class 2 - slides int cnc programm
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Introduction to CNCIntroduction to CNC
ProgrammingProgramming
Class 2Class 2
Bob LeMaster, Ph.D.Bob LeMaster, Ph.D.
College of EngineeringCollege of Engineering
University of Tennessee at MartinUniversity of Tennessee at Martin
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Operational Features of CNCOperational Features of CNC
MachineMachine
Degarmo, Figure 29-10.
A CNC control system
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
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Primary Machine ControlPrimary Machine Control
ElementsElements
Parker, Fig. 5.1
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Position Feedback OptionsPosition Feedback Options
Potentiometers Encoders
Linear RotaryLinear Rotary
ResolversResolvers
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What are Potentiometers?What are Potentiometers?
Material with
constantresistance per
unit length
propertiesWiper
V
Vo
LV
V!
o
=L
!
Position can becomputed from
voltage ratios.
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PotentiometersPotentiometers(Examples)(Examples)
www.betatronix.com
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What are Encoders?What are Encoders?A device used to convert linear position
information into an electrical output signal.
Encoder
Physics
Encoder
Physics
Magnetic
(LVDT)
Magnetic
(LVDT)
OpticalOptical ContactingContacting
CapacitiveCapacitive
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How Does a Rotary OpticalHow Does a Rotary Optical
Encoder Work?Encoder Work?
Bateson, Fig. 7.12
Outer track is used to
determine position.
Middle track is used
to measure direction
of rotation.
Inner track is usedto indicate a
complete revolution.
Integrated counter
circuits are used to
count leading or
falling edges of
pulses.
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Incremental EncodersIncremental EncodersIncremental Encoder - Produces equally spaced
pulses from one or more concentric tracks on the
code disk. Position is determined by counting
pulses
Compliments of BMC Buckbee-Mears St. Paul
Incremental Encodermust be calibrated.
Power loss will lead to
loss of position
information unlessbackup power source is
used.
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Absolute EncodersAbsolute Encoders
Compliments of BMC Buckbee-Mears St. Paul
Absolute Encoder produces a binary number
that uniquely identifies each position on the code
disk.
Absolute encoders
do not have to be
recalibrated after apower loss.
Absolute encoders
are more expensivethan incremental
encoders.
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Gray Binary CodeGray Binary Code
Bateson, Fig. 7-15
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How Does a Linear OpticalHow Does a Linear Optical
Encoder Work?Encoder Work?
www.anilam.comPrecision Glass Scale Encoder
Linear instead of
rotary scale.
Glass is used
because of low
sensitivity totemperature changes.
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MTD BridgeportMTD Bridgeport
Acu-lite Glass Scale Encoder
www.theproductfinder.com
in/yd0002.0
or
mm5
Typical Acu-lite
Encoder Accuracy
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Industrial ApplicationsIndustrial Applications
Rotary Encoders are widely used with robotics.
Linear encoders are widely used with machine tools.
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What areWhat are ResolversResolvers??
A resolver is a rotary transformer that produces an
output signal that is a function of the rotor position.
Bateson, Fig. 7.10
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Servomotor withServomotor with ResolverResolver
Parker, Fig. 1-44
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Operational Features of CNCOperational Features of CNC
MachineMachine
Degarmo, Figure 29-10.
A CNC control system
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
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Velocity FeedbackVelocity Feedback
TachometersElectrical output is
proportional to rate ofangular rotation.
Encoders,
Resolvers,
Potentiometers
Number of pulses per time is
proportional to rate change of
position.
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Rotary Encoder VelocityRotary Encoder Velocity(Example)(Example)
cNT
60CS =
secondsinterval,mecounter tiT
TintervaltimeduringcounttotalC
revolutionshaftperpulsesofnumberN
rpmspeed,shaftS
c
c
=
=
=
=
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Operational Features of CNCOperational Features of CNC
MachineMachine
Degarmo, Figure 29-10.
A CNC control system
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
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CNC Programming MethodsCNC Programming Methods
ManualComputer AidedManufacturing
(CAM)
Main Control UnitMain Control Unit
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Main Controller UserMain Controller User
InterfacesInterfaces
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Types of CNC ProgrammingTypes of CNC ProgrammingLanguagesLanguages
Standard Proprietary(Conversational)
ISO 6983
EIA RS274
Respond to prompts
Typically proprietary
MTD Big Machine MTD Small Machine
Command List
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Who and what is EIA?Who and what is EIA?
www.eia.org/eng/published.htm
Electronic Industries Association
U.S. Manufacturers ofelectronic equipment.
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Who and what is ISO?Who and what is ISO?
www.iso.ch
World wide
standardsorganization
ISO means
one
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ISO 6983 and EIA RS274ISO 6983 and EIA RS274
Standards are very similarEIA in most cases will adopt an ISO
standard with only minor changes
and issue the standard under an EIA
number.CAD/CAM programs support these
standards
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Example of ISO 6983 andExample of ISO 6983 and
EIA RS274 Standard CodeEIA RS274 Standard Code
Nanfara, pg 35
Often referred to as M-code or G-code
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Major Manufacturers of ISOMajor Manufacturers of ISOand EIA Main Controllersand EIA Main Controllers
Fanuc General Electric
Bendix
Cincinnati Milicron
Giddings and Lewis
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Steps in the CNC ProcessSteps in the CNC Process(Manual Programming)(Manual Programming)
1. Review part drawing
2. Decide which machine will produce the
part3. Choose the tooling required
4. Decide on the machining sequence
5. Do math calculations to find part
coordinates6. Calculate the spindle speeds and feedrates
required for the tooling and part material
7. Write the CNC program
8. Prepare setup sheets and tool lists9. Verify the program using a CNC simulator
or the actual machine
10. Edit the program if necessary
11. Run the program and produce the part Nanfara, pg 11.
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Steps in the CNC ProcessSteps in the CNC Process(CAM)(CAM)
1. Develop the three-dimensional geometric
model of the part using CAD
2. Decide which machining operations arerequired to produce the part
3. Choose the tooling to be used
4. Run a CAM software program to generate
the CNC part program, including the setupsheets and list of tools
5. Verify the program on a machine simulator
6. Download thee part program(s) to the
appropriate machine(s)
7. Verify the program(s) on the actual
machine(s) and edit if necessary
8. Run the program(s) and produce the part Nanfara, pg. 11.
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What is a 3What is a 3--D CAD model?D CAD model?
A 3-D cad model is a computer
representation of an actual part.
The computer representation
contains all of the physical
information about the part(material, dimensions, etc.)
The mathematical descriptions
of the models surfaces can beused to create CNC code.
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Integrated Design andIntegrated Design and
ManufacturingManufacturingA good designer must know
how a part will be produced andwhat tooling will be used to
make it.
This part is made using sand casting
technology.
The patterns are machined using a
three-axis CNC mill.Finish machining is done using a
three-axis CNC mill.
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AssignmentAssignment
Review the material from the first two
classes.
There will be an exam at the beginning ofthe next class.
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What will we do next class?What will we do next class?
We will start learning how to program amill using the ISO and EIA standard
commands.
Bring a calculator if you have one.