CEN-458
ROBOTICS
Dr. ABDUL ATTAYYAB KHAN
EMAIL ADDRESS:
aakhan.bukc@bahria.edu.pk
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1
Introduction
What is Robot
 Definition:(no precise definition)
— Webster’s Dictionary
•
—
An automatic device that performs functions ordinarily ascribed to human
beings.
Robotics Institute of American
•
A robot (industrial robot) is a reprogrammable, multifunctional manipulator
designed to move materials, parts, tools, or specialized devices through variable
program motions for the performance of a variety of tasks.
Autonomous – able to act on its own, make decisions without control by human
Exists in the physical world
Sense its environment – robot include devices that provide sensory input.
Can take action in response – robots can take action to affect the physical world,
based on inputs from sensors and its internal programming.
Achieve goals -- robots are design for a purpose or can be directed to achieve
goals.
A robot is an autonomous system which exists in the physical world, can
sense its environment, and can act on it to achieve some goals.
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What is Robot
 Primitives of robotics are:
 A robot must be:
— Autonomous: able to act on its own, make decisions without
control by human.
― Exists in real world
― Sense its environment: robots include devices that provides
sensory input. Autonomous robots require input from sensors in
order to make decision.
― Can take action in response: robots can take action to affect the
physical world, based on input from the sensors and its
programming.
A robot is an autonomous system which exists in the physical world,
can sense its environment, and can act on it to achieve some goals.
Why use Robot

To qualify as a robot, a machine must be able to:
1.
Sensing and perception: get information from its surroundings
2. Carry out different tasks: Locomotion or manipulation, do
something physical, such as move or manipulate objects.
3. Re-programmable: can do different things.
4. Function autonomously and/or interact with human.
 A robot:
― Increase product quality
― Superior accuracy
― Increase efficiency
― Increase productivity
― Reduce cost
― Reduce time
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Why use Robot
 Domain of operation
― Robots can be designed and built for any environment imaginable. One
popular way of classifying robots is by what environment they are
designed to operate in. Some typical examples include:
• Stationary: fixed in one place and cannot move.
This category includes robotic arms.
• Ground: designed to operate on the surface of the earth
• Underwater: autonomous underwater vehicle.
• Aerial: Unmanned aerial vehicles
What is Industrial Robot

Industrial robot
― serves as a general purpose skilled or semiskilled laborer.
Western Europe
Japan
USA
others
4
What is Industrial Robot
Industrial robot

Types of Robot
•
Robot manipulator
•
Mobile Manipulator
• Locomotion
5
Components & Structure of Robots
Components & Structure of Robots
 Mechanisms might be used to provide such functions as:
1. Force amplification, e.g. that given by levers.
2. Change of speed, e.g. that given by gears.
3. Transfer of rotation about one axis to rotation about another, e.g. a timing
belt.
4. Particular types of motion, e.g. that given by a quick-return mechanism.
 The term kinematics is used for the study of motion without regards to forces.
 When we consider just the motions without any consideration of the forces or
energy involved then we are carrying out kinematic analysis of the mechanism.
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Components & Structure of Robots
 A rigid body can have a very complex motion which might seen difficult to describe.
 However, the motion of any rigid body can be considered to be a combination of
translational and rotational motions.

By considering the three dimensions the three dimensions of space, a translation
motion can be considered to be a movement which can be resolved into components
alone one or more of the three axes figure 1(a).
 A rotation can be considered as a rotation which has components rotating about one
or more of the axes figure 1(b).
(a)
(b)
Figure 1: Type of Motions
Components & Structure of Robots
 A complex motion may be a combination of translational and rotational motions.
 For example, think of the motion required to pick up a pencil from a table.
 This might involve hand moving at a particular angle towards the table, rotation of the
hand, and then all the movement associated with opening your fingers and moving
them to the required positions to grasp the pencil.
 This is a sequence of quite complex motions. However, we can break down all these
motions into combinations of translational and rotational motions.
 Such an analysis is particularly relevant if we are not moving a human hand to pick up
the pencil but instructing a robot to carry out the task.
 Then it really is necessary to break down the motion into combinations of translational
and rotational motions so that we can design mechanisms to carry out each of these
components of the motion.
 For example, among the sequence of control signals sent to a mechanism might be such
groupings of signals as those to instruct joint 1 to rotate by 20 and link 2 to be
extended by 4mm for translational motion.
7
Types of Joints in Industrial Robotic

