridge and one for the color one, or there will be one for each of the CMYK (cyan, magenta, yellow, and black) print inks. The print cartridge must be replaced as the ink supply runs out. Inside the ink cartridge are several small chambers. At the top of each chamber are a metal plate and a tube leading to the ink supply. At the bottom of each chamber is a small pinhole. These pinholes are used to spray ink on the page to form characters and images as patterns of dots, similar to the way a dot-matrix printer works but with much higher resolution. There are two methods of spraying the ink out of the cartridge. Hewlett-Packard (HP) popularized the first method: When a particular chamber needs to spray ink, an electric signal is sent to the heating element, energizing it. The elements heat up quickly, causing the ink to vaporize. Because of the expanding ink vapor, the ink is pushed out of the pinhole and forms a bubble. As the vapor expands, the bubble eventually gets large enough to break off into a droplet. The rest of the ink is pulled back into the chamber by the surface tension of the ink. When another drop needs to be sprayed, the process begins again. The second method, developed by Epson, uses a piezoelectric element (either a small rod or a unit that looks like a miniature drum head) that flexes when energized. The outward flex pushes the ink from the nozzle; on the return, it sucks more ink from the reservoir. 242 When the printer is done printing, the print head moves back to its maintenance station. The maintenance station contains a small suction pump and ink-absorbing pad. To keep the ink flowing freely, before each print cycle, the maintenance station pulls ink through the ink nozzles using vacuum suction. The pad absorbs this expelled ink. The station serves two functions: to provide a place for the print head to rest when the printer isn’t printing and to keep the print head in working order. Head Carriage, Belt, and Stepper Motor Another major component of the inkjet printer is the head carriage and the associated parts that make it move. The print head carriage is the component of an inkjet printer that moves back and forth during printing. It contains the physical as well as electronic connections for the print head and (in some cases) the ink reservoir. Figure 5.3 shows an example of a head carriage. Note the clips that keep the ink cartridge in place and the electronic connections for the ink cartridge. These connections cause the nozzles to fire, and if they aren’t kept clean, you may have printing problems. Figure 5.3 A print head carriage (holding two ink cartridges) in an inkjet printer The stepper motor and belt make the print head carriage move. A stepper motor is a precisely made electric motor that can move in the same very small increments each time it is activated. That way, it can move to the same position(s) time after time. The motor that makes the print head carriage move is also often called the carriage motor or carriage stepper motor. Figure 5.4 shows an example of a stepper motor. 243 Figure 5.4 A carriage stepper motor In addition to the motor, a belt is placed around two small wheels or pulleys and attached to the print head carriage. This belt, called the carriage belt, is driven by the carriage motor and moves the print head back and forth across the page while it prints. To keep the print head carriage aligned and stable while it traverses the page, the carriage rests on a small metal stabilizer bar. Figure 5.5 shows the stabilizer bar, carriage belt, and pulleys. 244 Paper Feed Mechanism In addition to getting the ink onto the paper, the printer must have a way to get the paper into the printer. That’s where the paper feed mechanism comes in. The paper feed mechanism picks up paper from the paper drawer and feeds it into the printer. This component consists of several smaller assemblies. First are the pickup rollers (see Figure 5.6), which are several rubber rollers with a slightly flat spot; they rub against the paper as they rotate and feed the paper into the printer. They work against small cork or rubber patches known as separator pads (see Figure 5.7), which help keep the rest of the paper in place so that only one sheet goes into the printer. The pickup rollers are turned on a shaft by the pickup stepper motor. Figure 5.5 Stabilizer bar, carriage belt, and pulleys in an inkjet printer Figure 5.6 Inkjet pickup rollers Figure 5.7 Inkjet separator pads 245  Clean pickup rollers (and other rubber rollers) with mild soap and water, not with alcohol. Alcohol can dry out the rollers, making them brittle and ineffective. Sometimes the paper that is fed into an inkjet printer is placed into a paper tray, which is simply a small plastic tray in the front of the printer that holds the paper until it is fed into the printer by the paper feed mechanism. On smaller printers, the paper is placed vertically into a paper feeder at the back of the printer; it uses gravity, in combination with feed rollers and separator pads, to get the paper into the printer. No real rhyme or reason dictates which manufacturers use these different parts; some models use them, and some don’t. Generally, more expensive printers use paper trays because they hold more paper. Figure 5.8 shows an example of a paper tray on an inkjet printer. Figure 5.8 A paper tray on an inkjet printer The final parts of the paper feed mechanism are the paper feed sensors. These components tell the printer when it is out of paper as well as when a paper jam has occurred during the paper feed process. Figure 5.8 shows an example of a paper feed sensor. Being able to identify the parts of an inkjet printer is an important skill for an A+ candidate. In Exercise 5.1, you will identify the parts of an inkjet printer. For this exercise, you’ll need an inkjet printer.  Many of the exercises in this chapter require printer hardware. If you don’t have the proper hardware on which to practice, you can find many helpful videos online showing how to identify parts and install and perform maintenance on printers. Sites such as ifixit.com and youtube.com are good places to start. 