MIDDLE EAST TECHNICAL UNIVERSITY Mechanical Engineering Department

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MIDDLE EAST TECHNICAL UNIVERSITYMechanical
Engineering Department
ME 445 Integrated Manufacturing Systems
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ROBOTICS
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Robotics Terminology
Robot An electromechanical device with multiple
degrees-of-freedom (DOF) that is programmable to
accomplish a variety of tasks.
Industrial robotThe Robotics Industries
Association (RIA) defines robot in the following
way An industrial robot is a programmable,
multi-functional 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, 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 robots
end-effector can reach, both in position and
orientation.
A cylindrical robots half workspace
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Robotics Terminology
Position The translational (straight-line)
location of something. Orientation The
rotational (angle) location of something. A
robots 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.
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 designs water clocks that have movable
figures on them.
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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
Leonardos 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 controlled with punched
cards.
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Robotics History
Joseph Jacquards 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 Robotics.
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Robotics History

• Three Laws of Robotics
• A robot may not injure a human being, or, through
  inaction, allow a human being to come to harm.
• A robot must obey the orders given it by human
  beings except where such orders would conflict
  with the First Law.
• 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
SRI Shakey
Unimate PUMA
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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
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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• 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 end-effector 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

• 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 systems 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
• wont 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
• 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
• 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
  end-effector 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) for RR robot
• Vj (L1, , L2) for LL robot
• Vj (a, L2) for TL robot
• where Vj refers to the position of the
  end-effector 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
  end-effector 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

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
x2x1L2 y2 y1
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Forward KinematicTransformation

• These relations can be represented in
  homogeneous matrix form

or
X2T1 X1
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Forward KinematicTransformation

• where

If the end-effector point is denoted by (x, y),
then
x x2 y y2 - L3
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Forward KinematicTransformation

• therefore

X T2 X2
or
TLL T2 T1
and
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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 x1L2 cos(q) y2 y1 L2 sin(q)
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Forward KinematicTransformation

• In matrix form

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

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

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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.

One can write that x x2 L2 cos(a) y y2
L2 sin(a)
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Forward KinematicTransformation

• In matrix form

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

• and

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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

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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
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EXAMPLE

• Solution
• It is given that
• (x1, y1) (0, 0)

Therefore the end-effector point is given by (3,
-5).
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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

The variable lengths are 3 m and 5 m. The minus
sign is due to the coordinate system used.
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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)

Therefore the end-effector point is given by
(1.8667, 0.5)
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EXAMPLE
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EXAMPLE

• It is given that (x, y) (1, 0), therefore,

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EXAMPLE
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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)

119
EXAMPLE
120
EXAMPLE

• a) It is given that (x2, y2) (0, 0) L 1m
  and a 30o

121
EXAMPLE

• (x, y) (0.866, 0.5)

122
EXAMPLE

• b)It is given that (x, y) (0.7071, 0.7071)

sin(a) (y-y2)/L (0.7071-0)/1 0.7071 a 45o
123
Where Used and Applied
124
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

125
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

126
ECONOMIC JUSTIFICATION OF ROBOTS

• Payback period method

n number of years that the investment is paid
back
127
ECONOMIC JUSTIFICATION OF ROBOTS

• net investment cost total investment cost
  of robot - investment tax credit

128
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

129
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.

130
ECONOMIC JUSTIFICATION OF ROBOTS

• Net investment cost capital cost tax credits

Net investment cost 160,000 - 20,000
140,000
131
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)
132
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)
133
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

134
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
• Total 12 s

135
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

136
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

137
Disadvantages

• Replacement of human labor
• Greater unemployment
• Significant retraining costs for both unemployed
  and users of new technology
• 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.

138
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 by parts or
  tooling/sensors added to the robot.
• Robot repeatability/accuracy can constrain the
  range of potential applications.

139
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.
140
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
141
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 lt 1 m) Small (1 m lt x lt 2
m) Medium (2 lt x lt 5 m) Large (x gt 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.
142
ROBOT SELECTION
3. Velocity Velocity consideration is effected
by the robots arm structure. Rectangular Cylin
drical Spherical Articulated 4. Drive type
Hydraulic Electric Pneumatic
143
ROBOT SELECTION
5. Control mode Point-to-point
control(PTP) Continuous path control(CP) Control
led path control 6. Lift capacity 0-5
kg 5-20 kg 20-40 kg and so forth