MIDDLE EAST TECHNICAL UNIVERSITY
Mechanical Engineering Department
ME 445
Integrated Manufacturing
Systems
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ROBOTICS
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Robotics Terminology
Robot: An electromechanical device with multiple degreesof-freedom (DOF) that is programmable to accomplish a
variety of tasks.
Industrial robot:The Robotics Industries Association
(RIA) defines robot in the following way:
“An industrial robot is a programmable, multifunctional manipulator designed to move materials,
parts, tools, or special devices through variable
programmed motions for the performance of a
variety of tasks”
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Robotics Terminology
Robotics: The science of robots. Humans working in this
area are called roboticists.
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Robotics Terminology
DOF degrees-of-freedom: the number of independent
motions a device can make. (Also called mobility)
five degrees of freedom
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Robotics Terminology
Manipulator: Electromechanical device capable of
interacting with its environment.
Anthropomorphic: Like human beings.
ROBONAUT (ROBOtic astroNAUT), an anthropomorphic robot with two arms,
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two hands, a head, a torso, and a stabilizing leg.
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Robotics Terminology
End-effector: The tool, gripper, or other device mounted at
the end of a manipulator, for accomplishing useful tasks.
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Robotics Terminology
Workspace: The volume in space that a robot’s endeffector can reach, both in position and orientation.
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A cylindrical robots’ half workspace
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Robotics Terminology
Position: The
something.
translational
(straight-line)
location
of
Orientation: The rotational (angle) location of something. A
robot’s orientation is measured by roll, pitch, and yaw angles.
Link: A rigid piece of material connecting joints in a robot.
Joint: The device which allows relative motion between two
links in a robot.
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A robot joint
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Robotics Terminology
Kinematics: The study of motion without regard to forces.
Dynamics: The study of motion with regard to forces.
Actuator: Provides force for robot motion.
Sensor: Reads variables in robot motion for use in control.
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Robotics Terminology
Speed
•The amount of distance per unit time at which the robot
can move, usually specified in inches per second or
meters per second.
•The speed is usually specified at a specific load or
assuming that the robot is carrying a fixed weight.
•Actual speed may vary depending upon the weight carried
by the robot.
Load Bearing Capacity
•The maximum weight-carrying capacity of the robot.
•Robots that carry large weights, but must still be precise
are expensive.
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Robotics Terminology
Accuracy
•The ability of a robot to go to the specified position
without making a mistake.
•It is impossible to position a machine exactly.
•Accuracy is therefore defined as the ability of the robot to
position itself to the desired location with the minimal
error (usually 25 mm).
Repeatability
•The ability of a robot to repeatedly position itself when
asked to perform a task multiple times.
•Accuracy is an absolute concept, repeatability is relative.
•A robot that is repeatable may not be very accurate, visa
versa.
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Robotics Terminology
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Robotics History
350 B.C
The Greek mathematician, Archytas builds a mechanical
bird named "the Pigeon" that is propelled by steam.
322 B.C.
The Greek philosopher Aristotle writes;
“If every tool, when ordered, or even of its own accord,
could do the work that befits it... then there would be no
need either of apprentices for the master workers or of
slaves for the lords.”...
hinting how nice it would be to have a few robots around.
200 B.C.
The Greek inventor and physicist Ctesibus of Alexandria
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designs water clocks that have movable figures on them. 14
Robotics History
1495
Leonardo Da Vinci designs a mechanical device that looks
like an armored knight. The mechanisms inside "Leonardo's
robot" are designed to make the knight move as if there was
a real person inside.
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Robotics History
Leonardo’s Robot
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Robotics History
1738
Jacques de Vaucanson begins building automata. The
first one was the flute player that could play twelve songs.
1770
Swiss clock maker and inventor of the modern wristwatch
Pierre Jaquet-Droz start making automata for European
royalty. He create three doll, one can write, another plays
music, and the third draws pictures.
1801
Joseph Jacquard builds an automated loom that is
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controlled with punched cards.
Robotics History
Joseph Jacquard’s Automated
Loom
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Robotics History
1898
Nikola Tesla builds and demonstrates a remote controlled
robot boat.
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Robotics History
1921
Czech writer Karel Capek introduced the word "Robot" in his
play "R.U.R" (Rossuum's Universal Robots). "Robot" in Czech
comes from the word "robota", meaning "compulsory labor“.
1940
Issac Asimov produces a series of short stories about robots
starting with "A Strange Playfellow" (later renamed "Robbie")
for Super Science Stories magazine. The story is about a
robot and its affection for a child that it is bound to protect.
Over the next 10 years he produces more stories about robots
