Dot matrix printer
Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facing the ribbon and the paper is a small guide plate (often made of an artificial jewel such as sapphire or ruby [1]) pierced with holes to serve as guides for the pins. The moving portion of the printer is called the print head, and when running the printer as a generic text device generally prints one line of text at a time. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.
These machines can be highly durable, but eventually wear out. Ink invades the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires. Eventually, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read.
Although nearly all inkjet, thermal, and laser printers produce dot matrices, in common parlance these are seldom called "dot matrix" printers, to avoid confusion with dot matrix impact printers.
Typical output from a dot matrix printer operating in draft mode. This entire image represents an area of printer output approximately 4.5 cm x 1.5cm (1.75 x 0.6 inches) in size.
Details Of Dot Matrix
Before we discuss the pros, cons and new ideas in dot matrix printing, let's start with the basics. We'll take a look at how the dot matrix printing process works.
The machine at the top of the printer family tree is the typewriter. It has been relegated to an obscure corner of most offices, just like many family patriarchs get stuck in a rocking chair in the corner. However, modern printers are still trying to live up to the legacy left behind by the typewriter. The documents produced on a typewriter were of letter quality, the print quality adopted as a standard by the business world. Laser printers now print at the letter quality standard. (Laser printing uses a process similar to that of photocopying.)
Thinking in simple terms, a dot matrix printer operates like a typewriter. Both machines strike an inked ribbon which, in turn, strikes the paper. This characteristic places dot matrix printers in the category of impact printers.
The difference between typewriters and dot matrix printers lies in the device that strikes the ribbon. As you know, a typewriter uses hammers with fully-formed letters. However, if you look inside a dot matrix printer you won't find any letters. The printer forms letters with a series of pins or wires that strikes the ribbon. Each character is printed within a cell made up of rows and columns of the dots made by the pins; the rows and columns form a matrix. The number of pins in the printhead, the device that moves across the page and contains the pins, like the carriage of a typewriter, determines the number of dots per cell.
As common sense indicates, the more dots, or pins, you have in a cell, the better the print quality. Since complete letters aren't formed, there are always gaps between the tiny dots. The more pins in the printhead, the closer the dots will be and the more continuous the look of the letters. The early dot matrix printers had only nine pins, a cell nine pins horizontally by nine pins vertically for a matrix of 81 dots per character.
A method was soon devised to improve on the quality while still using just nine pins. The answer was to have the printer make two passes, printing a complete set of dots each time. This double-take creates a matrix of 18 dots by 18 dots. Manufacturers assigned the term near letter quality or NLQ to the print mode using two passes to complete a line of characters.
Today, most dot matrix printers have more than one print mode. The fastest is draft mode, which offers great speed but fairly low print quality. Draft mode, as the name implies, is usually used to print rough drafts of documents for early proofing. NLQ mode offers better print quality and slower print times since the printer must make two passes on each line. Most 24-pin printers have letter quality or LQ mode, the highest quality print. As with nine-pin printers, the LQ mode is slower than draft mode, but it offers better print quality. A topic of debate is whether a dot matrix printer's LQ is as good as a laser printer's LQ. Generally, a laser printer is believed to offer the highest quality print.
Another common printing expression is dots per inch, or dpi. This is the measurement used when talking about resolution in graphics printing. To understand dpi, you must forget the number of dots in each character cell and think about the number of dots in an inch. However, letter printing and graphics printing do have something in common. In both cases, the more dots you have, the better print quality you have. With a higher dpi number, graphics will be clearer and have a higher resolution.
A typical nine-pin printer has 240 dots horizontally and 216 dots vertically per inch. Many 24-pin printers have 360 dpi, meaning there are 360 dots horizontally and vertically. What does this dpi stuff mean in the real world? Well, to give you an idea of some comparisons, the typesetter used to print this magazine has 2,400 dpi. Most laser printers offer around 600 to 1,000 dpi.
Dot matrix printers are usually of great interest to novice computer users since novices are often low-budget computer users. You can find a good dot matrix printer for around $300 or $400. This low cost is the main advantage dot matrix has over other types of printing since a laser printer will cost around $800.
According to Bob Adam, vice president of marketing for Citizen America Corp., the savings aren't all up-front with dot matrix printers. He says the average cost per page when using a laser printer is about 3 cents. The cost per page for dot matrix printing, he says, is about 8/10 of a cent. Cost per page refers to the cost of consumable printing supplies such as inked ribbons in dot matrix printers and toner cartridges in laser printers.
Adam says the low cost of the printers makes them attractive to two groups of users. The new users we've already discussed like the low cost and small space requirements of dot matrix printers. Users who are part of a work group often share one laser printer for all of their printing needs. Adam says many of these users want a dot matrix printer for their personal print jobs.
"(They like dot matrix printers) because of making their own personal hard copies, confidential material, just the convenience of being able to print some documents on their own printer . . . without having to race down to where the laser (printer) is," he says.
As was already mentioned, durability is another strong point for dot matrix printers. If the printers don't live up to their tough reputation, the manufacturers are usually there to help. Citizen, for example, has a two-year warranty on its printers. Citizen pays the bill for anything you put into the printer besides paper and ribbon. Dot matrix printers seem to last forever, and they're quite versatile in the various printing jobs they can handle. The printers can print on many kinds of paper, letterhead, envelopes, and overhead slides, and they can print either graphics or regular text.
According to P.J. Johnston, a product manager at Panasonic, the versatility of dot matrix printers attracts many buyers.
