1.14 Compare and contrast differences between the print technologies and the associated imaging process 19

However, three reasons you see impact printers still in use are:

(1) They use continuous tractor feeds and fanfold paper (also called computer paper) rather than individual sheets of paper, making them useful for logging ongoing events or data, (2) they can use carbon paper to print multiple copies at the same time, and (3) they are extremely durable, give little trouble, and seem to last forever.

The seven steps of laser printing are listed next: 1. Processing the image. A laser printer processes and prints an entire page at one time. The page comes to the printer encoded in a language the printer understands and the firmware inside the printer processes the incoming data to produce a Bitmap (a bunch of bits in rows and columns) of the final page, which is stored in the printer's memory. One bitmap image is produced for monochrome images. For color images, one bitmap is produced for each of four colors. (The colors are blue, red, yellow, and black, better known as cyan, magenta, yellow, and black, and sometimes written as CMYK.) 2. Charging or conditioning. During Charging, the drum is conditioned by a roller that places a high uniform electrical charge of -600 V on the surface of the drum. The roller is called the primary charging roller or primary corona, which is charged by a high-voltage power supply assembly. For some printers, a corona wire is used instead of the charging roller to charge the drum. 3. Exposing or writing. A laser beam controlled by motors and a mirror scans across the drum until it completes the correct number of passes. The laser beam is turned on and off continually as it makes a single pass down the length of the drum, once for each raster line, so that dots are exposed only where toner should go to print the image. For example, for a 1200 dots per inch (dpi) printer, the beam makes 1200 passes for every one inch of the drum circumference. For a 1200-dpi printer, 1200 dots are exposed or not exposed along the drum for every inch of linear pass. The 1200 dots per inch down this single pass, combined with 1200 passes per inch of drum circumference, accomplish the resolution of 1200 × 1200 dots per square inch of many laser printers. The laser beam writes an image to the drum surface as a -100 V charge. The -100 V charge on this image area will be used in the developing stage to transmit toner to the drum surface.

4. Developing. The developing cylinder applies toner to the surface of the drum. The toner is charged and sticks to the developing cylinder because of a magnet inside the cylinder. A control blade prevents too much toner from sticking to the cylinder surface. As the cylinder rotates very close to the drum, the toner is attracted to the part of the surface of the drum that has a -100 V charge and repelled from the -600 V part of the drum surface. The result is that toner sticks to the drum where the laser beam has hit and is repelled from the area where the laser beam has not hit. 5. Transferring. In the transferring step (shown in Figure 19-2), a strong electrical charge draws the toner off the drum onto the paper. This is the first step that takes place outside the cartridge and the first step that involves the paper. The soft, black Transfer Roller puts a positive charge on the paper to pull the toner from the drum onto the paper. Then the static charge eliminator (refer again to Figure 19-2) weakens the charges on both the paper and the drum so that the paper does not stick to the drum. The stiffness of the paper and the small radius of the drum also help the paper move away from the drum and toward the fusing assembly. Very thin paper can wrap around the drum, which is why printer manuals usually instruct you to use only paper designated for laser printers. 6. Fusing. The Fuser Assembly uses heat and pressure to fuse the toner to the paper. Up to this point, the toner is merely sitting on the paper. The fusing rollers apply heat to the paper, which causes the toner to melt, and the rollers apply pressure to bond the melted toner into the paper. The temperature of the rollers is monitored by the printer. If the temperature exceeds an allowed maximum value (410 degrees F for some printers), the printer shuts down. 7. Cleaning. A sweeper strip cleans the drum of any residual toner, which is swept away by a sweeping blade. The charge left on the drum is then neutralized. Some printers use erase lamps in the top cover of the printer for this purpose. The lamps use red light so as not to damage the photosensitive drum.

A printer that is able to print on both sides of the paper is called a Duplex Printer or a double-sided printer. Many laser printers and a few inkjet printers offer this feature.

After the front of the paper is printed, a Duplexing Assembly, which contains several rollers, turns the paper around and draws it back through the print process to print on the back of the paper. Alternately, some high-end printers have two print engines so that both sides of the paper are printed at the same time.

The charging, exposing, developing, and cleaning steps use the printer components that undergo the most wear. To make the printer last longer, these steps are done inside a removable cartridge that can be replaced. For older printers, all four steps were done inside one cartridge.