that are eventually recompiled into the volume "I, Robot" in
1950. Issac Asimov's most important contribution to the
history of the robot is the creation of his “Three Laws of
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Robotics”.
Robotics History
Three Laws of Robotics:
1. A robot may not injure a human being, or, through
inaction, allow a human being to come to harm.
2. A robot must obey the orders given it by human beings
except where such orders would conflict with the First
Law.
3. A robot must protect its own existence as long as such
protection does not conflict with the First or Second
Law.
Asimov later adds a "zeroth law" to the list:
Zeroth law: A robot may not injure humanity, or, through
inaction, allow humanity to come to harm.
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Robotics History
1946
George Devol patents a playback device for controlling
machines.
1961
Heinrich Ernst develops the MH-1, a computer operated
mechanical hand at MIT.
1961
Unimate, the company of Joseph Engleberger and George
Devoe, built the first industrial robot, the PUMA
(Programmable Universal Manipulator Arm).
1966
The Stanford Research Institute creates Shakey the first
mobile robot to know and react to its own actions.
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Robotics History
Unimate PUMA
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SRI Shakey
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Robotics History
1969
Victor Scheinman creates the Stanford Arm. The arm's
design becomes a standard and is still influencing the design
of robot arms today.
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Robotics History
1976
Shigeo Hirose designs the Soft Gripper at the Tokyo
Institute of Technology. It is designed to wrap around an
object in snake like fashion.
1981
Takeo Kanade builds the direct drive arm. It is the first to
have motors installed directly into the joints of the arm. This
change makes it faster and much more accurate than
previous robotic arms.
1989
A walking robot named Genghis is unveiled by the Mobile
Robots Group at MIT.
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Robotics History
1993
Dante an 8-legged walking robot developed at Carnegie
Mellon University descends into Mt. Erebrus, Antarctica. Its
mission is to collect data from a harsh environment similar
to what we might find on another planet.
1994
Dante II, a more robust version of Dante I, descends into
the crater of Alaskan volcano Mt. Spurr. The mission is
considered a success.
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Robotics History
1996
Honda debuts the P3.
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Robotics History
1997
The Pathfinder Mission lands on Mars
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1999
SONY releases the AIBO robotic pet.
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Robotics History
2000
Honda debuts new humanoid robot ASIMO.
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Industrial Robots
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Power Sources for Robots
• An important element of a robot is the
drive system. The drive system supplies
the power, which enable the robot to
move.
• The dynamic performance of a robot
mainly depends on the type of power
source.
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There are basically three types of
power sources for robots:
1. Hydraulic drive
• Provide fast movements
• Preferred for moving heavy parts
• Preferred to be used in explosive
environments
• Occupy large space area
• There is a danger of oil leak to the shop
floor
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2. Electric drive
• Slower movement compare to the
hydraulic robots
• Good for small and medium size robots
• Better positioning accuracy and
repeatability
• stepper motor drive: open loop control
• DC motor drive: closed loop control
• Cleaner environment
• The most used type of drive in industry
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3. Pneumatic drive
• Preferred for smaller robots
• Less expensive than electric or hydraulic
robots
• Suitable for relatively less degrees of
freedom design
• Suitable for simple pick and place
application
• Relatively cheaper
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Robotic Sensors
• Sensors provide feedback to the control
systems and give the robots more
flexibility.
• Sensors such as visual sensors are useful
in the building of more accurate and
intelligent robots.
• The sensors can be classified as follows:
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1. Position sensors:
Position sensors are used to monitor the
position of joints. Information about the
position is fed back to the control
systems that are used to determine the
accuracy of positioning.
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2. Range sensors:
Range sensors measure distances from a
reference point to other points of
importance. Range sensing is
accomplished by means of television
cameras or sonar transmitters and
receivers.
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3. Velocity Sensors:
They are used to estimate the speed with which
a manipulator is moved. The velocity is an
important part of the dynamic performance of the
manipulator. The DC tachometer is one of the
most commonly used devices for feedback of
velocity information. The tachometer, which is
essentially a DC generator, provides an output
voltage proportional to the angular velocity of the
armature. This information is fed back to the
controls for proper regulation of the motion.
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4. Proximity Sensors:
They are used to sense and indicate the
presence of an object within a specified
distance without any physical contact. This
helps prevent accidents and damage to
the robot.
– infra red sensors
– acoustic sensors
– touch sensors
– force sensors
– tactile sensors for more accurate data on the
position
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The Hand of a Robot: End-Effector
