Printers

General notes about printers.

• A single physical “print device” can be represented in a Windows operating system by multiple “printers,” that is, by multiple logical devices listed in the Windows Printers and Faxes window. These logical printers can have different drivers. I personally have an example of this with my inkjet printer.
• A “network printer” is a printer with its own NIC (or wireless NIC), and which doesn’t need to have a parallel, or usb connection, to a specific printer.
• In this situation the NIC in the printer connects directly to the network with an RJ-45 plug, or the wireless NIC makes wireless connectivity. It does not need an LPT, serial, or usb connection to any computer, in order for any computer in the peer to peer or client-server network to access the printer.
• It is itself a network node, rather than being a peripheral device attached to a network node consisting of a computer.
• Any non-network printer is perfectly capable of being accessed over a network. It just needs to be attached to a specific computer using an LPT parallel cable, or using a serial or usb connection, or a Bluetooth (wireless) connection. The computer is the network node, rather than the printer itself. The NIC is in the computer, rather than in the printer. The computer must be On and connected to the network, for the other computers in the network, either a peer to peer or client server network, to use the printer.
• There might be a question about dot matrix printers. Know what one is.

Laser Printers

• The standard terminology is CCWDTF. Clean, Condition, Write, Develop, Transfer, Fuse. Clean, condition, write, and develop to the drum, one raster line at a time. Then repeat, circle. You have to start the description of this circular process somewhere: generally it is at clean.
• I think it may elucidate the process more clearly if, instead, or in addition, one says CCDTTF, Clean, Charge, Discharge, Tranfer 1, Transfer 2, Fuse. Clean the drum, Charge the drum, Discharge parts of the drum representing text or graphics, Transfer toner from toner bin to drum, Transfer toner from drum to paper, Fuse toner to paper.
• Do C, C, D, T1 to the drum, and T2, F to the paper, line of dots by line of dots.
• Clean the photoreceptive drum. Yup, clean it.
• Condition the photoreceptive drum — charge it to -600v.
• Write to the photoreceptive drum — discharge those areas of the photoreceptive drum corresponding to text or graphics and corresponding to where negatively charged toner is will need to be attracted to the drum, in preparation for the next step, the Develop step, alternatively called Transfer 1 step. The ultimate source of data for each line consisting of a sequence of dot or no-dot, called a raster line or scan line, to write to the drum, is a data file. The data file gets modified by programs on the computer controlling how to convert the data in the file into data that is appropriate for the particular printer, and this data is modified by a program in the printer called a Raster Image Processor. As the drum turns, the mirror moves, and the laser turns on or off — controlling where the raster line contacts the drum, and the sequence of dots (discharged spots) or no-dots in each line.
• Develop or Transfer 1 means actually transfer the toner from a toner bin to the discharged areas of the photoreceptive drum. A pickup unit or developer drum facilitates the process. It picks up toner from the bin and moves it to the photoreceptive drum.
• Tranfer or Transfer 2 means tranfer a raster line of the toner that is on the drum, to the paper. A transfer corona facilitates the process.
• Fuse means heat the paper so that the toner sticks to it.
• So, yea, Clean drum, Charge drum, Discharge spots on drum, Transfer toner to Drum, Transfer toner to Paper, Fuse toner to paper. Clean, Charge, Discharge, Transfer, Transfer, Fuse. CCDTTF. Oh yea — and go back to the beginning. The 6 things happens in rapid sequence during which time the drum makes only a fraction of a revolution, and happen over and over again. After the roller makes several revolutions, it has transferred a whole page worth of toner to a sheet of paper.
• Maybe you should just memorize the above steps, and be ready for hearing them detailed below.
• Here is a video with an animation showing what is going on in regard to transfering toner to the photoreceptive drum, and then to paper.
• There are 3 "corona" wires. During conditioning, or charging, a charge corona gives the photosensitive drum a negative charge. During transfer, or transfer 2, a transfer corona transfers toner from the photoreceptive drum, to paper. And after the toner is transferred to paper, the paper is discharged by a discharge corona, also called a detac corona. It prevents paper from sticking to the photoreceptive drum. Not sure if it happens before or after the fuser process.
• A pickup unit is a mechanical device that brings paper to where it can be squeezed between the photoreceptive drum and transfer corona. Consists of rollers. An electric motor turns them. But before squeezing the paper between the photoreceptive drum and the transfer corona, to tranfer toner to the paper, you must first get toner to become developed onto the photoreceptive drum.
• Unit has 3 cylinders, alternatively called rollers, or drums. (1) A photoreceptive drum which is charged by the primary corona, that is, the charge corona, and then written to by the laser; (2) a developing cylinder which picks up toner from toner cartridge and brings it to the photoreceptive drum, where it either sticks (to the "written" areas, which are less negative) or gets repelled (from the unwritten areas, which are the most negative); and (3) a fusing roller which uses heat to fuse toner to paper. In short, the (1) developing cylinder is what is used to get the toner onto the (2) photoreceptive drum, from which it is soon transferred to paper by transfer corona, after which it is firmly fused to the paper by the (3) fusing roller.
• The photoreceptive drum gets charged to about -600 vdc by the primary corona. Then laser then “writes” to the photoreceptive, discharging it to about -100 vdc wherever the "writing" is. This works because light makes it hard for the material of the drum to hold a charge.
• Typically, a cartridge contains the photoreceptive drum as well as toner. It often also contains the developing cylinder. The tranfer corona and fuser are both usually outside of the cartridge.
• During development, toner acquires a -600v neg charge from the -600 volt developing roller (which has a magnet in it), as it is pulled up by the developing roller during the developing phase. Note that the photoreceptive drum got charged to -600v by the charge corona, but the toner acquired its equal -600v charge from the developing cylinder.
