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MIDDLE EAST TECHNICAL UNIVERSITY Mechanical Engineering Department

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Title: MIDDLE EAST TECHNICAL UNIVERSITY Mechanical Engineering Department


1
MIDDLE EAST TECHNICAL UNIVERSITYMechanical
Engineering Department
ME 445 Integrated Manufacturing Systems
2
ROBOTICS
3
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
4
Robotics Terminology
Robotics The science of robots. Humans working
in this area are called roboticists.
5
Robotics Terminology
DOF degrees-of-freedom the number of independent
motions a device can make. (Also called mobility)
five degrees of freedom
6
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.
7
Robotics Terminology
End-effector The tool, gripper, or other device
mounted at the end of a manipulator, for
accomplishing useful tasks.
8
Robotics Terminology
Workspace The volume in space that a robots
end-effector can reach, both in position and
orientation.
A cylindrical robots half workspace
9
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
10
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.
11
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.

12
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.

13
Robotics Terminology
14
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.
15
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.
16
Robotics History
Leonardos Robot
17
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.
18
Robotics History
Joseph Jacquards Automated Loom
19
Robotics History
1898 Nikola Tesla builds and demonstrates a
remote controlled robot boat.
20
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.
21
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.

22
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.
23
Robotics History
SRI Shakey
Unimate PUMA
24
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.
25
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.
26
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.
27
Robotics History
1996 Honda debuts the P3.
28
Robotics History
1997 The Pathfinder Mission lands on Mars
1999 SONY releases the AIBO robotic pet.
29
Robotics History
2000 Honda debuts new humanoid robot ASIMO.
30
Industrial Robots
31
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.

32
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

33
  • 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

34
  • 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

35
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

36
  • 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.

37
  • 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.

38
  • 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.

39
  • 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

40
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.

41
The Hand of a Robot End-Effector
42
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

43
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

44
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.

45
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.

46
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.

47
  • 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.

48
  • 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.

49
  • 3. Repeatability It is the ability of the robot
    to position the end effector to the previously
    positioned location.

50
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.

51
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.

52
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.

53
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.

54
The Robotic Joints
  • Revolute joints permit only angular motion
    between links. Their variations include
  • Rotational joint (R)
  • Twisting joint (T)
  • Revolving joint (V)

55
The Robotic Joints
  • In a prismatic joint, also known as a sliding or
    linear joint (L), the links are generally
    parallel to one

56
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.

57
The Robotic Joints
58
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.

59
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.

60
The Robotic Joints
61
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62
ROBOT CLASSIFICATION
  • Robots may be classified, based on
  • physical configuration
  • control systems

63
ROBOT CLASSIFICATION
  • Classification Based on Physical Configuration
  • 1. Cartesian configuration
  • 2. Cylindrical configuration
  • 3. Polar configuration
  • 4. Joint-arm configuration

64
ROBOT CLASSIFICATION
  • Cartesian Configuration
  • Robots with Cartesian configurations consists of
    links connected by linear joints (L). Gantry
    robots are Cartesian robots (LLL).

65
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

66
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

67
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.

68
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

69
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

70
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.

71
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.

72
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.

73
ROBOT CLASSIFICATION
74
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

75
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

76
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

77
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

78
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

79
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.

80
ROBOT CLASSIFICATION
  • Classification Based on Control Systems
  • 1. Point-to-point (PTP) control robot
  • 2. Continuous-path (CP) control robot
  • 3. Controlled-path robot

81
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

82
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).

83
Continuous-Path Control Robot (CP)
  • Typical applications include
  • spray painting
  • finishing
  • gluing
  • arc welding operations

84
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.

85
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.

86
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.

87
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88
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 .

89
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.

90
ROBOT MOTION ANALYSIS
  • The position, V, of the end-effector can be
    defined in the Cartesian coordinate system, as
  • V (x, y)

91
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)

92
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.

93
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.

94
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.

95
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
96
Forward KinematicTransformation
  • These relations can be represented in
    homogeneous matrix form

or
X2T1 X1
97
Forward KinematicTransformation
  • where

If the end-effector point is denoted by (x, y),
then
x x2 y y2 - L3
98
Forward KinematicTransformation
  • therefore

X T2 X2
or
TLL T2 T1
and
99
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)
100
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)
101
Forward KinematicTransformation
  • In matrix form

or X T2 X2 Combining the two equation
gives X T2 (T1 X1) TRR X1
102
Forward KinematicTransformation
  • where
  • TRR T2 T1

103
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)
104
Forward KinematicTransformation
  • In matrix form

or X TTL X2
105
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

106
Backward Kinematic Transformation
  • RR Robot
  • x x1 L2 cos(q) L3 cos(a-q)
  • y y1 L2 sin(q) - L3 sin(a-q)

107
Backward Kinematic Transformation
One can easily get the angles
  • and

108
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

109
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).

110
EXAMPLE
111
EXAMPLE
  • Solution
  • It is given that
  • (x1, y1) (0, 0)

Therefore the end-effector point is given by (3,
-5).
112
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.
113
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)

114
EXAMPLE
  • It is given that (x1, y1) (0, 0)

Therefore the end-effector point is given by
(1.8667, 0.5)
115
EXAMPLE
116
EXAMPLE
  • It is given that (x, y) (1, 0), therefore,

117
EXAMPLE
118
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
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