The end-effector (commonly known as
robot hand) mounted on the wrist enables
the robot to perform specified tasks.
Various types of end-effectors are
designed for the same robot to make it
more flexible and versatile. End-effectors
are categorized into two major types:
grippers and tools.
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The Hand of a Robot: End-Effector
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The Hand of a Robot: End-Effector
Grippers are generally used to grasp and
hold an object and place it at a desired
location.
– mechanical grippers
– vacuum or suction cups
– magnetic grippers
– adhesive grippers
– hooks, scoops, and so forth
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The Hand of a Robot: End-Effector
At times, a robot is required to manipulate
a tool to perform an operation on a
workpiece. In such applications the endeffector is a tool itself
– spot-welding tools
– arc-welding tools
– spray-painting nozzles
– rotating spindles for drilling
– rotating spindles for grinding
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Robot Movement and Precision
Speed of response and stability are two
important characteristics of robot
movement.
• Speed defines how quickly the robot arm
moves from one point to another.
• Stability refers to robot motion with the
least amount of oscillation. A good robot is
one that is fast enough but at the same
time has good stability.
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Robot Movement and Precision
Speed and stability are often conflicting
goals. However, a good controlling system
can be designed for the robot to facilitate a
good trade-off between the two
parameters.
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The precision of robot movement is defined
by three basic features:
1. Spatial resolution:
The spatial resolution of a robot is the
smallest increment of movement into
which the robot can divide its work
volume.
It depends on the system’s control
resolution and the robot's mechanical
inaccuracies.
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2. Accuracy: Accuracy can be defined as the
ability of a robot to position its wrist end at a
desired target point within its reach. In terms of
control resolution, the accuracy can be defined
as one-half of the control resolution. This
definition of accuracy applies in the worst case
when the target point is between two control
points.The reason is that displacements
smaller than one basic control resolution unit
(BCRU) can be neither programmed nor
measured and, on average, they account for
one-half BCRU.
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The accuracy of a robot is affected by
many factors. For example, when the arm
is fully stretched out, the mechanical
inaccuracies tend to be larger because the
loads tend to cause deflection.
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3. Repeatability: It is the ability of the robot
to position the end effector to the
previously positioned location.
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The Robotic Joints
A robot joint is a mechanism that permits
relative movement between parts of a
robot arm. The joints of a robot are
designed to enable the robot to move its
end-effector along a path from one
position to another as desired.
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The Robotic Joints
The basic movements required for a desired
motion of most industrial robots are:
• 1. rotational movement: This enables the robot
to place its arm in any direction on a horizontal
plane.
• 2. Radial movement: This enables the robot to
move its end-effector radially to reach distant
points.
• 3. Vertical movement: This enables the robot to
take its end-effector to different heights.
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The Robotic Joints
These degrees of freedom, independently
or in combination with others, define the
complete motion of the end-effector. These
motions are accomplished by movements
of individual joints of the robot arm. The
joint movements are basically the same as
relative motion of adjoining links.
Depending on the nature of this relative
motion, the joints are classified as
prismatic or revolute.
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The Robotic Joints
• Prismatic joints (L) are also known as
sliding as well as linear joints.
• They are called prismatic because the
cross section of the joint is considered as
a generalized prism. They permit links to
move in a linear relationship.
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The Robotic Joints
Revolute joints permit only angular
motion between links. Their variations
include:
– Rotational joint (R)
– Twisting joint (T)
– Revolving joint (V)
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The Robotic Joints
In a prismatic joint, also known as a
sliding or linear joint (L), the links are
generally parallel to one
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The Robotic Joints
A rotational joint (R) is identified by its
motion, rotation about an axis
perpendicular to the adjoining links. Here,
the lengths of adjoining links do not
change but the relative position of the links
with respect to one another changes as
the rotation takes place.
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The Robotic Joints
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The Robotic Joints
A twisting joint (T) is also a rotational
joint, where the rotation takes place about
an axis that is parallel to both adjoining
links.
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The Robotic Joints
A revolving joint (V) is another rotational
joint, where the rotation takes place about
an axis that is parallel to one of the
adjoining links. Usually, the links are
aligned perpendicular to one another at
this kind of joint. The rotation involves
revolution of one link about another.
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The Robotic Joints
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ROBOT CLASSIFICATION