Two types of joints used in industrial robotics:
1) Revolute joints: rotation about a single axis
— Parallel to link
— Perpendicular to link
2) Prismatic joints: sliding along a single axis
3) Other joint types:
― Cylindrical (sliding and turning)
― Screw (helical motion)
― Flexible
― Spherical
Components & Structure of Robots
 Robot Manipulators: are composed of links connected by joints
to form a kinematic chain.
 Joints: are typically rotary (revolute) or linear (prismatic).
 A revolute joint is like a hinge and allows relative rotation
between two links.
 Prismatic joint: allows a linear relative motion
between two links.
 Revolute joints: are denoted by R
 Prismatic joints: are denoted by P
 Robot manipulator: with n joints will have
(n + 1) links. Each joint connects two links.
Figure 2: Robot Manipulator
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Mathematical Modelling of Robots
 While robots are themselves mechanical systems, we will be primarily concerned
with developing and manipulating mathematical models for robots.
 In particular, we will develop methods to represent basic geometric aspects of
robotic manipulation, dynamic aspects of manipulation, and the various sensors
available in modern robotic systems.
 Equipped with these mathematical models, we will be able to develop methods for
planning and controlling robot motions to perform specified tasks.
 We describe some of the basic ideas that are common in developing mathematical
models for robot manipulators.
Mathematical Modelling of Robots
Symbolic Representation of Robots:

Robot Manipulators are composed of links connected by joints to form a
kinematic chain.

Joints are typically rotary (revolute) or linear (prismatic).

A revolute joint is like a hinge and allows relative rotation between two links.

A prismatic joint allows a linear relative motion between two links.

We denote revolute joints by R and prismatic joint by P, and draw them as
shown in Figure 3.
Figure 3: Symbolic representation of robot joints
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Mathematical Modelling of Robots
Symbolic Representation of Robots:

For example, a three-link arm with three revolute joints is an RRR arm.

Each joint represents the interconnection between two links.

We denote the axis of rotation of a revolute joint, or the axis along which a
prismatic joints translates by
if the joint is the interconnection of links and
+ .

The joint variables, denoted by
for a revolute joint and
for the prismatic
joint, represent the relative displacement between adjacent links.
Mathematical Modelling of Robots
The Configuration Space:

A configuration of a manipulator is a complete specification of the location of
every point on the manipulator.

The set of all possible configurations is called the configuration space.

If we know the values for the joint variables (i.e., the joint angle for revolute
joints, or the joint offset for prismatic joint), then it is straightforward to
infer the position of any point on the manipulator, since the individual links of
the manipulator is assumed to be rigid, and the base of the manipulator is
assumed to be fixed.

Therefore, the configuration can be represented by a set of values for the joint
variables.

We will denote this vector of values by
, and say that the robot is in
configuration when the joint variables take on the values
… , with
=
=
for a revolute joint and
for a prismatic joint.
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Mathematical Modelling of Robots
The Configuration Space:
 An object is said to have
degrees-of-freedom (DOF) if its
configuration can be minimally specified by
parameters.
 Thus, the number of DOF is equal to the dimension of the configuration
space.
 For a robot manipulator, the number of joints determines the number
of DOF.
 A
rigid object in three-dimensional space has six DOF: three
positioning and three for orientation (e.g., roll, pitch and yaw
angles.
 Therefore,
a manipulator
independent DOF.
should
typically
possess
at
least
six
Mathematical Modelling of Robots
The Configuration Space:
 With fewer than six DOF the arm cannot reach every point in its work
environment with arbitrary orientation.
 Certain applications such as reaching around or behind obstacles may
require more than six DOF.
 A manipulator having more than six links is
referred to as a
kinematically redundant manipulator.
 The difficulty of controlling a manipulator increases rapidly with the
number of links.
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Mathematical Modelling of Robots
The State Space:

A configuration provides an instantaneous description of the geometry of a
manipulator, but says nothing about its dynamic response.

In contrast, the state of the manipulator is a set of variables that, together
with a description of the manipulator’s dynamics and input, are sufficient to
determine any future state of the manipulator.
“The state space is the set of all possible states.”

