Operational Features of CNC
Operational Features of CNC
Machine
A CNC control system Machine
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
CNC Machine Feedback
CNC Machine Feedback
Devices
Devices
Lecture 24
Lecture 24
Engineering 475
Engineering 475
Automated Production Systems
Automated Production Systems
Degarmo, Figure 29-10.
What are Potentiometers?
What are Potentiometers?
Position Feedback Options
Position Feedback Options
Material with
constant
Potentiometers
Resolvers Encoders
Resolvers
resistance per
unit length
properties
Wiper Vo
L
V
´ = L
Linear
Rotary
Linear
Rotary
Vo
´
V
Position can be
computed from
voltage ratios.
Potentiometers
Potentiometers
What are Encoders?
What are Encoders?
(Examples)
(Examples)
A device used to convert linear or rotational
position information into an electrical output
signal.
Magnetic
Magnetic
Capacitive
Capacitive
(LVDT)
(LVDT)
Encoder
Encoder
Physics
Physics
Contacting
Optical
Contacting
Optical
www.betatronix.com
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How Does a Rotary Optical
How Does a Rotary Optical
Incremental Encoders
Incremental Encoders
Encoder Work?
Encoder Work?
" Outer track is used to Incremental Encoder - Produces equally spaced
determine position. pulses from one or more concentric tracks on the
code disk. Position is determined by counting
" Middle track is used
pulses
to measure direction
of rotation.
Incremental Encoder
" Inner track is used to
must be calibrated.
indicate a complete
Power loss will lead to
revolution.
loss of position
" Integrated counter
information unless
circuits are used to
backup power source is
count leading or falling
used.
edges of pulses.
Compliments of BMC Buckbee-Mears St. Paul
Bateson, Fig. 7.12
Absolute Encoders
Absolute Encoders
Gray Binary Code
Gray Binary Code
Absolute Encoder  produces a binary number
that uniquely identifies each position on the code
disk.
" Absolute encoders
do not have to be
recalibrated after
a power loss.
" Absolute encoders
are more expensive
than incremental
encoders.
Bateson, Fig. 7-15
Compliments of BMC Buckbee-Mears St. Paul
How Does a Linear Optical
How Does a Linear Optical
MTD Bridgeport
MTD Bridgeport
Encoder Work?
Encoder Work?
Typical Acu-lite
Encoder Accuracy
" Linear instead of
Ä… 5 µm m
rotary scale.
" Glass is used because
or
of low sensitivity to
Ä… 0.0002 in/yd
temperature changes.
Acu-lite Glass Scale Encoder
Precision Glass Scale Encoder
www.theproductfinder.com
www.anilam.com
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Industrial Applications What are Resolvers?
Industrial Applications What are Resolvers?
Rotary Encoders are widely
used with robotics.
Linear encoders are widely
used with machine tools.
A resolver is a rotary transformer that produces an
output signal that is a function of the rotor position.
Bateson, Fig. 7.10
Operational Features of CNC
Operational Features of CNC
Servomotor with Resolver
Servomotor with Resolver
Machine
Machine
A CNC control system
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
Parker, Fig. 1-44
Degarmo, Figure 29-10.
Rotary Encoder Velocity
Velocity Feedback Rotary Encoder Velocity
Velocity Feedback
(Example)
(Example)
Tc
C
Electrical output is proportional
Tachometers
60C
to rate of angular rotation.
S =
NTc
N
Encoders, Number of pulses per time is
Resolvers, proportional to rate change of
Potentiometers position. S = shaft speed, rpm
N = number of pulses per shaft revolution
C = total count during time interval Tc
What is velocity
Tc = counter time interval, seconds
resolution?
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Operational Features of CNC
Operational Features of CNC
CNC Programming Methods
CNC Programming Methods
A CNC control system
Machine
Machine
includes a velocity loop
within an axis drive system
and a position loop external
to the axis drive system.
Computer Aided
Manual
Manufacturing
(CAM)
Main Control Unit
Main Control Unit
Degarmo, Figure 29-10.
Main Controller User Interfaces
Main Controller User Interfaces Types of CNC Programming
Types of CNC Programming
Languages
Languages
Proprietary
Standard
(Conversational)
ISO 6983 Respond to prompts
EIA RS274 Typically proprietary
Command List
Who and what is EIA?
Who and what is EIA?
Who and What is ISO?
Who and What is ISO?
Electronic Industries Association
World wide
U.S. Manufacturers of
standards
electronic equipment.
organization
ISO  means
one
www.iso.ch
www.eia.org/eng/published.htm
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Example of ISO 6983 and EIA
Example of ISO 6983 and EIA
ISO 6983 and EIA RS274
ISO 6983 and EIA RS274
RS274 Standard Code
RS274 Standard Code
" Standards are very similar
" EIA 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
Often referred to as M-code or G-code
Nanfara, pg 35
Steps in the CNC Process
Steps in the CNC Process
Major Manufacturers of ISO and EIA
Major Manufacturers of ISO and EIA
(Manual Programming)
(Manual Programming)
Main Controllers
Main Controllers
1. Review part drawing
2. Decide which machine will produce the part
3. Choose the tooling required
4. Decide on the machining sequence
General Electric
General Electric
Fanuc
Fanuc
5. Do math calculations to find part coordinates
6. Calculate the spindle speeds and feedrates required
for the tooling and part material
Cincinnati Milicron
Cincinnati Milicron
7. Write the CNC program
8. Prepare setup sheets and tool lists
9. Verify the program using a CNC simulator or the
actual machine
Bendix
Bendix
Giddings and Lewis
Giddings and Lewis
10. Edit the program if necessary
11. Run the program and produce the part
Nanfara, pg 11.
Steps in the CNC Process
Steps in the CNC Process
What is a 3-D CAD model?
What is a 3-D CAD model?
(CAM)
(CAM)
1. Develop the three-dimensional geometric model of the
" A 3-D cad model is a computer
part using CAD
representation of an actual part.
2. Decide which machining operations are required to
produce the part
" The computer representation
3. Choose the tooling to be used
contains all of the physical
4. Run a CAM software program to generate the CNC part
information about the part
program, including the setup sheets and list of tools
(material, dimensions, etc.)
5. Verify the program on a machine simulator
6. Download the part program(s) to the appropriate
" The mathematical descriptions of
machine(s)
the model s surfaces can be used
7. Verify the program(s) on the actual machine(s) and edit if
to create CNC code.
necessary
8. Run the program(s) and produce the part
Nanfara, pg. 11.
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Integrated Design and Manufacturing
Integrated Design and Manufacturing
Assignment
Assignment
A good designer must know
Review information about ISO and EIA on the web.
how a part will be produced and
what 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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