Robots may be classified, based on:
– physical configuration
– control systems
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ROBOT CLASSIFICATION
Classification Based on Physical
Configuration:
– 1. Cartesian configuration
– 2. Cylindrical configuration
– 3. Polar configuration
– 4. Joint-arm configuration
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ROBOT CLASSIFICATION
Cartesian Configuration:
• Robots with Cartesian configurations
consists of links connected by linear joints
(L). Gantry robots are Cartesian robots
(LLL).
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Cartesian Robots
A robot with 3 prismatic joints
– the axes consistent with a
Cartesian coordinate system.
Commonly used for:
•pick and place work
•assembly operations
•handling machine tools
•arc welding
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Cartesian Robots
Advantages:
• ability to do straight line insertions into furnaces.
• easy computation and programming.
• most rigid structure for given length.
Disadvantages:
• requires large operating volume.
• exposed guiding surfaces require covering in corrosive
or dusty environments.
• can only reach front of itself
• axes hard to seal
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ROBOT CLASSIFICATION
Cylindrical Configuration:
• Robots with cylindrical configuration have
one rotary ( R) joint at the base and linear
(L) joints succeeded to connect the links.
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Cylindrical Robots
A robot with 2 prismatic joints
and a rotary joint – the axes
consistent with a cylindrical
coordinate system.
Commonly used for:
•handling at die-casting
machines
•assembly operations
•handling machine tools
•spot welding
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Cylindrical Robots
Advantages:
• can reach all around itself
• rotational axis easy to seal
• relatively easy programming
• rigid enough to handle heavy loads through large working
space
• good access into cavities and machine openings
Disadvantages:
• can't reach above itself
• linear axes is hard to seal
• won’t reach around obstacles
• exposed drives are difficult to cover from dust and liquids
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ROBOT CLASSIFICATION
Polar Configuration:
• Polar robots have a
work space of
spherical shape.
Generally, the arm is
connected to the
base with a twisting
(T) joint and rotatory
(R) and linear (L)
joints follow.
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ROBOT CLASSIFICATION
• The designation of the arm for this
configuration can be TRL or TRR.
• Robots with the designation TRL are also
called spherical robots. Those with the
designation TRR are also called
articulated robots. An articulated robot
more closely resembles the human arm.
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ROBOT CLASSIFICATION
Joint-arm Configuration:
• The jointed-arm is a combination of
cylindrical and articulated configurations.
The arm of the robot is connected to the
base with a twisting joint. The links in the
arm are connected by rotatory joints. Many
commercially available robots have this
configuration.
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ROBOT CLASSIFICATION
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Articulated Robots
A robot with at least 3 rotary
joints.
Commonly used for:
•assembly operations
•welding
•weld sealing
•spray painting
•handling at die casting or
fettling machines
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Articulated Robots
Advantages:
• all rotary joints allows for maximum flexibility
• any point in total volume can be reached.
• all joints can be sealed from the environment.
Disadvantages:
• extremely difficult to visualize, control, and program.
• restricted volume coverage.
• low accuracy
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SCARA (Selective Compliance
Articulated Robot Arm) Robots
A robot with at least 2 parallel
rotary joints.
Commonly used for:
•pick and place work
•assembly operations
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SCARA (Selective Compliance
Articulated Robot Arm) Robots
Advantages:
• high speed.
• height axis is rigid
• large work area for floor space
• moderately easy to program.
Disadvantages:
• limited applications.
• 2 ways to reach point
• difficult to program off-line
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• highly complex arm
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Spherical/Polar Robots
A robot with 1 prismatic joint
and 2 rotary joints – the axes
consistent with a polar
coordinate system.
Commonly used for:
•handling at die casting or
fettling machines
•handling machine tools
•arc/spot welding
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Spherical/Polar Robots
Advantages:
• large working envelope.
• two rotary drives are easily sealed against liquids/dust.
Disadvantages:
• complex coordinates more difficult to visualize, control,
and program.
• exposed linear drive.
• low accuracy.
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ROBOT CLASSIFICATION
Classification Based on Control Systems:
– 1. Point-to-point (PTP) control robot
– 2. Continuous-path (CP) control robot
– 3. Controlled-path robot
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Point to Point Control Robot (PTP):
• The PTP robot is capable of moving from one
point to another point.
• The locations are recorded in the control
memory. PTP robots do not control the path to
get from one point to the next point.
• Common applications include:
–
–
–
–
–
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component insertion
spot welding
hole drilling
machine loading and unloading
assembly operations
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Continuous-Path Control Robot (CP):
• The CP robot is capable of performing movements along
the controlled path. With CP from one control, the robot
can stop at any specified point along the controlled path.
• All the points along the path must be stored explicitly in
the robot's control memory. Applications Straight-line
