|
||
 |
||
|
| Spray It, Don't Say It, With Inkjet Printers |
 Email This
 Print ThisView My Personal Library |
|
Computing Basics March 1994 • Vol.5 Issue 3 |
Spray It, Don't Say It, With Inkjet Printers Thanks to high-quality print and reasonable prices, inkjets are finally coming of age. | ||
|
Listen. Can you hear it? It's the sound of numerous new printer owners kicking themselves for not buying an inkjet printer. In recent years the sales of inkjet printers have quietly been growing by leaps and bounds. In fact, in 1993 the number of sales of inkjet printers almost caught up to that of laser printers. (See Figure 1.) And according to Samuel Shukovsky, spokesperson at the market research company BIS Strategic Decisions, that growth will continue. BIS now projects that by 1997 inkjet printers will replace the ever -popular dot matrix printer at the top of the heap with 55% of all printer sales. Who would have thought that these silent, unassuming printers, which were outdone by laser printers when they both were introduced in 1984, could now be making inroads into a market where they once barely made a showing? But thanks to high-quality print and reasonable prices, inkjets are finally coming of age. In the next few pages we will take a closer look at inkjet printers—how they print, how they compare to other printing types, and why they seem to be gaining in popularity.  Spray Printing Inkjet printers have a way of putting images on paper all their own. They never come in contact with the page, like dot matrix printers, which create letters by striking small, blunt-end pins through a ribbon that transfers ink onto paper. They also don't use fancy light shows like laser printers, which use reflected laser beams to place an image on a page. Instead, inkjets spray print. Jeremy James, spokesperson for Hewlett-Packard Co., says a set of nozzles, each thinner than a human hair, is lined up vertically on a printing head, or the part of the printer that puts the image on the paper. Each of the nozzles is connected to the printer's central ink supply located in an ink cartridge. As the printhead moves past the surface of your page, Edie Dees, group product manager at Epson America Inc., says the printer squirts liquid ink through the nozzles in the form of ink drops. These ink drops are then projected onto a page to make an image or text. But unlike the haphazard droplet patterns that spray painting places on its recipient, spray printing is very precise. Inkjet images are made up of tiny mosaics of dots. Each drop equals one of these dots. So it's very important that each drop of ink has to be placed in an exact spot to complete the picture. Basically, that is the method that almost all inkjet printers use. It's called drop-on-demand, because as the printhead passes over the paper, computer circuitry tells the nozzles to create as many drops as are needed to form the image. However, different brands put different twists on the process. Many inkjet printers use heat to push the ink out of the nozzles in a method called thermal printing. (See Figure 2.) The tip of each nozzle is encircled by a small piezoelectric crystal. When these crystals are heated, they expand and contract, forcing out drops of ink at such a speed that they are propelled onto the page. Canon's Bubble Jet printers also use a form of this thermal process, called Bubble Jet printing. But instead of heating the nozzle, they heat the ink channel, which brings ink from the ink supply to the nozzle. (See Figure 3.) To fire a drop, an electronic circuit starts the ink channel's heater. It heats up quickly and forms a bubble in the ink channel. When this bubble bursts, it forces a drop of ink out of the nozzle and onto the page. Then a vacuum effect causes more bubbles to be drawn into the nozzles. Epson's printers don't use this thermal process. In fact, there is no heat involved. The thermal mechanism is replaced by electricity, Dees says. Called piezo printing, a small piezoelectric crystal is electrically charged causing it to vibrate. She says this vibration, in turn, causes an actuator or multiple actuators to push ink out of the ink cavity, through nozzles, and onto the page. There is one last type of inkjet printing that you may come across that doesn't fall in the drop-on-demand category—continuous flow printing. This is a more complex process. Just as the name implies, the ink constantly flows through nozzles. However, before they are squirted onto the page, they are sent through a charge chamber that gives individual droplets electrical charges. The charge varies, which means if droplets are not supposed to be sprayed on the page (for unprinted areas) they are not given a charge. The charged droplets then are sent to the page and uncharged drops are sent back to be reused. Because the image is sprayed continually, the nozzle stays in one place and the page is moved in front of the ink. For this reason, you won't find many continuous flow printers (if any) for your PC. An Uphill Battle The technology seems simple enough. Let's face it—the idea of spraying ink on paper is not new. Nevertheless, the inkjet's battle to compete has been all uphill. Dot matrix printers had the early lead in dominating the printer market because they were so inexpensive. However, their print quality left something to be desired. So for those users who wanted high -quality images and could afford it, the laser printers were the technology of choice. Inkjet printers also could print quality images, but people weren't as receptive to inkjet printing because the technology had a few glitches when it first was introduced. Most of the problems were a result of the liquid ink that early inkjet printers used (dot matrix printers use ribbons like typewriters, and laser printers use a dry ink called toner). In the early 