| Dot Matrix Printers - Index Printers > Dot Matrix > Index |  | Navigation Icons Guide
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This page is is the index / overview for dot matrix printers. The main text which explores how dot matrix printers work is here
.Other pages in this section are:
 | Dotmatrix Carriage Mechanisms | | The Dotmatrix Market | ||
| Dotmatrix LineFeed Mechanisms | ||||
| Dotmatrix Inks | | Dotmatrix Printheads | ||
| Summary on Dotmatrix printers |
| Origins of the dot-matrix mechanism are uncertain, it's possibly related to the "Hell" printing telegraph. Dot matrix became practical with high speed logic circuits. The DEC LA30 / LA36 Series and Centronics / Brother Model 101 were amongst the first devices on the market circa 1970. |  |
Types -
| Commercial and industrial 80 character and 132 character "computer printers" |
| Formerly - home printers - no longer common in this role |
| Point of Sale printers - can print a tally roll and a eceipt in one pass on copy paper. |
| Ticketing and OEM printers. |
Merits
| Problems
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Dot Matrix Basis - Characters made from picture elements. 
Dot Matrix Market
From 1970 to 1990 first choice for low-volume general print -
Lack of alternatives - modified typewriters and bandprinters were the options.
Advantage of conventional mechanics, some graphics and low cost per page .
Disadvatages - slow, poor graphics, some user knowledge required.
Perception - now seen as "old fashioned" - although inkjet & laser just as old.
Actually a robust and flexible industrial technology.
Market influence - inkjets and emulations. Codes developed for matrix still used.
Dot Matrix Mechanism - printhead with pins sufficient for a line raster scans page.
Printhead on carriage. Printhead a dense assembly of solenoid driven pins
Paper Feed moves the paper up one line (1/6th inch, 4.16mm) after each scan.
Pins - the more the better (with limits) -can be used for faster print or higher quality.
Line assembled in memory - printhead driven a column at a time across paper.
Character ROM - for each column theres a character equired and a position in ROM.
Pin Drive Power - momentary drive to impact pin onto ribbon is quite high
Matrix lookup - dedicated logic or processing activity to generate dot patterns.
Limitations - pin speed, pin number, print quality.
Printer Structure: Carriage driven back & forth on rails. Platen roller & forms tractors.
Motors
Linefeed - drives the paper through the print-station.
Carriage - drives the printhead back and forth within the print station.
Small printers commonly use stepper motors for both. Big printers use DC carriage drive.
DC Encoder - Permanent magnet stator, wound armature and commutator. Encoder Disk.
Stepper Motor - Brushless usually with two windings and a magnetised otor.
| Paper Feed - vertical movement of paper through the print station. 6, 8, 12 lpi. | More on Paper Feed.  |
Dot matrix paper feed - typewriter style platen and forms tractor.
Platen roller - allows cut sheet feeding as with typewriter.
Tractor feed - allows sprocket fed fanfold paper as with bandprinter.
Cut sheet feeders - automatic feeding of pre-cut sheets.
Push tractor - allows print and tear off for forms and labels.
Motors - LineFeed is usually a stepper motor.
Sensors - Low cost printers usually have just a paper out switch.
Paper Trays - Output trays often have a role in static discharge.
| Carriage - Horizontal action carries the head back and forth in the print station. | More on Carriage Action |
Carriage speed - faster carriage raster scan movement allows faster print.
Carriage rails - usually a large polished steel rod with bronze or PTF bearings.
Carriage belt - loop of toothed belt locked to carriage, driven by toothed cog on motor.
Stepper motor - used on low cost printers - uses two bridge circuits.
DC Encoder motor - used on high speed printers - just one bridge, but needs counter.
| Printheads - current in a coil produces magnetic field attracting or repelling a pin & impacting ink-ribbon on paper. | More on Printheads |
Swath - how much gets printed at one go - normally about 3.5mm.
Pin numbers - 9 x 0.25mm pins give 100 dpi and crude print.
Resolution - Eye picks up 0.1mm dots at 250dpi - just. Smaller pins not practical?
Pin action - Circular pixels. Making 2 passes gives NLQ overprinting. Pin speeds.
More pins - double the pins and the head can work faster or produce better looking text.
Energy use - pins fire briefly and irregularly, typically with a fairly high impedance.