• Key point: because of the developing cylinder, the toner comes to have the same charge as the unwritten parts of the drum, and thus is (relatively) repelled from unwritten areas, and attracted to written areas.
• After development, that is, after the developing cylinder has transferred toner to the photoreceptive drum, the photoreceptive drum will have a -600v charge both in "background" areas, where it was charged by the primary corona, and, as well, in "written" areas, where -600v toner has become stuck to the drum.
• The process of darkening or lightening the image, and increasing or decreasing contrast, happens during development stage, and is complicated. Making toner -500 instead of -600  should, acc to my logic, cause less repulsion from background area less attraction to written area. Maybe even slight attraction to background but also less attraction to written area. Decrease in contrast. Making it maybe -700 will cause some attraction to background area and more attraction to written area. Darker image spreading into background more.
• With development completed, we are now ready to transfer the toner from the photoreceptive drum to paper.
• During tranfer stage, the tranfer roller, or the transfer corona, imparts a uniform +600 v charge to the paper, or near to the paper. The positively charged paper pulls all the negatively charged toner away from the (uniformly negatively charged) drum, and to the paper. Dere's your image. It gets fused by the fusing roller.
• After that the drum needs to be cleaned by a scraper and also erased by a fluorescent lamp. Also, the primary corona will supply an AC bias, to remove any remaining residual charges left by the previous image. This is the end of the “cleaning” process, before the same primary corona supplies conditining via a DC bias (the -600 vdc)
• Once raster image generation is complete all steps of the printing process can occur one after the other in rapid succession. This permits the use of a very small and compact unit. The photoreceptor drum is charged, rotates a few degrees and is scanned, written to by laser, rotates a few more degrees and is developed (attracts toner to itself) from the developing roller, and so forth. For an entire page to be completed, the photoreceptive drum and developer drum must rotate several times.
• Laser printers generally use this “black-write” process, which we just described, where the laser marks the black areas wher toner will be attracted to and black print will  be printed. With a “white-write” process, the laser marks areas where toner is not attracted, and where the page will not have black print. First drum is charged. Then white area is written to by laser. Then uncharged toner is attracted to areas where laser didn’t discharge drum and drum retains its charge. Photocopiers generally use a white-write. Of course they don't use a laser to write to the photoreceptive drum, with digital information, but instead use an analog process, using light that has been reflected off the paper to be copied.
• A color laser printer is very much the same except as a monochrome laser printer except that the process is repeated each time for each of the primary colors, cyan, magenta, yellow, and black. In lower cost laser printers, the process is repeated sequentially, using a single laser diode, and they perform color printing much slower than they perform monochrome printing, about 1/3 the speed. More expensive laser printers repeat the process simultaneously, using 4 laser diodes, and can do color printing almost as fast as monochrome printing.
• LED (Light Emitting Diode) printers are just like laser printers, except instead of using a laser diode and a mechanism with an electric motor and a series of mirrors and lenses, to move a single laser beam (or 4 laser beams in color laser printers with simultaneous lasers) across the photoreceptive drum, a stationary "array" of numerous LED's and a single lens is used, near to the photoreceptive drum. The LED's do not need to be moved; they use much less electricity than a laser printer. They use only about 1/4 to 1/3 as much. They are sometimes called "laser class" printers to distinguish them from true laser printers.
• Newer low-cost and intermediate-cost LED printers have just as many dots per inch and just as high quality of printout, as low-cost and intermediate-cost laser printers. For very finely detailed graphics and tiny print, a high-end laser printer may be able to produce a slightly better image than a LED printer, with more dots per inch, and better resolution. However LED printers are more than adequate for all but the most demanding applications.
• A monochrome LED printer that prints at 600 dpi has 600 LED's per inch! For monochrome, that comes to 4800 LED's per page, over an 8-inch wide page. Even at such high numbers of LED's, the writing mechanism in a LED printer is cheaper than that in a laser printer. Color LED printers have 4 times as many LED's.
• Another cost-saving advantage of LED printers over laser printers is that color LED printers can produce color output almost as fast as monochrome output, without the added expense of 3 extra laser diodes and their associated electronics. Each of the 4 colors can be written to the photoreceptive drum simultaneously using 4 sets of LED's. Multiplying the number of LED's by 4 does not increase the cost as much as multiplying the number of laser diodes by 4.
• LED arrays are slightly smaller in volume than laser mechanisms, and LED printers can be made slightly smaller in overall volume and desktop area requirements, than laser printers. They tend to be quieter, too.
• Laser class printers generally have 6 subsystems:
• Power supply, logic and control circuit, laser unit, paper transport mechanism, toner-drum-developer mechanism, fuser mechanism.
• Troubleshooting notes: If the primary corona does not apply a negative charge to drum, toner will not be repelled from it anywhere, and will stick to drum not only where laser positivizes certain areas, but also all over, and page will tend to be all black.
• When a toner cartridge becomes depleted it may print a black line along the side of each page.
• Dirty tranfer corona? Sloppy job of toner tranfer. Faded. Indistinct.
• Non-working fuser? Ink isn’t well attached to paper, smears.
• Lack of memory? Areas of text or graphic missing. Usually it is the more complex graphics that are missing.
• Scratch on drum? Vertical line on paper.
• Forgetting to remove tape from new toner cartridge will result in blank pages being printed.

InkJet printers

• Inkjet works by piezoelectric vibrations or heating and vaporizing and expanding ink, thus forcing it out of a nozzle.
• Cleaning ink nozzle is accomplished by running printer utility for the printer, or powering printer off-on.
• If inkjet printhead needs alignment, printout will have jagged lines.