• Electromechanical device
  • Computer interface – links computer & printer – commands & data, Printer Status
  • Printer Electronics – decode command, generate control signals, activate print mechanism

Mechanical assemblies – print assembly, paper movement assembly & sensor assembly

Printer Functions

  • Receives printable data char & non-printable control char

Control characters:

Symbol

 

Control Characters

Function

CR

Carriage Return

Return to 1st column

LF

Line Feed

Skip one line

FF

Form Feed

Skip paper to beginning of next page

Each page – form.

Character

Indicates

Specified as

SPEED

How fast a printer works

CPS – Characters per second,

 LPM – Lines per min, 

PPM – Pages per min

QUALITY

How good the shape of printed character is 

DRAFT, NQL – Near Letter Quality

LQP – Letter Quality Printer

CHARACTER SET

Total no. of data characters & control characters

  

INTERFACE

  

Parallel form / Serial form

BUFFER SIZE

Data char in buffer memory

  

PRINT MECHANISM

  

Dot matrix, daisy wheel, golfball, thermal, band, belt, drum train, chain, inkjet, laser.

PRINT MODE

  

Serial/ Parallel

PRINT SIZE

  

Character size, No. of char per line

PRINT DIRECTION

  

Unidirectional, Bidirectional, reverse, logic seeking

Common forms of paper

  • Single sheets
  • Fan fold
  • Roll

Paper Movement

  • Friction feed
  • Tractor feed
  • Pin feed
  • Sheet feed

Modules inside a printer

  • Print-head Mechanism
  • Carriage Movement
  • Paper feed
  • Control electronics
  • Interface logic
  • Power Supply

Printer Types

1.Based on printing technique

1. Impact printer

  • Character formed by physical contact of print head on ink ribbon/ paper
  • Eg: Dot matrix printer, Daisy Wheel, Golf ball, Drum, band, Chain

2. Non- impact printer

  • No physical contact of head with paper or ribbon
  • Eg:  Laser printer, thermal, inkjet & electrostatic printer.

2. Based on Printing sequence

1. Character printer (Serial Printer)

  • Characters printed one after the other
  • i.e., one character at a time
  • E.g: Daisy wheel printer, Dot matrix printer.

2. Line Printer (Parallel Printer) 

  • Prints a complete line (many characters) in one shot
  • Eg: Drum printer, band, chain printer
  • High speed & specified in CPS, LPM or PPM

3. Based on Print Quality

1. Draft Printer

  • Print character is formed by closely spaced dots
  • Visible but not impressive
  • Eg: Dotmatrix printer

2. LQP (Letter Quality Printer)

  • Whole char is formed as letter (|||r to type writer)
  • Pleasant to read, used in office
  • Eg: Daisy wheel printer

3. NQL (Near Letter Quality Printer)

  • Prints char as pattern of dots & prints twice – Offset 
  • More Impressive

4. Based on Print Interface

1. Parallel Interface Printer

Eg:  Centronics with 36 pins

2. Serial Interface Printer

Eg:  RS 232 C

5. Based on Print Direction

1. Unidirectional Printer

  • Print head moves in only one direction (left to right)
  • |||r to manual typewriter

2. Bidirectional Printer

  • Printing is performed during both direction of head movement (left to right & right to left)

3. Reverse Printer

 

6. Based on Printing sequence

1. Daisy Wheel Printer

  • Print head has circular wheel with 96 spokes/character 

  • Each spoke has a raised char embossed at tip

Working

  • Rotate wheel till desired char is on paper
  • Solenoid driven hammer strikes petal & ribbon & paper
  • Move print head to next column

Pros: Good quality print

Easy Font interchange

Speed:  10 – 60  CPS Eg: QUALTERM 45/55 & DATA TERMINALS 302

2. Dot Matrix Impact Printer

  • Character – dots using 7 by 5 matrix pattern of dots

  • Print head – pins & solenoid 

  • Head moves column by column to print a character
  • Quality is _______________
  • By using greater number of pins or printing twice with a sight offset for dots _______ is achieved

Advantages

  • Print graphics – sequential dots
  • Print in any language, no hardware change
  • Colour printing by colour ribbons
  • Lower price

Speed

  • Draft mode – 100 to 300 cps
  • NQL mode – 25 to 50 cps

Eg

  • WIPRO FX 105, CENTRONICS 702, DATA PRODUCTS M 200, DIABLO SYSTEMS 2300, HP 2635 A

Golf – Ball Printer

  • Characters embossed in spherical golf-ball metallic unit

  • Drive mechanism moves the ball to print desired character

  • Ball is pushed over ribbon to print leter on paper

Adv:

  • Excellent Print quality
  • Font can easily be changed by changing the ball

Speed:

  • less – 10 to 15 CPS

Thermal Printer

  • Special heat sensitive paper
  • Print head – heating elements
  • Char printed as matrix of dots
  • On switching ON heating element, spot on paper heated & turns dark – creates letter.
  • Also, normal paper but heat sensitive ribbon
  • Consistent print quality
  • High Running cost due to special paper/ribbon

Laser Printer

  • |||r  to xerox machine
  • Laser creates image on photosensitive drum
  • Laser turned ON & OFF – sweeps back & forth across the drum
  • Image inked by applying toner on drum. Electrostatically transferred from drum to paper
  • Popular – Hewlett-Packard Laser jet
  • High Letter quality & Speed
  • High Price

LED Printer

  • Instead of Laser Light emitting Diodes (LEDs) used to expose from drum
  • No moving parts

Ink Jet Printer

  • Better Quality printout
  • Very sharp output
  • Cheaper
  • Colour print
  • No pins or ribbon / matrix of dots

  • Tiny dots of ink is sprayed onto paper
  • When print head moves across paper, jets spray ink to form letters
  • has 48 to 128 pins
  • Print quality – Dots per inch  (dpi)
  • Deskjet & Bubblejet are standard Ink jets
  • Eg: Hawlett- Packard, Canon, Epson & Lexmark