Printers And Printer Types Computer Science Essay Example

of paper, toner, and occasional drum replacement, along with replacing other consumables like the fuser assembly and transfer assembly. Frequently, printers equipped with pliable plastic drums may incur a significantly high cost of ownership that only becomes evident when the drum needs replacement.

A duplexing printer, which prints on both sides of the paper, can reduce paper costs and filing volumes. While duplexers were once limited to high-end printers, they are now commonly found on mid-range office printers. However, not all printers have the capacity to accommodate a duplexing unit. It is important to note that duplexing may result in a slower page-printing speed due to the longer paper path.

Most inkjet printers and dot-matrix printers function differently than laser printers. They imprint data directly in a slow, intermittent manner, causing pauses when waiting for more data. Unlike them, laser printers require a rapid and continuous output of a large amount of data to the printing device. Stopping the mechanism to wait for more data would result in visible gaps or misalignment of dots on the printed page.

The image data is usually stored in a computer's memory before being printed by a laser printer. This means that laser printers have typically been limited to printing on smaller paper sizes, like letter or A4, because they don't have enough memory to store larger images. As a result, printing continuous banners that span a two-meter-long sheet of paper is not possible on most laser printers.

The laser printer was invented at Xerox in 1969 by researcher Gary Starkweather, who had an improved printer working by 1971 and incorporated into a fully functional networked printer system by about a year

later. The prototype was built by modifying an existing xerographic. Starkweather disabled the imaging system and created a spinning drum with 8 mirrored sides, with a laser focused on the drum. Light from the laser would bounce off the spinning drum, sweeping across the page as it traveled through the copier. The hardware was completed in just a week or two, but the computer interface and software took almost 3 months to complete.

The IBMA model 3800A, which was the first commercial laser printer, was introduced in 1975. It was primarily used for high-volume printing of documents like invoices and mailing labels. Although it is commonly described as "taking up a whole room," implying its outdatedness compared to modern laser printers, the 3800A was actually intended for a different function. Despite its size, many 3800s are still actively utilized today.[citation needed]

The first laser printer designed for office use was the Xerox Star 8010, released in 1981. Although it was innovative, the Star had a high price tag of $17,000, and only a limited number of businesses and institutions purchased it. As personal computers became more common, the first laser printer for the mass market was the HP LaserJet 8ppm, which was released in 1984. This printer used a Canon engine controlled by HP software. Brother Industries, IBM, and other companies quickly followed HP's lead and introduced their own laser printers. The initial models had large photosensitive drums that were larger than the paper length. However, as faster-recovery coatings were developed, the drums could make multiple passes on the paper and thus be smaller in diameter.

The price of laser printers has significantly decreased over the years, like

most electronic devices. In 1984, the HP LaserJet was sold for $3500, had difficulties with low resolution graphics, and weighed 71 pounds (32A kg). Monochrome laser printers at the lower end of the market can now be purchased for less than $75 as of 2008. These printers usually do not have their own processing capabilities and instead depend on the connected computer to create a raster image (see Winprinter). However, they still outperform the LaserJet Classic in almost all scenarios.

Each strip of dots across the page is called a raster line or scan line. The creation of the printable image is handled by a device called a Raster Image Processor (RIP), which is usually integrated into the laser printer itself. The source material can be encoded in various page description languages such as Adobe PostScript (PS), HPA Printer Command Language (PCL), Microsoft XML Page Specification (XPS), or plain text. The RIP utilizes the page description language to generate a bitmap representation of the final page in the raster memory. Once the entire page has been rendered in the raster memory, the printer is prepared to send the stream of dots to the paper as a continuous flow.

The original Hewlett Packard LaserJet had only 128 kilobytes of memory. It was primarily used for printing text and did not have the capabilities of modern graphical printers. The page character information was stored in a small number of kilobytes, and the dot patterns for each raster scan line were obtained from font bitmap tables stored in Read Only Memory (ROM). Additional fonts could be added through ROM cartridges that were inserted into expansion slots.

For a complete graphical output

using a page description language, a minimum memory capacity of 1 megabyte is needed. This memory is required to store an entire monochrome letter/A4 sized page consisting of dots at 300 dpi resolution. At this resolution, there are 90,000 dots per square inch or 300 dots per linear inch.

Typically, an 8.5 x 11 sheet of paper has margins of 0.25 inches, which reduces the printable area to 8.0 x 10.5 inches or 84 square inches. Multiplying this area by the density of 90,000 dots per square inch results in a total of 7,560,000 dots necessary for the whole page.

In contrast, 1 megabyte is equal to 1,048,576 bytes or 8,388,608 bits. This capacity is just enough to accommodate the entire page at a resolution of 300 dpi and leaves approximately extra space of about100 kilobytes that can be utilized by the raster image processor.

Each of the four CYMKA toner layers in a colour printer is saved as a separate bitmap. Typically, all four layers are preprocessed before printing starts, requiring at least 4 megabytes for a full-colour letter-size page at 300 dpi.

The memory requirements for printing increase with the square of the dpi. For monochrome printing at 600 dpi, a minimum of 4 megabytes is needed, whereas for color printing at the same resolution, it requires 16 megabytes. However, certain printers have additional features like variable size dots and interstitial dots, which can significantly increase the memory needed beyond the minimums mentioned earlier.

If printers are capable of printing tabloid and larger sizes, they may include slots for memory expansion. Insufficient memory can result in disabled features, such as limited monochrome printing at tabloid size instead of

color printing at letter size. Increasing the memory capacity through additional purchases enables color printing at the larger size.