246 Figure 5.9 A paper feed sensor on an inkjet printer Control, Interface, and Power Circuitry The final component group is the electronic circuitry for printer control, printer interfaces, and printer power. The printer control circuits are usually on a small circuit board that contains all the circuitry to run the stepper motors the way the printer needs them to work (back and forth, load paper and then stop, and so on). These circuits are also responsible for monitoring the health of the printer and for reporting that information back to the PC. The second power component, the interface circuitry (commonly called a port), makes the physical connection to whatever signal is coming from the computer (USB, serial, network, infrared, etc.) and also connects the physical interface to the control circuitry. The interface circuitry converts the signals from the interface into the data stream that the printer uses. The last set of circuits the printer uses is the power circuits. Essentially, these conductive pathways convert 110V (in the United States) or 220V (in most of the rest of the world) from a standard wall outlet into the voltages that the inkjet printer uses, usually 12V and 5V, and distribute those voltages to the other printer circuits and devices that need it. This is accomplished through the use of a transformer. A transformer, in this case, takes the 110V AC current and changes it to 12V DC (among others). This transformer can be either internal (incorporated into the body of the printer) or external. Either design can be used in today’s inkjets, although the integrated design is preferred because it is simpler and doesn’t show the bulky transformer. The Inkjet Printing Process Before you print to an inkjet printer, you must ensure that the device is calibrated. Calibration is the process by which a device is brought within functional specifications. For example, inkjet printers need their print heads aligned so that they print evenly and don’t print funny-looking letters and unevenly spaced lines. The process is part of the installation for all inkjet printers. Printers will typically run a calibration routine every time you install new ink cartridges. You will only need to manually initiate a calibration if the printing alignment appears off. Just as with other types of printing, the inkjet printing process consists of a set of steps that the printer must follow in order to put the data onto the page being printed. The following steps take place whenever you click the Print button in your favorite software (like Microsoft Word or Google Chrome): You click the Print button (or similar) that initiates the printing process. The software from which you are printing sends the data to be printed to the printer driver that you have selected.  The function and use of the printer driver are discussed later in this chapter. 248The printer driver uses a page-description language to convert the data being printed into the format that the printer can understand. The driver also ensures that the printer is ready to print. The printer driver sends the information to the printer via whatever connection method is being used (USB, network, serial, and so on). The printer stores the received data in its onboard print buffer memory. A print buffer is a small amount of memory (typically 512 KB to 16 MB) used to store print jobs as they are received from the printing computer. This buffer allows several jobs to be printed at once and helps printing to be completed quickly. If the printer has not printed in a while, the printer’s control circuits activate a cleaning cycle. A cleaning cycle is a set of steps the inkjet printer goes through to purge the print heads of any dried ink. It uses a special suction cup and sucking action to pull ink through the print head, dislodging any dried ink or clearing stuck passageways. Once the printer is ready to print, the control circuitry activates the paper feed motor. This causes a sheet of paper to be fed into the printer until the paper activates the paper feed sensor, which stops the feed until the print head is in the right position and the leading edge of the paper is under the print head. If the paper doesn’t reach the paper feed sensor in a specified amount of time after the stepper motor has been activated, the Out Of Paper light is turned on and a message is sent to the computer. Once the paper is positioned properly, the print head stepper motor uses the print head belt and carriage to move the print head across the page, little by little. The motor is moved one small step, and the print head sprays the dots of ink on the paper in the pattern dictated by the control circuitry. Typically, this is either a pattern of black dots or a pattern of CMYK inks that are mixed to make colors. Then the stepper motor moves the print head another small step; the process repeats all the way across the page. This process is so quick, however, that the entire series of starts and stops across the page looks like one smooth motion. At the end of a pass across the page, the paper feed stepper motor advances the page a small amount. Then the print head repeats step 8. Depending on the model, either the print head returns to the beginning of the line and prints again in the same direction only or it moves backward across the page so that printing occurs in both directions. This process continues until the page is finished. Once the page is finished, the feed stepper motor is actuated and ejects the page from the printer into the output tray. If more pages need to print, the process for printing the next page begins again at step 7. Once printing is complete and the final page is ejected from the printer, the print head is parked (locked into rest position) and the print process is finished. 249 Some nicer models of inkjet printers have a duplexing assembly attached to them, either at the back of the printer or inside it. It’s used for two-sided printing. After the first page is printed, it’s fed into the duplexing assembly, turned over, and fed back into the paper feed assembly. Then the second page can be printed on the back side of the original piece of paper. It’s a fancy attachment that gives your inkjet more functionality.