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Overview of Printing
People prefer to read anything substantial in print rather than on a screen. 
Print technology is changing. Inkjets for home users aim at photographic quality. Mass produced colour laser printers can have very low purchase prices.
Transaction printing might be eroded by EDI but businesses don't have common standards and not everyone wants a computer.
Psychologically paper might be important, people seem to retain information better.
Photography and artwork are growing demands which recent printers can meet.
Printer Potential would only be challenged by low cost foldable electronic paper and LEPs.
User Aims create mass markets. Dot matrix & thermal are niches - Inkjets & Laser mainstream. Economies of scale feed back and e-make the market.
Typical aim is to produce something looking like a colour magazine.
Pixels - points of light or ink sufficiently small to be unnoticed on their own which together make up an image. Pixels are normally arranged in a rectangular grid.
Computer screen resolutions - typically about a million pixels at about 75dpi.
Printer resolutions - mostly above 300 dpi -different kind of use, no greyscale.
Greyscale - print processes tend to be binary, they saturate an area with colour or don't print at all.
Halftoning - make an appearance of grey and lighter colours by etching different sized dot patterns and rossettes on printing plates.
Dither - computer mechanisms cant usually change dot size so make patterns of pixels. Swap spatial resolution for greyscale. Human sight merges the result.
Resolution and greyscale limits - providing enough pixels has equired progress.
Memory and greyscale - doubling resolution tends to mean quadrupling memory.
Dither algortithm - neither highly ordered nor random - Floyd-Steinberg.
Colour - RGB 
and CMYK 
process.
True Greyscale - isn't impossible and is highly desireable for photographic material.
Dye sub - highly variable temperature and ink diffusion.
Dot Matrix - overprinting gives a limited sort of greyscale.
Laser Printer - potential for greyscale.
Inkjets - drop size modulation.
Language Support (?)
Colour Gamut - the colour-space available.
Computers & Paper.
Paperless office has been an aim from the first commercial computer on
Information starts in electronic form.
Motors
Encoder Motors - DC motors with a feedback loop
Outline of DC Motor - Stator, Armature, Commutator, Brushes.
Uses - Car starters and wiper motors, video and other recorders, toys. Trams and trains.
Encoder - usually two optical sensors and a slotted disk. Leading opto gives direction.
Support circuit - Motor target, actual and difference. Difference controls a bridge to give off - forward - reverse.
Uses for Encoders - Horizontal drive in inkjets and dotmatrix printers, obots and machine tools.
Cost - Relatively low cost.
Effectiveness - good power to weight ratio and accuracy, quite efficient.
This page is still being worked on © Graham Huskinson 2010