| Laser Printers - Index Printers > Laser > Index |  | Navigation Icons Guide
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| Origins of laser printers - Principle of electrostatic copying or "xerography" developed Chester Carlson in 1938. Laser printer principle invented by Gary Starkweather of Xerox PARC in 1971. |  |
Types -
 | Commercial & industrial high speed press - beating platemaking on short runs of things like books and catalogues. |
| Office workgroup mono and colour printers - sharing information. |
| Personal & home mono and colour printers - entertainment and art |
Merits
| Problems
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Laser Printer Basics - characters made from microscopic pixels at between 300 and 2400 dpi.
Laser Printer Market - predominantly office workgroups and SOHO.
From 1990 onwards the first choice for high-volume general print.
General Principles
Inventors:
Chester Carlson invented in 1937, Battelle promoted, adopted by Haloid which became Xerox. 
Gary Starkweather & team modified a Xerox 9200 adding laser, RIP and Ethernet.
Copiers & Printers - market switch around so that a copier is now a scanner /printer.
Electrophotography Process Overview. Photocoductivity, Electrostatic Attraction.
Drum - photoconductor usually in the form of "OPC", charged to several hundred volts.
Scanning - latent image created by raster scanning with laser light.
Developer - image made visible bya fine powder "toner" that clings to charge.
Toner Transfer - image in toner transfered to paper by pull of another charge.
Fuser - lose toner on top of the paper melted and pressed into paper.
Electronics & RIP - Even a basic page is about 8 million pixels.
Costs - cost of the machinery and cost of toner and paper.
Paper - has to be right for the process - but common office paper works fine.
Toner - powder to be electrostically charged and held, then melted and give strong colour.
Wear - many of the parts wear out, but manufacturers assemble them in cartridges.
Manufacturers - more than 20 manufacturer competing to give the best deal .
OEMs & Engines - Fewer makers of "engines" but different electronics & software.
Cartridges - the real focus for the manufacturer is to sell cartridges, not printers.
Environment -
Lasers & Light Sources - most printers use low power lasers
Raster Scanning - rapidly modulated, sharply focused beam.
Polygon Mirror - multi-faceted mirror sweeps laser beam across page.
LED Printers - 8 inch 210mm bar with about 2,400 LEDs.
LCD Imaging - Used in the Qume crystalprint.
Exotic Imaging -micromirrors.
Porous silicon
Shuttle LED?
Consumables Summary - the greater part of printers are consumables in some way.
Toner - main material used, roughly in proportion to page cover.
Waste-bottle - collects from the drum toner not fully transfered to paper.
OPC - Organic Photoconductor takes up image in static - wears out with use.
Developer - Applies toner to the OPC where there is a static charge.
Fuser - Fixes toner to the paper.
Consumables as a User Puzzle - Early printers had four or five changeable modules.
Maintenance - swapping parts eliminates many faults.
Small cartridges with low content quantity seem more popular than big long lasting versions.
Integrated cartridges - put most or all of the works into one cartridge.
Modern Printers and "affordable" cartridges.
Bulk Consumeables - are used in copiers but rare in printers.
Waste & Recycling.
Photo-Conductor - heart of the design is material that is an insulator in the dark and conducts in light coated onto a drum or belt to act as a temporary image store.
opposite charges attract, like charges repel - printer uses high voltage for strong result.
photo-conductivity - light changes conductivity - quite dramatically in some materials.
Photostatic Materials- selenium, selenium-arsenic, amorphous silicon etc.
OPC materials - Laser printer usually 2 layer OPC - CTL holds charge, CGL discharges it.
handling - materials quite soft and can be scratched or denatured by grease.
sensitivity - loses sensitivity with exposure to light.
linearity - difficult to extract much of a grey scale.
Mechanics:
Drum - aluminium or steel drum gives a stable surface - but a small area.
Belt - much larger surface - but difficult to get accurate positioning.
Charge Mechanism - usually Minus 600 Volts on Drum, opposite charge under paper.
Corotrons - High tension wires in a metal box with an open side. Creates charge field.
Ozone - Corotrons strip oxygen molecules and make ozone.
Rollers - can use much lower voltages and transfer them by contact.
HT voltages - Charges for Drum, Developer and Transfer Station.
Photoconductor Life - limited by oxidation, contamination and exposure.
Amorphous Silicon (aSi) used in Kyocera FS1500 and Canon copiers.
Premature Failure - Scraper blade failure, scratches, overexposure, bad contacts.
Developer & Toner - colourant that can be manipulated electrostatically.
Toner - the "ink" or colourant for paper. Triboelectric, adhesive and maleable properties.
Toner Ingredients - Styrene, acrylic or polyester resin. Microcapsule structures.
Grain Size - less than half pixel diameter. If analog response is wanted, much smaller.
Nanoengineered Powders are used for triboelectric charge and adhesion control.
Melting Point - low melting point gives fast low temperature fusing.
Colourant - main purpose of toner, often a small percentage. Binary or Linear.
Developer - applies the toner in a controlled fashion eflecting electrostatic contours.
Iron Velvet - toner coats onto iron filings, rollers & magnets present toner to OPC.