motion is the simplest example for this type of robot.
Some continuous-path controlled robots also have the
capability to follow a smooth curve path that has been
defined by the programmer. In such cases the
programmer manually moves the robot arm through the
desired path and the controller unit stores a large
number of individual point locations along the path in
memory (teach-in).
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Continuous-Path Control Robot (CP):
Typical applications include:
– spray painting
– finishing
– gluing
– arc welding operations
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Controlled-Path Robot:
• In controlled-path robots, the control equipment can
generate paths of different geometry such as straight
lines, circles, and interpolated curves with a high degree
of accuracy. Good accuracy can be obtained at any point
along the specified path.
• Only the start and finish points and the path definition
function must be stored in the robot's control memory. It
is important to mention that all controlled-path robots
have a servo capability to correct their path.
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Robot Reach:
Robot reach, also known as the work
envelope or work volume, is the space of
all points in the surrounding space that
can be reached by the robot arm.
Reach is one of the most important
characteristics to be considered in
selecting a suitable robot because the
application space should not fall out of the
selected robot's reach.
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Robot Reach:
• For a Cartesian configuration the reach is
a rectangular-type space.
• For a cylindrical configuration the reach is
a hollow cylindrical space.
• For a polar configuration the reach is part
of a hollow spherical shape.
• Robot reach for a jointed-arm
configuration does not have a specific
shape.
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ROBOT MOTION ANALYSIS
In robot motion analysis we study the
geometry of the robot arm with respect to
a reference coordinate system, while the
end-effector moves along the prescribed
path .
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ROBOT MOTION ANALYSIS
The kinematic analysis involves two
different kinds of problems:
– 1. Determining the coordinates of the endeffector or end of arm for a given set of joints
coordinates.
– 2. Determining the joints coordinates for a
given location of the end-effector or end of
arm.
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ROBOT MOTION ANALYSIS
The position, V, of the end-effector can be
defined in the Cartesian coordinate
system, as:
V = (x, y)
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ROBOT MOTION ANALYSIS
Generally, for robots the location of the
end-effector can be defined in two
systems:
a. joint space and
b. world space (also known as global
space)
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ROBOT MOTION ANALYSIS
In joint space, the joint parameters such
as rotating or twisting joint angles and
variable link lengths are used to represent
the position of the end-effector.
– Vj = (q, a)
– Vj = (L1, , L2)
– Vj = (a, L2)
for RR robot
for LL robot
for TL robot
where Vj refers to the position of the endeffector in joint space.
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ROBOT MOTION ANALYSIS
In world space, rectilinear coordinates
with reference to the basic Cartesian
system are used to define the position of
the end-effector.
Usually the origin of the Cartesian axes is
located in the robot's base.
– VW = (x, y)
where VW refers to the position of the endeffector in world space.
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ROBOT MOTION ANALYSIS
• The transformation of coordinates of the
end-effector point from the joint space to
the world space is known as forward
kinematic transformation.
• Similarly, the transformation of coordinates
from world space to joint space is known
as backward or reverse kinematic
transformation.
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Forward KinematicTransformation
LL Robot:
Let us consider a Cartesian LL robot
J 1( x 1 , y1)
y
L
2
J 2 ( x 2 ,y 2 )
L
( x ,
L
3
Joints J1 and J2 are linear joints
with links of variable lengths L1 and
L2. Let joint J1 be denoted by (x1
y1) and joint J2 by (x2, y2).
From geometry, we can easily get
the following:
y )
x2=x1+L2
1
y2 = y1
x
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Forward KinematicTransformation
These relations can be represented in homogeneous matrix
form:
x2   1 0 L2  x1
y2   0 1 0   y1
 1  0 0 1   1 
or
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X2=T1 X1
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Forward KinematicTransformation
where
 x2 
X2   y 2 
 1
 1 0 L2 
T1  0 1 0 
0 0 1 
x1
X1y1
 1
If the end-effector point is denoted by (x, y), then:
x = x2
y = y2 - L3
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Forward KinematicTransformation
therefore:
 x   1 0 0   x2 
y   0 1 L2   y2 
 1  0 0 1   1 
X = T2 X2
or
and
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TLL = T2 T1
 1 0 L2 
TLL  0 1 L 
0 0 1 
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Forward KinematicTransformation
RR Robot:
Let q and a be the rotations at joints J1 and J2
respectively. Let J1 and J2 have the coordinates of (x1,
y1) and (x2, y2), respectively.
One can write the following
from the geometry:
x2 = x1+L2 cos(q)
y2 = y1 +L2 sin(q)
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Forward KinematicTransformation
In matrix form:
x2   1 0 L2 cos(q) x1
y2   0 1 L2 sin(q)   y1
1   1
 1  0 0
or
X2 = T1 X1
On the other end:
x = x2 +L3 cos(a-q)
y = y2 - L3 sin(a-q)
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Forward KinematicTransformation
In matrix form:
x  1 0 L2 cos(a  q)  x2 
y  0 1 L2 sin(a  q)  y2 
1
1 0 0
  1
or
X = T2 X2
Combining the two equation gives:
X = T2 (T1 X1) = TRR X1
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Forward KinematicTransformation
where
TRR = T2 T1
 1 0 L2 cos(q)  L2 cos(a  q)
TRR  0 1 L2 sin(q)  L2 sin(a  q) 
1
0 0

