Print Technologies | CompTIA A+ 220-1001 | 3.11

In this video you will learn about various print technologies such as: laser printers, inkjet printers, thermal printers, impact printers, virtual printers, & 3D printers.

Laser Printers

Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a “drum” to define a differentially charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated in order to permanently fuse the text, imagery, or both, to the paper.

Typical Laser Printer

A laser printer’s major components are:

  • Imaging drum:  Applies the page image to the transfer belt or roller; frequently combined with the toner supply in a toner cartridge.
  • Developer:  Pulls toner from the toner supply and sends it to the imaging drum.
  • Fuser assembly:  Fuses the page image to the paper.
  • Transfer belt (transfer roller):  Transfers the page image from the drum to the page.
  • Pickup rollers:  Picks up paper.
  • Paper separation pad (separate pad):  Enables pickup rollers to pick up only one sheet of paper at a time.
  • Duplexing assembly (optional):  Switches paper from the front to the back side so that the printer can print on both sides of the paper.
Laser Printer Components

Laser Imaging Process

The 7-step laser printing process:

  1. Processing:  The document to be printed is encoded in a page description language such as PostScript, Printer Command Language (PCL), or Open XML Paper Specification (OpenXPS).  The raster image processor (RIP) converts the page description into a bitmap which is stored in the printer’s laser memory.  Each horizontal strip of dots across the page is known as a raster line or scan line.
  2. Charging:  In older printers, a corona wire positioned parallel to the drum or, in more recent printers, a primary charge roller, projects an electrostatic charge onto the photoreceptor (photoconductor unit), a revolving photosensitive drum or belt, which is capable of holding an electrostatic charge on its surface while it is in the dark.
  3. Exposing:  A laser printer uses a laser because lasers are able to form highly focused, precise, and intense beams of light, especially over the short distances inside a printer.  The laser is aimed at a rotating polygonal mirror which directs the light beam through a system of lenses and mirrors onto the photoreceptor drum, writing pixels at rates up to 65 million times per second.  The drum continues to rotate during the sweep, and the angle of sweep is canted very slightly to compensate for this motion.  The stream of rasterized data held in the printer’s memory rapidly turns the laser on and off as it sweeps.  The laser beam neutralizes the charge on the surface of the drum, leaving a static electric negative image on the drum’s surface which will repel the negatively charged toner particles.  The areas on the drum which were struck by the laser, however, momentarily have no charge, and the toner being passed against the drum by the toner-coated developer roll in the next step from the roll’s rubber surface to the charged portions of the surface of the drum.
  4. Developing:  As the drums rotate, toner is continuously applied in a 15-micron-thick layer of the developer roll.  The surface of the photoreceptor with the latent image is exposed to the toner-covered developer roll.  Toner consists of fine particles of dry plastic powder mixed with carbon black or coloring agents.  The toner particles are given a negative charge inside the toner cartridge, and as they emerge onto the developer drum they are electrostatically attracted to the photoreceptor’s latent image (the areas on the surface of the drum which had been struck by the laser).  Because negative charges repel each other, the negatively charged toner particles will not adhere to the drum where the negative charge (imparted previously by the charge roller) remains.
  5. Transferring:  A sheet of paper is then rolled under the photoreceptor drum, which has been coated with a pattern of toner particles in the exact places where the laser struck it moments before.  The toner particles have a very weak attraction to both the drum and the paper, but the bond to the drum is weaker and the particles transfer once again, this time from the drum’s surface to the paper’s surface.  Some machines also use a positively charged “transfer roll” on the backside of the paper to help pull the negatively charged toner from the photoreceptor drum to the paper.
  6. Fusing:  The paper passes through rollers in the fuser assembly, where temperatures up to 427 degrees Celsius (801 degrees Fahrenheit) and pressure are used to permanently bond the toner to the paper.  One roller is usually a hollow tube (heat roller) and the other is a rubber backed roller (pressure roller).  A radiant heat lamp is suspended in the center of the hollow tube, and its infrared energy uniformly heats the roller from the inside.  For proper bonding of the toner, the fuser roller must be uniformly hot.
  7. Cleaning:  As the drum completes a revolution, it is exposed to an electrically neutral soft plastic blade that cleans any remaining toner from the photoreceptor drum and deposits it into a waste reservoir.  A charge roller then re-establishes a uniform negative charge on the surface of the now clean drum, readying it to be struck again by the laser.