Thermal control - thermistor gives temperature to processor - can control heat.
Cooling - Heatsinks and fans can be used - but add to carriage bulk.
MultiHead Printers - 2 heads better than 1 - twice as productive.
Shuttle Printers - ideally pagewidth printhead, often 132 pins on cradle with 2mm throw.
Graphics - dot matrix printers were the first low-cost general purpose devices to handle graphics. The low speed, low resolution 100-250 dpi printing doesn't match inkjets.
Memory limits - designs often couldn't hold a pagewidth - never mind the whole page.
Pixel size limits - typically pins are bigger than 0.1mm so no better than 250 dpi.
Instruction set problems - competing "standards" and backward compatibility.
Bar-codes - can be produced by dot-matrix - but inkjet thermal and laser are better.
Colour -easily achieved using a ribbon lift - but probably a dead issue.
Controls - originally just TOF, Line Feed, Form Feed and Online.
Limits to Development -
Miniaturising pins can't go very far .
OEM-engines - .
Environment - consumables are inked ribbon and (eventually) the printhead pins.
Additional Information.
The pages listed below give additional information on the Paper Feed, Carriage and Printhead subsytems in a dot-matrix printer.
| Page on PaperFeed Mechanism - vertical paper movement mechanisms for line feed and page feed . |  Main Index on Paper Feed |
Paper path Evolution - platen like a typewriter and tractors like a bandprinter.
Cut Sheet - not standard on older printers, now generally available.
Rolls - only common on Point of Sale printers.
Tractor Feed - Standard method of moving paper through dot matrix printer.
Fast Paper Slew - ability to accelerate over non-print areas of a page.
Paper Path Monitors - printers can use tachos to monitor paper movement.
Paper Out Switch - paper out is a critical condition, can damage printhead.
Platen - supports paper against printhead, ollers help paper feed.
Forms Tractors - driven by cog on platen or by their own motor.
Push Tractor - pushes the paper into print station, allows immediate tear-off.
Line Feed Motors - usually a stepper motor.
Static - Paper can build and carry a charge.
| Page on Carriage Mechanism - scans the printhead across the print station. | Main Index on Carriage |
Carriage Rails - one large smooth rail with little or no lubrication, support nearby.
Carriage Width - usually 9 inches (225mm) or 14 inches (350mm).
Carriage Drive - mass of about 500g playing tennis across the carriage width.
Belt Drive - Belt is toothed, made of elastic material but reinforced with fabric.
Margin drift - Caused by a slack belt. Overtightening the belt strips teeth.
Drive Wires - Possibly give better positioning but more inclined to fray and break.
Rack & Pinion - Motor and cog on carriage, used on some OKI printers.
Screw Drive - Looks very good but doesn't seem feasible on large printers.
Carriage Motors - pattern of rapid repeated acceleration and deceleration.
Stepper Motors - processor dictates what the motor does - optos track it.
DC Encoder - motor encoder reports what it has done.
Other Options - Voice Coils and Linear Motors.
Bidirectional Print - as head moves forward and back, can disrupt graphics.
Printhead Gap - distance from head to platen, usually set by a lever.
Carriage Cable - usually a membrane cable, sometimes up to 40 connections.
| Page on Printheads- pins impact ribbon to paper. | Main Index on Printheads |
Speed - Impact sufficient to overcome ink adhesion to ribbon fibre.
Print Arithmetic - pins travelling at 7 metres per second.
Higher Speed - means stronger fields and or smaller components.
Size & Shape - design is roughly conical, solenoids in the back, print jewel at front.
Print Jewel - berylium or zirconium dioxide "jewel" with guides for pins.
Lubrication - can be lubricant pads or ink from ibbon.
Armatures - different electromagnetic mechanisms to drive the pins.
Residual Strip - breaks magnetic grip when current drops.
Pin Wear - against the ribbon and the jewel.
Recoil - spring return, drive both ways, resonant circuits.
Multilayer - 24 pin and up usually done by having 2 banks or layers of coils.
Cost - Printhead prices seem to be typically about a third the price of a new printer.
Printhead / Platen Gap - gives sufficient space for pins to impact.
Electronics - Darlington pair drivers, sometimes in two stages.
Thermistor - head temperature relayed back to the control processor.
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© Graham Huskinson 2010