Advanced Manufacturing Industrial Robotics

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Advanced Manufacturing Industrial Robotics
Dr. L. K. Gaafar
This presentation uses information from
http//www.glue.umd.edu/aksamuel/academic/Viewgra
ph_files/frame.htm
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Industrial Robots Definition
A robot is a programmable arm simulator
A robot is a programmable, multifunction
manipulator designed to move material, parts,
tools, or special devices through variable
programmed motions for the performance of a
variety of tasks Robot Institute of America
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The Advent of Industrial Robots
Motivation for using robots to perform task which
would otherwise be performed by humans.
Safety Efficiency Reliability Worker
Redeployment Cost reduction
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Industrial Robots Types
Pick and Place
Simplest kind of industrial robot Perform
simple pickup and drop functions Cannot sense
environment The limits of motion of each joint
of the machine are fixed by electric or pneumatic
impulse originating at a plug-board control
panel Still some on production lines but are
being phased out
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Industrial Robots Types
Servo Robots
A more sophisticated level of control can be
achieved by adding servomechanisms that can
command the position of each joint. The
measured positions are compared with commanded
positions, and any differences are corrected by
signals sent to the appropriate joint actuators.
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Main Components of Industrial Robots
Arm or Manipulator End effectors Drive
Mechanism Controller Custom features e.g.
sensors and transducers
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Arm or Manipulator
The main anthropomorphic element of a robot.
In most cases the degrees of freedom depends on
the arm The work volume or reach mostly
depends on the functionality of the Arm
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End Effectors
Device attached to the robots wrist to perform a
specific task
Grippers Mechanical Grippers Suction cups or
vacuum cups Magnetized grippers Hooks
Scoops (to carry fluids)
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End Effectors
Device attached to the robots wrist to perform a
specific task
Tools Spot Welding gun Arc Welding tools
Spray painting gun Drilling Spindle Grinders,
Wire brushes Heating torches
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Sensors in robotics
Types of sensors Tactile sensors (touch
sensors, force sensors, tactile array sensors)
Proximity and range sensors (optical sensors,
acoustical sensors, electromagnetic sensors)
Miscellaneous sensors (transducers and sensors
which sense variables such temperature, pressure,
fluid flow, thermocouples, voice sensors)
Machine vision systems
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Sensors in robotics
Uses of sensors Safety monitoring Interlocks
in work cell control Part inspection for
quality control Determining positions and
related information about objects
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Sensors in robotics
Desirable features of sensors Accuracy Operation
range Speed of response Calibration Reliability Co
st and ease of operation
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Physical Configuration
Cylindrical
Cartesian
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Physical Configuration
Polar (Spherical)
Jointed Arm
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Programming Robots
Manual Cams, stops etc Walkthrough
(Lead-through) Manually move the arm, record to
memory Manual teaching Teach pendant
Off-line programming Similar to NC part
programming VAL, RAPT
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Applications
Material Handling/Palletizing Machine
Loading/Unloading Arc/Spot Welding Water
jet/Laser cutting Spray Coating
Gluing/Sealing Investment casting Processing
operations Assembly Inspection
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Performance Specifications of Industrial Robots
Motion control path control velocity
control Types of drive motors hydraulic
electric pneumatic
Size of the working envelope Precision of
movement Control resolution Accuracy
Repeatability Lifting capability Number of
robot axes Speed of movement maximum speed
acceleration/deceleration time
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Work Volume
Spatial region within which the end of the
robots wrist can be manipulated
Determined by Physical configurations
Size Number of axes The robot mounted
position (overhead gantry, wall- mounted, floor
mounted, on tracks) Limits of arm and joint
configurations The addition of an end-effector
can move or offset the entire work volume
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Robot Control
Simple
Control is simpler for a robot arm which can
always expect objects to be oriented in the same
way. Only the robots coordinate system has to
be controlled. The math gets complex but is
manageable
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Robot Control
More Complex
It gets more complex when you expect an arm to
pick up objects which can be in any
orientation. There are several problems - How
do you pick it up? - How do you recognize it is
there? - How do you know you are holding it
firmly? - How do you have to change your grip to
hold it the way you need to? This is still a
subject of much research
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Precision of Movement
Precision with which, the robot can move the end
of its wrist
Depends mainly on the controller
Spatial/Control resolution Accuracy
Repeatability
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Spatial Resolution
Smallest increment of motion at the wrist end
that can be controlled by the robot
Depends on the position control system, feedback
measurement, and mechanical accuracy
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Accuracy
Capability to position the wrist at a target
point in the work volume
One half of the distance between two adjacent
resolution points Affected by mechanical
Inaccuracies Manufacturers dont provide the
accuracy (hard to control)