Laser Maintenance

The major elements when it comes to laser printer maintenance (make sure the printer is turned off & disconnected from any power sources):

  1. Replacing Toner Cartridge:  When the toner runs low, replace the toner cartridge and the imaging drum if the laser printer’s toner cartridge is included with the imaging drum.
  2. Applying Maintenance Kits:  Printers have a lot of moving parts that can wear down over time and will eventually need to be replaced.  These components often include fuser assemblies, air filters, transfer rollers, pickup rollers, other types of rollers, and separation pads.  Printer manufacturers will supply you with a maintenance kit to allow for you to swap out or replace parts once a predetermined print page count has been reached.
  3. Calibration:  Laser printers should be calibrated if print quality declines.  The printer calibration process on a laser printer adjusts image density settings to make up for changes caused by environmental differences or aging print cartridges.  Some laser printers perform automatic calibration, but you can also force the printer to perform calibration on an as-needed basis.  See the instruction manual for your printer for details.
  4. Cleaning:  Laser printers use very fine-grained powdered toner.  You can use a vacuum cleaner that is designed to clean up laser printer toner due to the particles getting everywhere inside & outside of the printer.  The best advice is to follow the cleaning instructions outlined by the manufacturer of the laser printer as it relates to different parts & components of the printer.

Inkjet Printers

Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers are the most commonly used type of printer, and range from small inexpensive consumer models to expensive professional machines. Inkjet printers are the most popular type of printer in small office/home office (SOHO) use. Their print quality can rival that of laser printers, and virtually all inkjet printers in use today are able to print both color and black text and photographs.

Typical Inkjet Printer

Inkjet Components

The major components of a standard inkjet printer:

  • Ink cartridge (some inkjet printers use external ink tanks)
  • Print head
  • Roller
  • Paper feeder
  • Duplexing assembly
  • Carriage
  • Belt
Standard Inkjet Printer Components

Inkjet Maintenance

The major elements of maintaining an inkjet printer:

  • Replace the ink cartridge(s): The printing preference or printer properties dialog for your operating system will provide information to let you know when it’s time change out ink cartridges.
  • Calibration: Most inkjet printers will require some type of printer calibration, especially as it relates to print head alignment. This process involves printing one or more sheets of paper to check to see if the printer prints straight lines. This process can be done automatically or manually.
  • Nozzle check: If the printer has been idle for a while, perform a nozzle check. A nozzle check (pattern check) will print a pattern that uses all of the nozzles from all of the print heads to display a pattern’s correct appearance. Use the printout to compare against the pattern image displayed onscreen to check for gaps or missing colors. Run the nozzle check again until the pattern matches. Be mindful that nozzle checks require the use of ink.
  • Clean print heads
  • Clearing paper jams

Note that some printers run automatic nozzle cleaning or calibration routines when you change ink cartridges.

Thermal Printers

Thermal printing is a digital printing process which produces a printed image by selectively heating thermal paper when the paper passes over the thermal print head. The coating turns black in the areas where it is heated, producing an image. Two-color direct thermal printers can print both black and an additional color (often red) by applying heat at two different temperatures. The most common use for thermal printing can be found at cashier machines when printing out receipts (also known as point-of-sale, POS).

Typical Thermal Printing

Thermal Feed Assembly & Heating Element

Features of a standard thermal printer

  • Feed Assembly:  Pulls paper from a roll wound around a center plastic spool or spindle.
  • Heating Element:  Used to heat thermal paper or ribbons to make an image.

Special Thermal Paper

Thermal paper (sometimes referred to as an audit roll) is a special fine paper that is coated with a material formulated to change color when exposed to heat. It is used in thermal printers, particularly in inexpensive or lightweight devices such as adding machines, cash registers, and credit card terminals. The surface of the paper is coated with a solid-state mixture of dye and a suitable matrix. When the matrix is heated above its melting point, the dye reacts with the acid, shifts to its colored form, and the changed form is then conserved in a metastable state when the matrix solidifies back quickly enough.

