Laser printer work with photosensitive drums. These drums are connect to a laser which reproduces the image to print it on the drum. The photosensitive drum (s) are electrostatic and attract the ink present in the form of an extremely fine powder by “drawing” the pattern that will be print. The ink is fix to the sheet by heating and compressing the ink sheet in a thermal oven.
The principle of laser printing is as follows:
1. The paper is positively charge with electricity by an ionizer
2. The laser positively electrifies the drum at selecte points
3. The powder ink is negatively electrified
4. The ink is deposite on the positively charge areas of the drum
5 . The drum performs a rotary movement and deposits the ink on the surface to be print
6. A heating device instantly fixes the ink on the surface to be print
Laser printers use two different printing systems depending on the model:
This system requires four printing sequences (“passes”) for a document: each primary color plus black.
This printing method only needs one pass to deposit the material, thanks to the arrangement of the color toners in parallel. Laser printing is therefore faster but more expensive because the mechanism is more complex than in the carousel.
Technical characteristics of laser printing:
Printhead (Laser Lamp)
It consists of a laser which writes the page to be print on a drum. The laser beam is deliver using laser diodes.
Drum (or Photo-conductor)
This photosensitive roller is the most important component of the laser printer. Indeed it is on this support that the laser beam draws the page to be print. It is generally composed of an aluminum cylinder cover with a photosensitive semiconductor (usually silicon) layer as well as various protective layers. It is an electrical device that can be electrically charge but loses its charge as soon as its surface is illuminate with a light source.
It is use to direct the laser beam onto the photosensitive drum.
Pilot Unit (RIP)
It is the processor of the printer. It converts the digital data (0 and 1) receive from the computer into pulses intend to control the laser.
The laser is prefer for printing a large volume of monochrome pages due to its high printing speed and low cost per page.
Inkjet is a non-contact printing process in which very small drops of liquid ink are project by nozzles using electrical intensity and forming dots. It is this concentration of dots that forms characters. Printing is therefore done line by line and not sheet by sheet as is the case with the laser, which is why this printing mode is a little slower than the previous one.
Inkjet printing is done using two techniques:
• CIJ (Continous inkjet): continuous inkjet
• DOD (Drop on Demand): drop on demand.
This is the simplest process. The continuous inkjet (CIJ) is a sub-method of VideoJet Inkjet Printer consists of the formation of regular drops in volume and frequency. They are charge and oriented according to the pattern to be generate and can be divert into a receptacle if they are not desire thanks to an electrostatic field. This will then allow the printhead to be re-supplly.
Drop on demand
The drop-on-demand process is by far the more develop of the two. Drop On Demand (DOD) is generate whenever it is desire.
With this method, the pressure in the ink tank is not constant but applied when a character needs to be form.
Pulse technology is the basis of inkjet printers use in office automation, which is why inkjet is the most common technology in office automation or SOHO (Small Office – Home Office).
It guarantees good print quality but is slower than a continuous inkjet.
Three main ink ejection methods can be consider for this technology:
The piezoelectric process
It is the most develop of the four. The ink tank is in contact with a piezoelectric crystal which will convert the electrical impulses into mechanical force. It is the induce overpressure due to the crystal which allows the droplet to be expel.
The thermal or bubble jet process
It works on the same principle. By heating the ink, it causes local vaporization of it and therefore an overpressure to eject a drop due to this imbalance.
It is also a piezoelectric process but here the ink is solid. It must heat in order to be ejectable. In contact with the media, the ink solidifies and then gives a very good print quality. However, the ink being in relief, it ages badly.
The difference between continuous and on-demand inkjet is that in the CIJ ink is constantly flowing through the printer, from the ink delivery system to the printhead, before being release. return to the ink delivery system. In DOD technology, ink is only disperse when the printer is running.
Inkjet printing is the prefer option whenever you want high quality color rendering that will last over time.
The PageWide technology develop by HP is a revolutionary new process based on inkjet. The secret is in a print bar that prints the full width of the page in one pass. This is made possible by 42,240 tiny nozzles on a stationary printhead that target ink spray onto a moving sheet of paper.
In fact, it is no longer the print head that moves to print but the page. With paper mobility and printhead immobilization, HP PageWide printers print documents at laser speed and have an ultra-fast first page out time.
This diagram shows the paper moving (in green) within the PageWide MFPs.
In addition, these machines are equip with high-capacity consumables, which makes them the cheapest technology with a lower cost per page than all the others.
The main design elements of these machines guarantee impeccable print quality:
• 42,240 nozzles spread over a page width projecting ink drops of identical weight, speed and trajectory.
• 10,560 nozzles are dedicate to each of the four colors. These nozzles sit on top of each other, resulting in a native resolution of 1,200 nozzles per inch.
• HP pigment inks deliver control ink-paper interactions: high black and color saturation, crisp, dark text, and fast drying.
• Precise control of paper movement enables extremely reliable print quality and operation.