NUMERICAL CONTROL

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NUMERICAL CONTROL
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Principle of Numerical Control (NC)A system
in which actions are controlled by direct
insertion of numerical data.
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NC Machine ToolFoundation for gt
Robotics gt Flexible Manufacturing Cell gt
Flexible Manufacturing gt CAD/CAM System gt
Computer-Integrated Manufacturing
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Traditional Machine ToolsMilling
MachinesLathesDrilling Boring
MachinesGrinders
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Advantages of NCFlexibilityCapability
for Complex Work-piecesManage Large
Work-piecesReduced Jig Fixture CostHigher
Quality
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NC System ComponentsMachine
ToolMachine-Control Unit gt Data Processing
Unit (DPU) DPU processes coded data from hard
drive passes to CLU. gt Control-Loops Unit
(CLU) Motion control duties. Operates drives
Feedback on actual position. Acts as
a translator for machine commands (motor
on/off, tool speed, distance).
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Direct Numerical ControlAdvantages gt
Library of programs gt Instant modifications gt
Links with CAD gt Increase Information Response
gt Instant Reports
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Computer Numerical Control
(CNC)Advantages gt CRT allows review/editing
gt Pre-check/simulation gt Interface allows more
capability gt Accurate positioning gt More
functions
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CAD/CAMComputer Aided DesignComputer
Aided ManufacturingAdvantages gt Eliminate
blueprints gt Database of parts gt Production
Schedules gt BOM gt Process instructions gt
Simulations
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NC Motion Control ObjectiveExecute precise
motion in a given set of reference frames.gt
Generally described by Cartesian space X-Y-Z.
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NC Position MovementIncrementalgt Taking the
Last position as the zero position.Absolutegt
Locations on Part Fixed Reference Frame with
Home position for reference.
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Degree of Motion ControlPoint-to-Point
(PTP)gt Good for holes slotsgt Position tool
over point.Contouringgt Complex curved
surfacesgt Computers needed for complex
calculationsgt Motion control to motors varying
voltages to DC servo motors.
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NC Part ProgrammingBlock Formatsgt Each block
is a statement.Computer Languagegt Programming
language designed to execute complex
geometrical outlines. gtgtgt APT (Automated
Programming Tool) Geometrical data with motion
statements or NC.
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Available Block FormatsFixed
SequentialBlock AddressTab SequentialWord
Addressgt Used by CNC controller systems.
Alphabetic character is used as a code at the
beginning of each word. Utilize words that
describe an address (identifier) a number that
specifies its content.
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Example of Word AddressN01 G02 X1500
Y2000 F4 S400 T10 N identification numberG
preparatory commandX x axisY y axisZ z
axisI,J,K coordinate valuesF feed
rate Sspindle speedT tool number
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Binary-Coded Decimal (BCD)Machine code
used for numerical control.gt Easier to read than
binary.gt Four binary digits are required to
represent 0 to 9.gt Code that is saved in
RAM.Example 439 10000111001ASCII uses
channels 1 - 4 for digitschannels 5 7
indicate which group (numbers or
alphabetic)channel 8 is for parity.
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