A state of the manipulator can be specified by giving the values for the joint
variables
and for joint velocities ̇ (acceleration is related to the derivative of
the joint velocities).

We typically represent the state as a vector:
= ( , ̇)

The dimension of the state space is thus
if the system has
DOF.
Mathematical Modelling of Robots
The Workspace:

The workspace of a manipulator is the total volume swept out by the end-effector as the
manipulator executes all possible motions.

The workspace is constrained by the geometry of the manipulator as well as mechanical
constraints on the joints.

For example, a revolute joint may be limited to less than a full

The workspace is often broken down into a reachable workspace and a dexterous
workspace.

The reachable workspace is the entire set of points reachable by the manipulator, whereas
the dexterous workspace consists of those points that the manipulator can reach with an
arbitrary orientation of the end-effector.

Just think about the furthest points you can touch with your fingertips, that's the outer
boundary of your reachable workspace. The dexterous workspace is made up of all the
points where you could grab a stationary object and still move all your joints as you usually
could.

Obviously the dexterous workspace is a subset of the reachable workspace.
° of motion.
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Robots As Mechanical Devices

There are a number of physical aspects of robotic manipulators that we will not
necessarily consider when developing ur mathematical model.

These include mechanical aspects (e.g., how are the joints actually
implemented), accuracy and repeatability, and the tooling attached at the end
effector.
 Classification of Robotic Manipulators
 Robotic Systems
 Accuracy and Repeatability
 Wrists and End-Effectors
Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Robot manipulators can be classified by several criteria, such as:
 their power source, or way in which the joints are actuated,
 their geometry, or kinematic structure
 their intended application area,
 or their method of control.
 Such classification is useful primarily in order to determine which robot
is right for a given task.
 For example, a hydraulic robot would not be suitable for food handling
or clean room applications.
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Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Power Source:
Typically, robots are either electrically, hydraulically, or pneumatically
powered.
 Hydraulic Based Robot:
 Hydraulic actuators are unparalleled in their speed of response and torque
producing capability.
 Therefore hydraulic robots are used primarily for lifting heavy loads.
 The drawbacks of hydraulic robots are that they tend to leak hydraulic fluid,
require much more peripheral equipment, and they are noisy.
 DC or AC-Servo Based Robot:
 DC or AC servo motors are popular since they are cheaper, cleaner and quieter.