Thermal Paper

Thermal Maintenance

The major elements of maintaining a thermal printer:

  • Replace paper when paper runs out
  • Clean heating element: Many vendors recommend cleaning the print head after each roll of thermal transfer ribbon. You can also use isopropyl alcohol to clean print heads.
  • Remove debris: Use cleaning materials recommended by printer manufacturer to remove debris such as torn paper, solid ink flakes, & label coatings that can build up on rollers and the print head.

Impact Printers

Impact printers create an image by using some mechanism to physically press an inked ribbon against the page, causing the ink to be deposited on the page in the shape desired. These printers are typically loud, but remain in use today in mostly industrial and point-of-sale applications because of their unique ability to function with multipart forms. Dot-matrix printers (prints characters from dots placed on a page) are the most common form of impact printers.

Typical Impact Printer

Basic elements of impact printing:

  • Print head
  • Ribbon
  • Tractor feed
  • Impact paper
Dot Matrix Impact Print Head & Ribbon

Impact Printer Paper Types

Impact printers use plain uncoated paper or labels in various widths and sizes.  These printers typically use a tractor feed mechanism to pull or push the paper past the print head.  Tractor-fed printer paper and labels have fixed or removable sprocket holes on both sides of the paper.  This type of media is often called “impact”, “dot-matrix”, “continuous feed”, or “pin-feed” paper or labels.

Impact Printer Maintenance

The major elements of maintaining an impact printer:

  • Replace the ribbon:  The ribbon on an impact printer lubricates the pins in the print head & protects the print head from impact damage.
  • Replace the print head:  If damage to one or pins is detected, replace the print head.  Damaged pins could snag the ribbon or if the pin(s) break, it could leave gaps in the characters being printed out.
  • Replace the paper:  Check for problems with torn sprocket holes, separated tear-offs, and damaged sheets.  Tear off any problematic pages & use only good paper from the paper stack.  Also adjust the tracker feeders as necessary to ensure the printer is properly pulling and pushing paper.

Virtual Printers

In computing a virtual printer is a simulated device whose user interface resembles that of a printer driver, but it is not connected with a physical printer. The virtual printer is used to create a file instead of a printout.

Virtual Printer

There are three major categories of virtual printers:

  • Print to file: Used to create a file that can be copied to a specific printer for output.
  • Print to PDF or XPS (Microsoft XPS): Used to save files that cannot be modified but still need to be easily shared and printed.
  • Print to image: Designed to convert documents directly into common bitmap graphic formats such as TIFF, JPEG, BMP, etc. Some of these apps can also create PDF files.

3D Printers

3D printing (additive manufacturing) is the construction of a three-dimensional object from a CAD model or a digital 3D model. The term “3D printing” can refer to a variety of processes in which material is deposited, joined or solidified under computer control to create a three-dimensional object, with a material being added together (such as liquid molecules or powder grains being fused together), typically layer by layer.

3D Printer

Fused deposition modeling (FDM) is the main 3D printing process most people are familiar with. The most common material is a strand of plastic filament that is fed from a spool to a moving printer head.  The printer head heats the plastic and thinly layers it on the printing platform in cross sections that eventually build up into the 3D object that has been designed on the computer.  This process is carried out on a 3D printer using these four components:

  • Filament:  This is the plastic material that is fed from a spool, though many different materials can be used.  The filament is the “ink” of an FDM printer and is available in various colors.
  • Extruder:  Receives the plastic filament and melts it.
  • Nozzle:  The nozzle is a small spray hole that emits the melted filament.
  • Bed:  The bed is the platform on which the object is created.

Maintaining 3D Printers

Best practices for maintaining a 3D printer:

  • Ensure you have heat resistance lubricants or they may melt and become part of the printed object.
  • Use different brushes to clean different parts of the printer. Example: stiff brass brushes are good for cleaning the outside of nozzles.
  • Clean the filament in between print jobs & make sure it is at the correct temperature.