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Forward KinematicTransformation
TL Robot:
Let a be the rotation at twisting joint J1 and L2 be the
variable link length at linear joint J2.
z
J
2
( x
2
y
y 2 )
One can write that:
( x
L
J1
( x 1
y
)
x = x2 + L2 cos(a)
2
y
1 )
y = y2 + L2 sin(a)
x
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Forward KinematicTransformation
In matrix form:
x  1 0 L2 cos(a) x2 
y  0 1 L2 sin(a)   y2 
1
1 0 0
  1
or
X = TTL X2
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Backward Kinematic Transformation
LL Robot:
In backward kinematic transformation, the objective is to
drive the variable link lengths from the known position of
the end effector in world space.
x = x1 + L2
y = y1 - L3
y1 = y2
By combining above equations, one can get:
L2 = x - x1
L3 = -y +y2
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Backward Kinematic Transformation
RR Robot:
x = x1 + L2 cos(q) + L3 cos(a-q)
y = y1 + L2 sin(q) - L3 sin(a-q)
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Backward Kinematic Transformation
One can easily get the angles:


x - x   y  y   L  L 
cos (a ) =
2
1
2
1
2
2
2
3
2 L 2 L3
and

y - y1 L2  L3 cos(a )    x  x1  L3 sin( a )
tan(q ) =
x - x1 L2  L3 cos(a )    y  y1  L3 sin( a )
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Backward Kinematic Transformation
TL Robot:
x = x2 + L cos(a)
y = y2 +L sin(a)
One can easily get the equations for length and angle:
L=
x - x 2   y  y 2 
2
2
and
y - y2
sin(a) =
L
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EXAMPLE
An LL robot has two links of variable length.
Assuming that the origin of the global coordinate
system is defined at joint J1, determine the
following:
a)The coordinate of the end-effector point if the
variable link lengths are 3m and 5 m.
b) Variable link lengths if the end-effector is
located at (3, 5).
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EXAMPLE
J 1( 0 , 0 )
x
L
2
=
3
m
J 2 ( x 2 ,y 2 )
L
( x ,
L
=
3
5
m
y )
1
y
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EXAMPLE
Solution:
a) It is given that:
(x1, y1) = (0, 0)
 1 0 L2 
TLL  0 1 L3 
0 0 1 
1 0 3 
TLL  0 1 5
0 0 1 
 x
x1
y  TLLy1
 1
 1
Therefore the endeffector point is given
by (3, -5).
x  1 0 3 0
y  0 1 50
1 0 0 1  1
 x  3 
y  5
 1  1 
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EXAMPLE
b) The end effector point is given by (3, 5)
Then:
L2 = x - x1 = 3 - 0 = 3 m
L3 = -y + y1 = -5 + 0 = -5 m
( 3 ,
L
The variable lengths
are 3 m and 5 m. The
minus sign is due to
the coordinate system
used.
J 1( 0 , 0 )
5 )
3
L
2
x
J 2 ( x 2 ,y 2 )
L
1
y
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EXAMPLE
An RR robot has two links of length 1 m. Assume that the origin of
the global coordinate system is at J1.
a) Determine the coordinate of the end-effector point if the joint
rotations are 30o at both joints.
b) Determine joint rotations if the end-effector is located at (1, 0)
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EXAMPLE
It is given that (x1, y1) = (0, 0)
 1 0 L2 cos(q)  L2 cos(a  q)
TRR  0 1 L2 sin(q)  L2 sin(a  q) 
1
0 0