Resin - electrostatic charge on roller holds the toner ready for transfer to the drum.
Cartridges - putting all the main consumables in a cartridge equires a balance.
Problems with cartridges.-
Toner - runs out but the printer should warn of it. Check the image on a drum.
Developer - uneven or faint print, score marks from damaged ollers.
Cleaner & Waste - Transfer stations don't take everything off the drum.
Eraser Lamps - Row of Red LEDs release the residual charges on the drum.
Scraper Blade - Forces any surplus toner off the drum surface.
Brushes - used on some faster printers - less resistance.
Waste Transport - usually an archimedes screw.
Waste Bottle - Can be a plastic bottle. Integrated cartridges have compartment.
Waste ReUse - Just don't!
Cartridges - purpose of the printer is to put toner on paper, so it consumes quantities of both. Laser printing also tends to use an OPC, Developer and a fuser.
Users should be grateful that most maintenance activities are just a matter of swapping fairly low cost cartridges around.
Integrated cartridges
Economics
Profit
Originals
Oddly, nobody puts paper in a cartridge
Although cartridges look wasteful the real cost of the plastic carcas may not be much greater than that of making the cardboard box it is supplied in.
Health - laser printers contain hazardous parts but cutout switches protect users.
Laser - definitely an eye hazard and theoretically a fire hazard in some printers.
Electrical - high voltages and mains current.
Fire - main hazard from the fuser which has cutouts.
Toner - manufacturers generally say its safe.
Toner Dust - don't use ordinary vacuum cleaners.
Toner Vapour - some odour suggests some emission.
Developer - not thought hazardous.
Ozone - is produced in significant quantities by older printers. Ventillation advised.
Silicone Oil - used in small quantities in some printers, not considered a hazard.
Summary - Ventilation.
Paper Feed - ideally we want digital book printing, cut sheets through.
Paper Style - Generally aimed at A4 or letter. The 14" form is arely provided.
Paper Tray - Spring plate lifts paper. Guide plates in tray need to be just right.
Paper Quality - usually in range 70 to 120 gsm - more from envelope tray.
Bank Paper - paper down to 60gsm deflects electrostatically.
Letterhead - thick paper with coloured logo and embossing - lasers hate it.
Paper Up Arrow - points to the intended print surface.
Print Jam Epidemics - organisations sometimes get a duff batch of paper.
National Preferences - Paper Sizes. UK users and inkjets like polished paper.
Premature Pickup Problems - buildup of polished material on pickup ollers.
Rejuvenation & Feed Kits - Usually best to replace misfeeding ollers.
Paper Path - registration station ensures lineup and static free surface.
S Paths - paper feeds from underneath then out on top - saves space.
Paper Path Control - combination of clutches, solenoids and paper-dogs.
Unusual Materials - must conform to paper path, electrostatic properties and fuser.
Multiple Trays - plain, letterhead, envelope.
Duplex - double sided print incorporated as standard on some recent printers.
Collators & Staplers - go halfway to producing a book.
Mailboxes - printers can send output to a secure box for collection.
Fuser - Toner is fixed to paper by heat and pressure.
Rollers - standard design is a heated mangle - two rollers at around 150C.
Heater - often a tungsten halide strip lamp inside a metal oller.
Temperature Control - typically a thermistor mounted on a contact pad.
Silicone Oil - used to ensure pages with hot toner separate from the ollers.
Teflon sheet - big surface, rapid startup.
Fuser life - lamp failure, teflon roller or sheet wear, user errors.
Fuser Repair - Can make fusers good as new - if the parts are available.
Colour - a colour laser printer could be 4 successive full mechanisms.
CMYK Process - Cyan, Magenta, Yellow mixed. Black helps.
Intermediate Store - holds the images for 4 successive colours.
Fuser - colour print may need a rather higher fuser capability.
Overall Design - printer gets bigger. Size can be cut by reducing catridges.
Colour Printer Prices -mass production and a big market.
Bigger Market
More Cartridges
Colour Efficiency - Print can slow on colour, low priced USB printers ely on PC.
Operating Costs - conceivably little more than mono - but in practice higher.
Clones & Refills - not recommended if you want accurate colour photographs.
Low Use Costs - Even when colour isn't used a colour printer uses some toner.
Print Times - Can be longer than the manufacturer suggests. More RAM helps.
Is Colour Print Worth It - People are bombarded with messages.
Laser Developments & Notes - laser printing matured over 20 years.
Faster Lasers - A3 page at 2,400dpi a billion pixels.
Faster Polygon Mirrors - more facets or faster spin. Limited purpose in high resolution.
Multiple Lasers - ideally pagewidth, but multiple lasers onto polygon mirror also possible.
Photoconductors - some gory details on OPC.
OPC & Health - .
DLC Coating - Diamond Like Carbon could extend OPC life.
Photo-Electric Research - Associated with LEPs etc.
Silicon - aSi, Germanium, Selenium.
Toner - grain sizes. Not much on chemistry at present?
Colour & Grey-Scale - handling grey-scale with OPC?
Printing Costs - to what extent will laser printing compete with offset litho?
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© Graham Huskinson 2010
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