Stepper Motor Technology - How Do InkJet Printers Work

Stepper Motor

The printers utilizing inkjet technology were first introduced in the late 1980s and since then have gained much popularity while growing in performance and dropping in price. They are the most common type of computer printers for the general consumer due to their low cost, high quality of output, capability of printing in vivid color, and ease of use. Each printer which works on inkjet technology places extremely small droplets of ink onto paper to create a text or an image. In the personal and small business computer market, inkjet printers currently predominate. Inkjets are usually inexpensive, quiet, reasonably fast, and many models can produce high quality output. Like most modern technologies, the present-day inkjet is built on the progress made by many earlier versions. Among many contributors, Epson, Hewlett-Packard and Canon can claim a substantial share of credit for the development of the modern inkjet technology. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, Hewlett-Packard, Epson, and Lexmark.The typical inkjet printer usually includes inkjet printhead assembly, paper feed assembly, power supply, control circuitry and interface ports.The inkjet printhead assembly contains several components. One of them is the printhead which is the core of the inkjet printer and contains a series of nozzles that are used to spray drops of ink. Another printhead component is the inkjet cartridge or inkjet tank. Depending on the manufacturer and model of the printer, ink cartridges come in various combinations, such as separate black and color cartridges, color and black in a single cartridge or even a cartridge for each ink color. The cartridges of some inkjet printers include the print head itself. The printhead along with the inkjet cartridge/s are moved back and forth across the paper by device called a stepper motor using a special belt. Some printers have an additional stepper motor to park the print head assembly when the printer is not in use which means that the print head assembly is restricted from accidentally moving. The print head assembly uses a stabilizer bar to ensure that movement is precise and controlled. One of the paper feed assembly components is the paper tray or/and paper feeder. Most inkjet printers have a tray that the paper is loaded into. The feeder typically snaps open at an angle on the back of the printer, allowing the paper to be placed in it. Feeders generally do not hold as much paper as a traditional paper tray. A set of rollers pull the paper in from the tray or feeder and advance the paper when the print head assembly is ready for another pass after which another step motor powers the rollers to move the paper in the exact increment needed to ensure a continuous image is printed.While earlier printers often had an external transformer, most printers sold today use a standard power supply that is incorporated into the printer itself. A small but sophisticated amount of circuitry is built into the printer to control all the mechanical aspects of operation, as well as decode the information sent to the printer from the computer. It is connected to the computer by a cable through the interface port. The interface port can be either parallel port, USB port or SCSI port. The parallel port is still used by many printers, but most newer printers use the USB port. A few printers connect using a serial port or small computer system interface (SCSI) port.Different types of inkjet printers exist based on the method they use to deliver the droplets of ink. There are three main inkjet technologies currently used by printer manufacturers. The thermal bubble technology used by manufacturers such as Canon and Hewlett Packard is commonly referred to as bubble jet. In a thermal inkjet printer, tiny resistors create heat, and this heat vaporizes ink to create a bubble. As the bubble expands, some of the ink is pushed out of a nozzle onto the paper. When the bubble collapses, a vacuum is created. This pulls more ink into the print head from the cartridge. A typical bubble jet print head has 300 or 600 tiny nozzles, and all of them can fire a droplet simultaneously. Thermal inkjet technology is used almost exclusively in the consumer inkjet printer market. The ink used is usually water-based, pigment-based or dye-based but the print head is produced usually at less cost than other ink jet technologies.Contrary to the bubble jet technology, the piezoelectric technology, patented by Epson, uses piezo crystals. A crystal is located at the back of the ink reservoir of each nozzle. The crystal receives a tiny electric charge that causes it to vibrate. When the crystal vibrates inward, it forces a tiny amount of ink out of the nozzle. When it vibrates out, it pulls some more ink into the reservoir to replace the ink sprayed out.The continuous inkjet method is used commercially for marking and coding of products and packages. The first patent on the idea is from 1867, by William Thomson. The first commercial model was introduced in 1951 by Siemens. In continuous inkjet technology, a high-pressure pump directs liquid ink from a reservoir through a microscopic nozzle, creating a continuous stream of ink droplets. A piezoelectric crystal causes the stream of liquid to break into droplets at regular intervals. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form. The field is varied according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet. Charged droplets are separated by one or more uncharged “guard droplets” to minimize electrostatic repulsion between neighboring droplets. The charged droplets are then directed (deflected) to the receptor material to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for reuse. Continuous inkjet is one of the oldest inkjet technologies in use and is fairly mature. One of its advantages is the very high velocity (~50 m/s) of the ink droplets, which allows the ink drops to be thrown a long distance to the target. Another advantage is freedom from nozzle clogging as the jet is always in useWhen printing is started, the software application sends the data to be printed to the printer driver which translates the data into a format that the printer can understand and checks to see that the printer is online and available to print. The data is sent by the driver from the computer to the printer via the connection interface. The printer receives the data from the computer. It stores a certain amount of data in a buffer. The buffer can range from 512 KB random access memory (RAM) to 16 MB RAM, depending on the printer model. Buffers are useful because they allow the computer to finish with the printing process quickly, instead of having to wait for the actual page to print. If the inkjet printer has been idle for a period of time, it will normally go through a short cleaning cycle to make sure that the print heads are clean. Once the cleaning cycle is complete, the inkjet printer is ready to begin printing. The control circuitry activates the paper feed stepper motor. This engages the rollers, which feed a sheet of paper from the paper tray / feeder into the printer. A small trigger mechanism in the tray / feeder is depressed when there is paper in the tray or feeder. If the trigger is not depressed, the inkjet printer lights up the "Out of Paper" LED and sends an alert to the computer. Once the paper is fed into the inkjet printer and positioned at the start of the page, the print head stepper motor uses the belt to move the print head assembly across the page. The motor pauses for the merest fraction of a second each time that the print head sprays dots of ink on the page and then moves a tiny bit before stopping again. This stepping happens so fast that it seems like a continuous motion. Multiple dots are made at each stop. It sprays the CMYK (cyan / magenta / yellow / black) colors in precise amounts to make any other color imaginable. At the end of each complete pass, the paper feed stepper motor advances the paper a fraction of an inch. Depending on the inkjet printer model, the print head is reset to the beginning side of the page, or, in most cases, simply reverses direction and begins to move back across the page as it prints. This process continues until the page is printed. The time it takes to print a page can vary widely from printer to printer. It will also vary based on the complexity of the page and size of any images on the page. Once the printing is complete, the print heads are parked. The paper feed stepper motor spins the rollers to finish pushing the completed page into the output tray. Most inkjet printers today use inkjet inks that are very fast-drying, so that you can immediately pick up the sheet without smudging it. Compared to earlier consumer-oriented printers, inkjet printers have a number of advantages. They are quieter in operation than impact dot matrix printers or daisywheel printers. They can print finer, smoother details through higher printhead resolution, and many inkjet printers with photorealistic-quality color printing are widely available. In comparison to more expensive technologies like thermal wax, dye sublimations, and laser printers, the inkjet printers have the advantage of practically no warm-up time and lower cost per page (except when compared to laser printers).The disadvantages of the inkjet printers include flimsy print heads (prone to clogging) and expensive inkjet cartridges. This typically leads value-minded consumers to consider laser printers for medium-to-high volume printer applications. Other disadvantages include ink bleeding, where ink is carried sideways away from the desired location by the capillary effect; the result is a muddy appearance on some types of paper. Most inkjet printer manufacturers also sell special clay-treated paper designed to reduce bleeding. Because the ink used in most inkjet cartridges and ink tanks is water-soluble, care must be taken with inkjet-printed documents to avoid even the smallest drop of water, which can cause severe "blurring" or "running."Besides the well known small inkjet printers for home and office, there is a market for professional inkjet printers; some being for page-width format printing, and most being for wide format printing. "Page-width format" means that the print width ranges from about 8.5" to 37". "Wide format" means that these are inkjet printers ranging in print width from 24" up to 15'. The application of the page-width inkjet printers is for printing high-volume business communications that have a lesser need for flashy layout and color. Particularly with the addition of variable data technologies, the page-width inkjet printers are important in billing, tagging, and individualized catalogs and newspapers. The application of most of the wide format inkjet printers is for printing advertising graphics; a minor application is printing of designs by architects or engineers.

(*About the author - Simon Rogers is a marketing associate for PriceLess-InkJet Cartridges Co., a major reseller of inkjet cartridges, laser toner cartridge and other printing supplies. For more information on printer cartridges, printing technologies, alternative printer supplies and other related issues)