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Repeatability
Ability to position back to a point that was
previously taught
Repeatability errors form a random variable.
Mechanical inaccuracies in arm, wrist
components Larger robots have less precise
repeatability values
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Weight Carrying Capacity
The lifting capability provided by manufacturer
doesnt include the weight of the end effector
Usual Range 2.5lb-2000lb Condition to be
satisfied Load Capability gt Total Wt. of
workpiece Wt. of end effector Safety range
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Speed of Movement
Speed with which the robot can manipulate the end
effector
Acceleration/deceleration times are crucial for
cycle time. Determined by Weight of the
object Distance moved Precision with
which object must be positioned
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Motion Control
Path control - how accurately a robot traces a
given path (critical for gluing, painting,
welding applications) Velocity control - how
well the velocity is controlled (critical for
gluing, painting applications) Types of
control path - point to point control (used in
assembly, palletizing, machine loading) -
continuous path control/walkthrough (paint
spraying, welding).- controlled path (paint
spraying, welding).
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Type of Drive System
Hydraulic High strength and high speed
Large robots, Takes floor space Mechanical
Simplicity Used usually for heavy payloads
Electric Motor (Servo/Stepper) High accuracy
and repeatability Low cost Less floor
space Easy maintenance Pneumatic
Smaller units, quick assembly High cycle
rate Easy maintenance
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Robot Applications (Configurations/Characteristics
)
SCARA Robot (Selective Compliance Assembly Robot
Arm)
Characteristics Repeatability lt 0.025mm
(high) No. of axes min 4 axes Vertical
motions smoother, quicker, precise (due to
dedicated vertical axis) Good vertical
rigidity, high compliance in the horizontal
plane. Working envelope range lt 1000mm
Payload10-100 kg Speed fast 1000-5000mm/s
Applications Precision, high-speed, light
assembly
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Robot Applications (Configurations/Characteristics
)
Cylindrical Coordinate Robot
Characteristics Wide range of sizes
Repeatability vary 0.1-0.5mm No. of axes
min 3 arm axes (2 linear)Working envelope
typically large (vertical stroke as long as
radial stroke) The structure is not compact.
Payload 5 - 250kg Speed 1000mm/s, average
Cost inexpensive for their size and payload
Applications Small robots precision small
assembly tasks Large robots material handling,
machine loading/unloading.
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Robot Applications (Configurations/Characteristics
)
Vertical Articulated Arm Robot
Characteristics Repeatability 0.1-0.5mm
(large sizes not adequate for precision assembly)
No. of axes 3 rotary arm-axes, 2-3 additional
wrist axis (excellent wrist articulation)
Working envelope large relative to the size,
Structure compact, but not so rigid Payload
5-130kg Tool tip speed fast 2000mm/s
Applications Welding, painting, sealing,
deburring, and material handling
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Robot Applications (Configurations/Characteristics
)
Spherical Coordinate Robot
Characteristics Repeatability poor 0.5-1mm
No. of axes 3 arm-axes (1 linear radial), 1-2
additional wrist-axes. Working envelope large
vertical envelope relative to the unit size
Payload 5-100 kg Speed low (linear motions
are not smooth and accurate- require coordination
of multiple axes)
Applications Material handling, spot welding,
machine loading
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Robot Applications (Configurations/Characteristics
)
Cartesian Coordinate Robot
Characteristics Repeatability high
(0.015-0.1) No. of axes 3 linear arm-axis,
Working enveloperelative large Payload5-
100kg Speed fast
Applications Precise assembly, arc welding,
gluing, material handling
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Robot Applications (Configurations/Characteristics
)
Gantry Robot
Characteristics Repeatability 0.1-1mm No.
of axes 3 linear traverse-axes, 1-3 additional
wrist axes Working envelope very large
Payload vary function of size, support very
heavy 10-1000kg Speed low for large masses
Applications Handling very large parts, moving
material on long distances, welding, gluing.
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What to Automate
Simple Repetitive operations. Cycle times
greater than 5s. Parts can be delivered in
proper locations/orientation. Part weight is
suitable. One or two persons can be replaced in
24 hr period. Setups and changeovers are not
frequent.
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Robot Implementation Planning
Identify Objectives (Benefits) Increase
productivity Reduce labor cost Reduce cycle
time Eliminate undesired jobs Safety
reasons protect from exposure to hazardous
conditions Increase product quality
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Robot Implementation Planning
Consider Drawbacks The impact upon the
workers The impact upon production schedule
and maintenance Questions of potential model
changes or process changes
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Robot Implementation Planning
Fixed versus Flexible Automation
Fixed automation ExpensiveCan become obsolete
early (dedicated for a single task)Large
inventoriesDifficulties in commissioning and
high maintenance costsFaster and more accurate
Flexible (robot) automationReprogrammable for
different tasksQuick to commissionEasy to
maintainCheaper to design.
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Economical Justification
Two robots are to be considered for a particular
application. The following data are available
Assume MARR 10
The life of each robot is assumed to be 5 years,
with yearly variable costs (indirect, operating,
maintenance) as follows

• Assuming unlimited demand and 250 working 24-hour
  days, which robot is more economical?
• Determine the Economic service life of the best
  choice assuming that it loses 20 of its value
  every year.

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