Older printers utilize a corona wire or a primary charge roller to project an electrostatic charge onto the photoreceptor (also known as the photoconductor unit). This photoreceptor is a revolving photosensitive drum or belt that can retain an electrostatic charge on its surface when not exposed to light.

An A ACA bias is used on the primary charge roller to eliminate any remaining charges from previous images. It also applies a DCA bias on the drum surface to achieve a consistent negative potential. The DC bias affects the desired print density. [4]

The photosensitive drum coating is described in numerous patents as a silicon sandwich with multiple layers. One version of this coating includes an amorphous silicon layer that receives light, a boron nitride layer that prevents charge leakage, and a surface layer made of doped silicon. This doped silicon can contain oxygen or nitrogen and has a similar appearance and properties to machined silicon nitride. This coating creates a photosensitive drum with minimal leakage and resistance to scuffing.[citation needed]

The laser beam is directed towards a rotating polygonal mirror which then directs it through a system of mirrors and lenses onto the photoreceptor. The sweep of the beam across the photoreceptor compensates for the motion of the rotating cylinder. To create dots on the cylinder, the laser is turned on and off using rasterized data stored in memory. Laser printers utilize lasers because they can generate a narrow beam capable of traveling long distances. By reversing the charge on black parts of an image, the laser beam creates

a negative image on the surface of the photoreceptor, which is used to apply toner particles.

The laser sweeping process is synchronized at the end of each sweep cycle using a beam detect (BD) sensor.

The latent image surface is treated with toner, which consists of dry plastic particles mixed with carbon black or colorants. The toner particles are negatively charged and are attracted to the photoreceptor's latent image, specifically the areas exposed to the laser. Due to the repulsion between like charges, the negatively charged toner does not come into contact with the drum where the negative charge remains.

The darkness of the printed image is controlled by the voltage charge applied to the supply toner. After the charged toner reaches the surface of the drum, its negative charge repels more toner from jumping to the drum. If the voltage is low, a thin coat of toner stops more toner transfer. Conversely, if the voltage is high, a thin coating on the drum cannot prevent more toner transfer. In this case, more supply toner continues to jump to the drum until the charges on the drum can repel it. On the darkest settings, the supply toner voltage coats the drum even where its initial charge is still present, resulting in a dark shadow across the entire page.

The image is transferred to the paper by pressing or rolling the photoreceptor. In more advanced machines, a positively charged transfer roller on the back of the paper is used to pull the toner from the photoreceptor to the paper.

The plastic powder is bonded to the paper when it goes through rollers in the fuser assembly, which applies heat (up

to 200 Celsius) and pressure.

One roller is typically a heat roller, which is a hollow tube, while the other is a pressure roller made of rubber. The heat roller contains a suspended radiant heat lamp in its center, emitting infrared energy to evenly heat the roller from within. To ensure the toner adheres properly, it is essential for the fuser roller to maintain a consistent and uniform level of heat.

The fuser, which accounts for approximately 90% of a printer's power usage, can generate so much heat that it may cause damage to other printer components. To prevent this, fans are often employed to ventilate the fuser and dissipate the heat from the printer's interior. One common power-saving feature in copiers and laser printers is to shut off the fuser and allow it to cool down. However, before printing can resume, the fuser needs to reach its normal operating temperature.

Some printers have a thin, flexible metal fuser roller that allows for faster and more frequent heating, ensuring quicker operating temperature. This speeds up printing when the printer is idle and allows for more frequent fuser shutdowns to save power.

If the paper moves at a slower pace through the fuser, it allows for more contact time between the roller and the toner, thus enabling the fuser to function at a lower temperature. This energy-saving design results in smaller and more affordable laser printers having a slower printing speed compared to larger, high-speed printers, where the paper moves faster through a high-temperature fuser with minimal contact time.

After printing, a waste reservoir collects any excess toner from the photoreceptor using an electrically neutral soft plastic blade. Additionally, a discharge

lamp is used to remove the remaining charge from the photoreceptor.

When unexpected events like a paper jam occur, there might be instances where toner is left on the photoreceptor. The toner is already on the photoconductor and ready for application, but the operation fails before it can be implemented. In such cases, it is necessary to wipe off the toner and restart the process.

Waste toner cannot be used again for printing due to potential contamination with dust and paper fibers, which can result in poor print quality and improper toner fusion. However, certain laser printers like Brother and Toshiba models have a patented process to clean and recycle the waste toner.

After the raster image is generated, all steps of the printing process can occur in rapid succession. This allows for the use of a small and compact unit. The photoreceptor is charged, rotates a few degrees, is scanned, rotates a few more degrees, is developed, and so on. The entire process can be finished before the drum completes one revolution.

Various printers have different approaches to implementing these steps. Some printers, known as "laser" printers, use a linear array of light-emitting diodes (LEDs) to create the light on the drum. There are two types of toner used, either wax or plastic, that melt when the paper goes through the fuser assembly. The paper may or may not have an opposite charge. The fuser assembly can be an infrared oven, a heated pressure roller, or a xenon flash lamp on high-speed, expensive printers. When a laser printer is first powered on, it goes through a warm-up process mainly to heat the fuser element. Many printers have a

toner-conservation mode called "Economode" by Hewlett-Packard, which uses approximately half the amount of toner but produces a lighter draft-quality output.