Pneumatic Based Robot:
 Pneumatic robots are inexpensive and simple but cannot be controlled precisely.
 As a result, pneumatic robots are limited in their range of applications and
popularity.
Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Application Area:
Robots are often classified by application into assembly and non-assembly
robots.
 Assembly Robot:
 Assembly robots tend to be small, electrically driven and either revolute or
SCARA in design.
 DC or AC-Servo Based Robot:
 The main non-assembly application areas to date have been in welding, spray
painting, material handling, and machine loading and unloading.
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Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Method of Control:
Method of
Control
Servo
Robots
Non-Servo
Robot
Open loop
Useful primarily for
Movement is
limited to
predetermined
mechanical stops
Servo Robots used
close-loop computer
control to determine
their position.
material transfer
According to
previously given
definition fixed
stop robots hardly
qualify as robots
Multifunctional
and
reprogrammable
Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Method of Control:
Method of
Control
Non-Servo
Robots
Servo
Robots
Point to point robot
Classified according to the
method that the controller uses
to guide the end-effector
Continuous Path
Robot
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Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Method of Control:
Point to Point Robot
Method of
Control
•
A point-to-point robot can be • In continuous path robots, the entire
path of the end-effector. For example,
taught a discrete set of points but
the robot end-effector can be taught to
there is no control on the path of
follow a straight line between two
the end-effector in between the
points or even to follow a contour such
taught points.
as welding seam.
•
Such robots are usually taught a • In addition the velocity and/or
acceleration of the end-effector can
series of points with a teach
often be controlled.
pendant and the points are then
stored and play back.
•
Point-to point robots are severely • These are the most advanced robots
and require the most sophisticated
limited in their range of application.
computer controllers and software
development.
Servo
Robots
Non-Servo
Robots
Point to point
robot
Continuous
Path Robot
Continuous Path Robot
Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Geometry:
 Most industrial manipulators at the present time have six or fewer degree-
of-freedom.
 These manipulators are usually classified kinematically on the basis of the
first three joints of the arm, with the wrist being described separately.
 The majority of these manipulators fall into one of five geometric types:
 Articulated (RRR)
 Spherical
(RRP)
 SCARA
(RRP)
 Cylinderical (RPP)
 Cartesian
(PPP)
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Robots As Mechanical Devices
Classification of Robotic Manipulators:
 Geometry:
 The majority of these manipulators fall into one of five geometric types:
 Articulated (RRR)
 Spherical
(RRP)
 SCARA
(RRP)
 Cylinderical (RPP)
 Cartesian
(PPP)
 Each of these five manipulator arms are a serial link robots.
 A sixth distinct class of manipulators consists of the so called parallel
robots.
 In a parallel manipulator the links are arranged in a closed rather than
open kinematic chain.
 Their kinematic and dynamics are more difficult to derive than those of
serial link robots.
Robots As Mechanical Devices
Robotic Systems:
 A robot manipulator should be viewed as more than just a series of
mechanical linkages.
 The mechanical arm is just one component in an overall Robotic System,
as shown in figure 4, which consists of the arm, external power source,
end-of-arm tolling, external and internal sensors, computer interface and
control computer.
Figure 4: Components of a Robotic System
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Robots As Mechanical Devices
Robotic Systems:
 Even the programmed software should be considered as an integral part
of the overall system, since the manner in which the robot is programmed
and controlled can have a major impact on its performance and
subsequent range of applications.
Figure 4: Components of a Robotic System
Robots As Mechanical Devices
Accuracy and Repeatability:
 The accuracy of a manipulator is a measure of how close the
manipulator can come to a given point within its workspace.
 Repeatability is a measure of how close a manipulator can return to
a previously taught points.
 The primary method of sensing positioning errors in most cases is
with position encoders located at the joints, either on the shaft of the
motor that actuates the joint or one of the joint itself.
 There is typically no direct measurement of the end-effector position
and orientation.
 One must rely on the assumed geometry of the manipulator and its
rigidity to infer (i.e., to calculate) the end-effector position from the
measured joint positions.
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Robots As Mechanical Devices
Accuracy and Repeatability:
How the accuracy is affected?
 Accuracy
is affected therefore by computational errors, machining
accuracy in the construction of the manipulator, flexibility effects such as
the bending of the links under gravitational and other loads, gear
backlash, and other static and dynamic effects.
 It is primarily for this reason that robots are designed with extremely high
rigidity.
 Without high rigidity, accuracy can only be removed by some sort of
direct sensing of the end-effector position such as with vision.
Robots As Mechanical Devices
Accuracy and Repeatability:
How the repeatability is affected?
 Once a point is taught to the manipulator, the above effects are taken into
account and the proper encoder values necessary to return to the given
point are stored by the controlling computer.
 Repeatability therefore is affected primarily by the controller resolution.
Controller resolution means the smallest increment of motion that the