80s, some users had problems with clogged printheads, Dees says. "The ink would not be completely purged out of the nozzle, so the remainder would dry in the nozzle and clog it," she says. Another problem with the ink was that it was water-soluble. So as soon as the printed page came in contact with moisture, the ink would run. Occasionally thermal inkjet printers would have problems with satellites. No, these satellites didn't fly around the printer or the office. They surrounded the dots on the page, making images look a little blurry. Dees says satellites are formed from a small ink mist that sometimes follows ink drops out of the nozzles. And just as when you take a fountain pen and drop an ink droplet onto a napkin it will spread, so could the inkjet ink on the paper, Dees says. When this spreading phenomenon, called wicking, occurred in large proportions it could also cause the images to slightly blur. But most of these technical difficulties have been resolved. New ink compositions that are far superior to the older ink formulas have lessened problems with smearing or extensive wicking. Progress has also been made on clogging and satellites. Some companies have placed ink in sealed cartridges along with nozzles, so you replace all the working mechanisms every time you replace the ink. Other companies have various technologies that purge and clean the nozzles using a special cleaning process, or cap the heads of the nozzles so they are not open to the air to dry. How They Measure Up Because the inkjet vendors have cleared up most of the early problems, they have made the inkjet printer a more competitive player in the printer market. If you compare the technologies, inkjets certainly outshine dot matrix printers. First of all, inkjet printers are quieter than dot matrix printers. Dot matrix printers are impact printers with pins actually making contact with the ribbon, Dees says, and therefore make noise. Inkjets, which are non -impact printers, are virtually silent. Inkjet printers can also make darker, smoother, and more fully formed images, Dees says. They have a higher level of clarity and fineness of detail when producing an image. In fact, James says, inkjets can produce print quality near that of a laser printer. The makeup of the inkjet printer also lends itself as an excellent choice for color printing. James says separate ink cartridges are used for the primary colors that make up millions of color possibilities—cyan, yellow, magenta, and black. The inkjet printer intelligently takes the information that is being delivered from the computer and chooses the appropriate color to squirt onto the page and mix with the other colors in order to create a full palette of colors. But inkjet printers still have a few disadvantages to consider. Because the inkjet is not an impact printer, you can not print carbon copies. And because many inkjets are cut-sheet printers (which means you feed in one separate sheet at a time), you can not print on tractor-feed paper that is perforated together. Here the dot matrix wins out. Unfortunately the inkjet can not print at its highest quality on certain types of paper. While an inkjet can print well on smooth, crisp paper, more absorbent paper causes it to wick at a higher rate. Coarse, rough-surfaced paper distributes the ink drops unevenly and the image doesn't look as sharp. Some inkjet printers also are not the fastest performers in the printer race. You have to give inkjet printers time to warm up and prepare the ink before you start printing. In some printers, this can take up to 10 minutes after you plug them in. Inkjets also print more slowly than other printers. Dees says dot matrix printers in the same price range as desktop inkjet printers print an average of 250 characters per second, while inkjets print around 150 to 220 characters per second. Low-end laser printers can print four to six pages per minute, which leaves the inkjet behind at one and a half to two pages a minute. But all these things aside, probably the thing that has made inkjets the most competitive is the fact that buyers can get near-laser quality at near-dot matrix prices. "In the last couple of years, inkjets have gotten down in price to a certain sweet spot in the dot matrix market in terms of price," James says. While entry-level dot matrix printers have always had the lowest price models, priced around $150 to $250, you can now find black and white inkjet printers starting at about $50 more, at prices between $250 to $400. Laser printers have always topped the market—with prices now starting at $500 or $600— but most companies are pricing inkjet printers at least 50% less. This way, even though the print quality is not the same as a laser printer, James says the inkjet printers will be attractive to buyers. Interested in color? For a little bit more money than a black and white inkjet, you can buy a color inkjet. For example, Hewlett-Packard's DeskJet 500C lists for $485, James says. The color printing is another big bonus, even if you print primarily in black and white. You can have the color capability for a little more money for the times you are going to need it. Decisions, Decisions If you are a first-time buyer looking for a printer, take into consideration the price and the performance of each type of printing technology. Just because inkjet printers seem to be on the rise, doesn't mean you necessarily need to buy one. Weigh which options are most important. Do you need to make carbon copies? Do you need the high quality of a laser printer? Would you ever use color printing? How much are you able to spend? Make an educated choice. You certainly don't want to be kicking yourself down the line for not making the right decision.  by Cindy Krushenisky |
|
Home Copyright & Legal Information Privacy Policy Site Map Contact Us