For newer printers, the cleaning, charging, and exposing steps are done inside the image drum cartridge. The developing cylinder is located inside the toner cartridge. The transferring is done using a Transfer Belt that can be replaced, and the fusing is done inside a fuser cartridge

Other printer parts that might need replacing include the Pickup Roller that pushes forward a sheet of paper from the paper tray and the Separation Pad (also called separate pad) that keeps more than one sheet of paper from moving forward.

If the pickup roller is worn, paper misfeeds into the printer. If the separation pad is worn, multiple sheets of paper will be drawn into the printer. Sometimes you can clean a pickup roller or separation pad to prolong its life before it needs replacing.

An inkjet printer (see Figure 19-3) uses a type of ink-dispersion printing and doesn't normally provide the high-quality resolution of laser printers.

Inkjet printers are popular because they are small and can print color inexpensively. Most inkjet printers today can print high-quality photos, especially when used with photo-quality paper

Laser printers require the interaction of mechanical, electrical, and optical technologies.

Laser printers work by placing toner on an electrically charged rotating drum (sometimes called the imaging drum) and then depositing the toner on paper as the paper moves through the system at the same speed the drum is turning.

The impact paper used by Impact Printers comes as a box of fanfold paper or in rolls (used with receipt printers). When the paper is nearing the end of the stack or roll, a color on the edge alerts you to replace the paper.

Occasionally, you should replace the ribbon of a dot matrix printer. If the print head fails, check on the cost of replacing the head versus the cost of buying a new printer. Sometimes, the cost of the head is so high it's best to just buy a new printer.

Thermal printers use heat to create an image. Two types of thermal printers are a direct thermal printer and a thermal transfer printer.

The older direct thermal printer burns dots onto special coated paper, called thermal paper, as was done by older fax machines. The process requires no ink and does not use a ribbon. Direct thermal printers are often used as receipt printers that use rolls of thermal paper (see Figure 19-7). The printed image can fade over time.

An Impact Printer creates a printed page by using some mechanism that touches or hits the paper. The best-known impact printer is a dot matrix printer, which prints only text that it receives as raw data. It has a print head that moves across the width of the paper, using pins to print a matrix of dots on the page.

The pins shoot against a cloth ribbon, which hits the paper, depositing the ink. The ribbon provides both the ink for printing and the lubrication for the pinheads. The quality of the print is poor compared with other printer types.

An inkjet printer uses a Print Head that moves across the paper, creating one line of the image with each pass.

The printer puts ink on the paper using a matrix of small dots.

Inkjet printers tend to smudge on inexpensive paper, and they are slower than laser printers. If a printed page later gets damp, the ink can run and get quite messy.

The quality of the paper used with inkjet printers significantly affects the quality of printed output. You should use only paper that is designed for an inkjet printer, and you should use a high-grade paper to get the best results.

By using these multiple cartridges inside laser printers, the cost of maintaining a printer is reduced. You can replace one cartridge without having to replace them all.

The toner cartridge needs replacing the most often, followed by the image drum, the fuser cartridge, and the transfer assembly, in that order.

A thermal transfer printer uses a ribbon that contains wax- based ink. The heating element melts the ribbon (also called foil) onto special thermal paper so that it stays glued to the paper as the feed assembly moves the paper through the printer.

Thermal transfer printers are used to print receipts, barcode labels, clothing labels, or container labels.

When purchasing an inkjet printer, look for the kind that uses two or four separate cartridges. One cartridge is used for black ink. Three cartridges, one for each color, give better quality color than one cartridge that holds all three colors. Some low-end inkjet printers use a single three-color cartridge and don't have a black ink cartridge.

These printers must combine all colors of ink to produce a dull black. Having a separate cartridge for black ink means that it prints true black and, more important, does not use the more expensive colored ink. To save money, you should be able to replace an empty cartridge without having to replace all cartridges.

The major categories of printer types include

laser, inkjet (ink dispersion), impact, and thermal printers

Inkjet printers include

one or more Ink Cartridges to hold the different colors of ink for the printer.

A laser printer

type of electro-photographic printer that can range from a small, personal desktop model to a large, network printer capable of handling and printing large volumes continuously.