controller can sense.
 The resolution is computed as the total distance traveled by the tip divided
by
, where
is the number of bits of encoder accuracy.
 Linear axis, that is, prismatic joints, typically have higher resolution than
revolute joints, since the straight line distance traversed by the tip of a
linear axis between two points is less than the corresponding are length
traced by the tip of a rotational link.
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Robots As Mechanical Devices
Accuracy and Repeatability:
How the repeatability is affected?
 We will see that rotational axes usually result in a large amount of
kinematic and dynamic coupling among the links with a resultant
accumulation of errors and a more difficult control problem.
 Then what the advantages of revolute joints are in a manipulator design.
 Increased dexterity.
 Compactness of revolute joint designs. For example Figure 5 shows that for
the same range of motion, a rotational link can be made much smaller than a
link with linear motion.
 Manipulators made from revolute joints occupy a smaller working volume
than manipulators with linear axes.
 Revolute joint manipulators are better able to maneuver around obstacles
and have a wider range of possible applications.
Figure 5: Linear vs. Rotational link motion
Robots As Mechanical Devices
Wrists and End-Effectors:
 The joints in the kinematic chain between the arm and end-effector are
referred to as the wrist.
 The wrist joints are nearly always all revolute.
 It is increasingly common to design manipulators with spherical wrists,
by which we mean wrists whose three joint axes intersect at a common
point as shown in figure 6.
Figure 6: Structure of a spherical wrist.
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Robots As Mechanical Devices
Wrists and End-Effectors:
 The spherical wrist greatly simplifies the kinematic analysis, effectively
allowing one to decouple the positioning and orientation of the end
effector.
 The arm and wrist assemblies of a robot are used primarily for positioning
the end-effector and any tool it may carry.
 It is the end-effector or tool that actually performs the work. The simplest
type of end-effectors are grippers, which usually are capable of only two
actions, opening and closing.
Common Kinematic Arrangements of Manipulators
There are many possible ways use prismatic and revolute joints to
construct kinematic chains, in practice only a few of these are
commonly used.
Articulated Manipulator (RRR):
 The
articulated manipulator is also called revolute, or
anthropomorphic manipulator. Figure 7 shows two different
articulated arms.
Figure 7: (a) ABB IRB1400 Robot {b} Motoman SK16 manipulator
21
Common Kinematic Arrangements of Manipulators
Articulated Manipulator (RRR):
 In both of these arrangements joint axis
and
are perpendicular to
is parallel to
and both
.
 This kind of manipulator is known as an elbow manipulator. The
structure and terminology associated with the elbow manipulator are
shown in figure 8a and its workspace is shown in figure 8b.
Figure 8: (a) Structure of the elbow manipulator (b) Workspace of the elbow manipulator
Common Kinematic Arrangements of Manipulators
Spherical Manipulator (RRP):
 By replacing the third or elbow joint in the revolute manipulator by a
prismatic joint one obtains the spherical manipulator shown in figure 9(a).
 Figure 9(b) shows the Stanford Arm, one of the most well known spherical
robots.
 The workspace of a spherical manipulator is shown in figure 9(c).
Figure 9: (a) The Spherical manipulator (b) The Stanford Arm (c) Workspace of the spherical manipulator
22
Common Kinematic Arrangements of Manipulators
SCARA Manipulator (RRP):
 The SCARA arm (for Selective Compliant Articulated Robot for Assembly)
shown in figure 10(a).
 Unlike the spherical design, which has
perpendicular to
, the SCARA has
,
perpendicular to
, and
, and
mutually parallel.
 Figure 10(b) shows the Epson, manipulator of this type. Whereas, the
SCARA manipulator workspace is shown in figure 10(c)
Figure 10: (a) The SCARA (b) The Epson Robot (c) Workspace of the SCARA manipulator
Common Kinematic Arrangements of Manipulators
Cylindrical Manipulator (RPP):
 The cylindrical manipulator shown in figure 11(a). The first joint is
revolute and produces a rotation about the base, while the second and
third joints are prismatic.
 Figure 11(b) shows a cylindrical robot Seiko RT3300 with its workspace in
figure 11(c).
Figure 11: (a) The cylinderical manipulator (b) The Seiko RT3300 Robot (c) Workspace of the cylinderical manipulator
23
Common Kinematic Arrangements of Manipulators
Cartesian Manipulator (PPP):
 A manipulator whose first three joints are prismatic is knows as a Cartesian
manipulator, shown in figure 12(a).
 For the Cartesian manipulator the joint variables are the Cartesian coordinates
of the end-effector with respect to the base.
 The kinematic description of this manipulator is the simplest of all manipulators
and useful for table-top assembly applications, for transfer of material or cargo.
 Example of Cartesian Epson robot shown in figure 12(b), whereas the
workspace shown in figure 12(c).
Figure 12: (a) The Cartesian manipulator (b) The Epson Robot (c) Workspace of the Cartesian manipulator
Common Kinematic Arrangements of Manipulators
Parallel Manipulator:
 A parallel manipulator is one in which some subset of the links form a closed
chain.
 A
parallel manipulator has two or more independent kinematic chains
connecting the base to the end-effector.
 Figure 13 shows ABB Tricep robot, which is a parallel manipulator.
 The closed chain kinematics of parallel robots can result in greater structural
rigidity, and hence greater accuracy, than open chain robots.
 The kinematic description of parallel robots is fundamentally different from that
of serial link robots and therefore required methods of analysis.
Figure 13: The ABB Tricep Parallel Robot
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