"If you have diversified needs, then definitely dot matrix would be the way to go," she says. "It is the most diversified of the products, allowing you to do graphics, spreadsheets, labels, word processing, etc."
Spreadsheets are grid-like programs used for financial data and reports.
One feature crucial for many users is the ability of dot matrix printers to print on multipart forms. These are the carbon-paper forms that allow you to make several copies of a document. Multipart forms work because of the pressure exerted on the top copy that allows the marks to go through to the various sheets. Nonimpact printers, such as laser printers, never touch the paper and, thus, can't exert the pressure needed to make several copies. Dot matrix printers work like a typewriter, striking the paper so they can utilize carbon-paper forms.
"Sure, with a nonimpact printer you can do five of the same page if you will, but that's five separate pages,"
Are there any drawbacks to this seemingly wonderful method of printing? Yes, traditionally there are two major ones.
Dot matrix printers are notoriously noisy. Because they strike the paper, have a mechanical paper feed mechanism, and have a moving printhead, they can be loud enough to drown out phone conversations and anything else in their immediate area.
"To be honest with you,"
Neither one sounds like a very good option for a busy office, does it? Dot matrix disputes commonly arise in offices when someone's about to make a big deal on the phone, and the guy at the next desk decides to start printing his list of contacts for the last five years. Obviously, "good will toward man" and dot matrix printers don't always coexist.
The print quality of dot matrix printers is also a drawback. The pin-method of printing cannot realistically compete with the fine quality offered by nonimpact printers.
Recent innovations have almost made both these drawbacks things of the past. Let's take a look at what factors are helping dot matrix printers make the switch from steady player to reliable All-Star.
Possibly the most annoying aspect of dot matrix printers is their very obvious noise. Anyone who has used one of these printers knows that the tranquility of the office will be destroyed whenever you decide to turn out a document. According to Bob Adam, early dot matrix printers operated at about 70 decibels. For some comparison, normal talking is about 58 decibels and a typical alarm clock goes off at 80 decibels.
"We're down to a place now where we're competing as far as being unobtrusive," Adam says. "People want to be able to do some computing and, then, when they send their print job . . . to their printer, maybe they want to do something different like talk on the telephone and maybe it's right at their desk. Before this quiet technology you couldn't do that with a dot matrix printer without putting one hand on the telephone and the other one in your ear."
The quiet technology Adam mentioned is making dot matrix printers competitive with the serene laser printers that operate at 43 decibels. When the new dot matrix printers work at 43 decibels, they're quieter than the dripping tap that splashes through the night at 45 decibels.
The new sound levels are accomplished by reworking the parts of the printer that cause the noise. Some manufacturers stagger pin firing to reduce noise. Citizen has redesigned the platen, or roller, to reduce impact noise. The company has also adjusted the carriage and paper feed motors in order to keep your office peaceful. Citizen keeps noise inside its printers through several foam and rubber insulation devices that also cut down on vibration. (If you think vibration isn't a major issue, try setting up an old dot matrix printer on a flimsy card table and watch the show.)
Panasonic's Quiet Series of printers also use noise-reduction techniques.
Another common knock against dot matrix printing is that the documents are of a quality suitable only for passing around the office. It was commonly felt that if you wanted to produce letters or reports for clients, you'd better call in a laser printer. But with new dot matrix developments, this print quality accusation is becoming like most stereotypes--largely untrue.
"Let me put it this way," Adam says, "with the film ribbon, our new 24-wire [pin] printers that we have, I've gone to a couple of people and you've got to get a microscope out and a magnifying glass to really check that it's different from laser quality."
Adam rates print quality on a scale of 1 to 100, with a laser printer having a quality of 100. He says that the new dot matrix printers can produce print at a quality of 90 to 95. With a cloth ribbon in the dot matrix printer, Adam says, print quality may be a little fuzzy. But when using a film ribbon, you'll get the 90-to 95-range quality.
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Even with the rising quality of dot matrix printers, they're probably still no match for laser printers. Adam says the main issue is what you are willing to trade in terms of price for quality.
"There are always tradeoffs," he says. "Do you want to pay $1,000 or $250? Do you want to pay 3 cents a page every time you do it or do you want to pay 8/10 of a cent a page? At every particular price level, there are certain performance capabilities. For the beginner that wants . . . a printer that can do it all, a dot matrix is a good way to get started."
With better resolution and color capabilities, dot matrix printers are now suitable for producing graphics and reports. Bringing a dot matrix up to color capability is a simple task with a cost of around $50. Once your printer is color-equipped, you don't have to worry about removing anything when you want to print in just black and white. The color capability is controlled through software.
A printer that uses hammers and a ribbon to form images out of dots. It is widely used to print multipart forms and address labels. Also known as a "serial dot matrix printer," the tractor and sprocket mechanism in these devices handles thicker media better than laser and inkjet printers.
Hammers Hit the Ribbon
The dot matrix printer uses one or two columns of dot hammers that are moved across the paper. The hammers hit the ribbon into the paper, which causes the ink to be deposited. The more hammers, the higher the resolution. For example, 9-pin heads produce draft quality text, while 24-pin heads produce typewriter quality output. Speeds range from 200 to 400 cps, which is about 90 to 180 lpm. See line matrix printer.
Dot Matrix Mechanism
Dot matrix printers print columns of dots in a serial fashion. The more dot hammers (pins), the better looking the printed results.
Dot Matrix Printer
Dot matrix printers fitted with a tractor feed are commonly used for printing continuous multipart forms and mailing labels. The tractor feed contains a sprocket that grabs the perforated holes at both sides of the form and pulls it through uniformly.