Therefore the end-effector point
is given by (1.8667, 0.5)


1 0 3 1


2
TRR  0 1 1  0 
2


0
0
1




 x
x1
 y = TRRy1
 1
1
 x  1 0 18667
.
0
 y  0 1 0.5 0
1  1
1 0 0
 x 18667
.

 y   0.5 
1  0.51 
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EXAMPLE
2004
115
EXAMPLE
It is given that (x, y) = (1, 0), therefore,
x 2  y 2  L22  L23
cos(a ) =
2 L3 L2
12  0 2  12  12
cos(a ) =
 0.5
2 x1x1
a = 120o
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EXAMPLE

y - y1 L2  L3 cos(a )    x  x1  L3 sin( a )
tan(q ) =
x - x1 L2  L3 cos(a )    y  y1  L3 sin( a )

0 - 01  1x cos(120)   1  01 sin( 120)
tan(q ) =
1 - 01  1cos(120)   0  01 sin( 120)
3
tan(q) = 2 = 3
0.5
q = 60o
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EXAMPLE
In a TL robot, assume that the coordinate system is
defined at joints J2.
a) Determine the coordinates of the end-effector point
if joint J1 twist by an angle of 30o and the variable link
has a length of 1 m.
b) Determine variable link length and angle of twist at
J1 if the end-effector is located at (0.7071, 0.7071)
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EXAMPLE
z
J
2
( 0
0
y
)
( x
L
J1
( x 1
2
y
= 1
y
)
m
1 )
x
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EXAMPLE
a) It is given that (x2, y2) = (0, 0); L = 1m and a = 30o
1 0 L2 cos(a )
TTL  0 1 L2 sin( a ) 
0 0

1
2004
TTL
1 0 1 cos(30 o )


 0 1 1sin( 30 o ) 
0 0

1


TTL
1 0 0.866
 0 1 0.5 
0 0
1 
120
EXAMPLE
 x  1 0 0.866 0
 y    0 1 0. 5    0 
  
  
 1  0 0
1  1
 x  0.866
 y    0. 5 
  

 1   1 
(x, y) = (0.866, 0.5)
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EXAMPLE
b)It is given that (x, y) = (0.7071, 0.7071)
L = (x - x1 ) 2  ( y  y1 ) 2
L = (0.7071 - 0) 2  (0.7071  0) 2
L 1m
sin(a) = (y-y2)/L = (0.7071-0)/1 = 0.7071
a = 45o
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Where Used and Applied
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ROBOT APPLICATIONS
Loading/unloading parts to/from the machines
– The robot unloading parts from die-casting machines
– The robot loading a raw hot billet into a die, holding it
during forging and unloading it from the forging die
– The robot loading sheet blanks into automatic
presses
– The robot unloading molded parts formed in injection
molding machines
– The robot loading raw blanks into NC machine tools
and unloading the finished parts from the machines
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ROBOT APPLICATIONS
Welding
– Spot welding: Widest use is in the automotive industry
– Arc welding: Ship building, aerospace, construction industries are
among the many areas of application.
Spray painting:
Provides a consistency in paint quality. Widely used in automobile
industry.
Assembly:
Electronic component assemblies and machine assemblies are two
areas of application.
Inspection
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ECONOMIC JUSTIFICATION OF ROBOTS
Payback period method:
net investment cost of the robot system including accesories
n
net annual cash flow
n = number of years that the investment is paid back
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126
ECONOMIC JUSTIFICATION OF ROBOTS
net investment cost = total investment cost
of robot - investment tax
credit
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127
ECONOMIC JUSTIFICATION OF ROBOTS
net annual cash flow = annual anticipated revenues
from robot installation including
direct labor and material cost
savings – annual operating
costs including labor, material
and maintenance costs of the
robot system
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ECONOMIC JUSTIFICATION OF ROBOTS
EXAMPLE: A company is planning to replace a manual
painting system by a robotic system. The system is
priced at $160,000 which includes sensors, grippers and
other required accessories. The annual maintenance
and operation cost of robot system on a single-shift basis
is $10,000. The company is eligible for a $20,000 tax
credit from the government under its technology
investment program. The robot will replece two
operators. The hourly rate of an operator is $20 including
fringe benefits. There is no increase in production rate.
Determine the payback period for one-shift and two-shift
operations.
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ECONOMIC JUSTIFICATION OF ROBOTS
Net investment cost = capital cost – tax credits
Net investment cost = 160,000 [$]- 20,000 [$]
= 140,000 [$]
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130
ECONOMIC JUSTIFICATION OF ROBOTS
Annual labor cost = operator rate x number
of operators x days per
x hours per day
Annual labor cost = 20 [$/hr] x 2 x 250 [d/yr] x 8 [hr/d]
Annual labor cost = 80,000 [$/yr] (for a single shift)
Annual labor cost = 160,000 [$/yr] (for a double shift)
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ECONOMIC JUSTIFICATION OF ROBOTS
Annual saving = annual labor cost – annual
maintenance and operating cost
Annual saving = 80,000 [$/yr] - 10,000 [$/yr]
= $70,000 [$/yr] (for a single shift)
Annual saving = 160,000 [$/yr] - 20,000 [$/yr]
= $140,000 [$/yr] (for a double shift)
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ECONOMIC JUSTIFICATION OF ROBOTS
for a single shift:
Payback period = 140,000 [$] / 70,000 [$/yr] = 2 [yr]
for a double shift:
Payback period = 140,000 [$] / 140,000 [$/yr] = 1 [yr]
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ECONOMIC JUSTIFICATION OF ROBOTS
EXAMPLE:
• Compute the cycle time and production rate for a single machine robotic cell
for an 8 hour shift if the system availability is 90%. Also determine the
percent utilization of machine and robot.
• Machine processing time
30 s
• Robot picks up the part from the conveyor
3.0 s
• Robot moves the part to the machine
1.3 s
• Robot loads the part on to the machine
1.0 s
• Robot unloads the part from the machine
0.7 s
• Robot moves the part to the conveyor
1.5 s
• Robot puts the part on to the outgoing
• conveyor
0.5 s
• Robot moves from the output conveyor
• to the input conveyor
4.0 s
•
2004
Total
12 s
134
ECONOMIC JUSTIFICATION OF ROBOTS
Solution:
• The total cycle time: 30 + 12 = 42 s
Production rate:
• (1/42) part/s 3600 s/hr 8 hr/shift 0.90 (uptime)
• = 617 parts/shift
Machine utilization:
• Machine cycle time/total cycle time = 30/42
• = 71.4%
Robot utilization:
• robot cycle time/total cycle time : 12/42
• = 28.6%
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Advantages
• Greater flexibility, re-programmability
• Greater response time to inputs than humans
• Improved product quality
• Maximize capital intensive equipment in multiple work
shifts
• Accident reduction
• Reduction of hazardous exposure for human workers
• Automation less susceptible to work stoppages
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Disadvantages
•Replacement of human labor
• Greater unemployment
• Significant retraining costs
users of new technology
for
both
unemployed
and
• Advertised technology does not always disclose some of the
hidden disadvantages
• Hidden costs because of the associated technology that must
be purchased and integrated into a functioning cell. Typically, a
functioning cell will cost 3-10 times the cost of the robot.
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Limitations
•Assembly dexterity does not match that of human beings,
particularly where eye-hand coordination required.
• Payload to robot weight ratio is poor, often less than 5%.
• Robot structural configuration may limit joint movement.
• Work volumes can be constrained
tooling/sensors added to the robot.
by
parts
or
• Robot repeatability/accuracy can constrain the range of
potential applications.
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ROBOT SELECTION
In a survey published in 1986, it is stated that there are 676
robot models available in the market. Once the application is
selected, which is the prime objective, a suitable robot should
be chosen from the many commercial robots available in the
market.
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ROBOT SELECTION
The characteristics of robots generally considered in a selection process include:
Size of class
Degrees of freedom
Velocity
Drive type
Control mode
Repeatability
Lift capacity
Right-left traverse
Up-down traverse
In-out traverse
Yaw
Pitch
Roll
Weight of the robot
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ROBOT SELECTION
1. Size of class: The size of the robot is given by the
maximum dimension (x) of the robot work envelope.
Micro (x < 1 m)
Small (1 m < x < 2 m)
Medium (2 < x < 5 m)
Large (x > 5 m)
2. Degrees of freedom. The cost of the robot increases with
the number of degrees of freedom. Six degrees of freedom is
suitable for most works.
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ROBOT SELECTION
3. Velocity: Velocity consideration is effected by the robot’s
arm structure.
Rectangular
Cylindrical
Spherical
Articulated
4. Drive type:
Hydraulic
Electric
Pneumatic
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ROBOT SELECTION
5. Control mode:
Point-to-point control(PTP)
Continuous path control(CP)
Controlled path control
6. Lift capacity:
0-5 kg
5-20 kg
20-40 kg and so forth
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