Chapter 1

1 | D e b r e M a r k o s u n i v e r s i t y C o m p i l e d b y A s a l i f e w B .
Chapter 1
Background
1. Introduction
Many definitions have been suggested for what we call a robot. The word may conjure up
various levels of technological sophistication, ranging from a simple material handling device to
a humanoid. The image of robots varies widely with researchers, engineers, and robot
manufacturers. However, it is widely accepted that today’s robots used in industries originated in
the invention of a programmed material handling device by George C. Devol. In 1954, Devol
filed a U.S. patent for a new machine for part transfer, and he claimed the basic concept of teach-
in/playback to control the device. This scheme is now extensively used in most of today's
industrial robots.
Word robot was coined by a Czech novelist Karel Capek in a 1920 play titled Rassum’s
Universal Robots (RUR. Robot in Czech is a word for worker or servant.
Definition of robot:
–A robot is a reprogrammable, multifunctional manipulator designed to move material, parts,
tools or specialized devices through variable programmed motions for the performance of a
variety of tasks: Robot Institute of America, 1979
1.1 History of Robotics
• 1954: The first programmable robot is designed by George Devol, who coins the term
Universal Automation. He later shortens this to Unimation, which becomes the name of the first
robot company (1962).
1978: The Puma (Programmable Universal Machine for Assembly) robot is developed by
Unimation with a General Motors design support

Fig. 1.1 PUMA 560 Manipulator
1980s: The robot industry enters a phase of rapid growth. Many institutions introduce programs
and courses in robotics. Robotics courses are spread across mechanical engineering, electrical
Engineering and computer science departments.
Fig. 1.2 Robots
1995-present: Emerging applications in small robotics and mobile robots drive a second growth
of start-up companies and research.

Fig. 1.3 mobile robot
1.2 Knowledgebase for Robotics
Typical knowledgebase for the design and operation of robotics systems
 Dynamic system modeling and analysis
 Feedback control
 Sensors and signal conditioning
 Actuators (muscles) and power electronics
 Hardware/computer interfacing
 Computer programming
Fig 1.4 key component of robot

RobotBase:Fixed v/s Mobile
Robotic manipulators used in manufacturing are examples of fixed robots. They cannot move
their base away from the work being done. Mobile bases are typically platforms with wheels or
tracks attached. Instead of wheels or tracks, some robots employ legs in order to move about.
(a) (b)
Fig. 1.5 (a) fixed robot (b) mobile robot
Robots in Industry
 Agriculture
 Automobile
 Construction
 Entertainment
 Health care: hospitals, patient-care, surgery, research, etc.
 Laboratories: science, engineering, etc.
 Law enforcement: surveillance, patrol, etc.
 Manufacturing
 Military: demining, surveillance, attack, etc.Mining, excavation, and exploration
 Transportation: air, ground, rail, space, etc.
 Utilities: gas, water, and electric
 Warehouses

Industrial Applications of Robots
 Material handling
 Material transfer
 Machine loading and/or unloading
 Spot welding
 Continuous arc welding
 Spray coating
 Assembly
 Inspection
Robot Terminology
Exactly what constitutes a robot is sometimes debated. Numerically controlled (milling)
machines are usually not referred as robots. The distinction lies somewhere in the sophistication
of the programmability of the device – if a mechanical device can be programmed to perform a
wide variety of applications; it is probably an industrial robot. Machines which are for the most
part relegated to one class of task are considered fixed automation.
Industrial robots consist of (nearly) rigid links which are connected with joints which allow
relative motion of neighboring links. These joints are usually instrumented with position sensors
which allow the relative position of neighboring links to be measured. In case of rotary or
revolute joints, these displacements are called joint angles. Some robots contain sliding, or
prismatic joints.
The number of degrees of freedom that a robot possesses is the number of independent position
variables which would have to be specified in order to locate all parts of the mechanism.
At the free end of the chain of links which make up the robot is the end effector. Depending on
the intended application of the robot, the end effector may be a gripper, welding torch or any
other device. We generally describe the position of the manipulator by giving a description of the
tool frame or sometimes called the TCP frame (TCP=Tool Center Point), which is attached to
the end-effector, relative to the base frame which is attached to the nonmoving base of the
manipulator.

Frames (coordinate systems) are used to describe the position and orientation of a rigid body in
space. They serve as a reference system within which to express the position and orientation of a
body.
Manipulators
Manipulators are composed of an assembly of links and joints. Links are defined as the rigid
sections that make up the mechanism and joints are defined as the connection between two links.
The device attached to the manipulator which interacts with its environment to perform tasks is
called the end-effector. In Fig.1.5, link 6 is the end effector.
Fig. 1.5: Links and joints
Types of Joints
Joints allow restricted relative motion between two links. The following table describes
five types of joints.

Some ClassificationofManipulators
Manipulators can be classified according to a variety of criteria. The following are two of
these criteria:
By Motion Characteristics
Planar manipulator: A manipulator is called a planar manipulator if all the moving links move
in planes parallel to one another.
Spherical manipulator: A manipulator is called a spherical manipulator if all the links perform
spherical motions about a common stationary point.
Spatial manipulator: A manipulator is called a spatial manipulator if at least one of the links of
the mechanism possesses a general spatial motion.
By Kinematic Structure
Open-loop manipulator (or serial robot): A manipulator is called an open-loop manipulator if
its links form an open-loop chain.
Parallel manipulator: A manipulator is called a parallel manipulator if it is made up of a
closed-loop chain.

Hybrid manipulator: A manipulator is called a hybrid manipulator if it consists of open loop
and closed loop chains.
Degrees of Freedom
The number of degrees of freedom that a robot possesses is the number of independent position
variables which would have to be specified in order to locate all parts of the mechanism in space.
Usually a robot is an open kinematic chain. This implies that each joint variable is usually
defined with a single variable and the number of joints equals the number of degrees of freedom.
The number of degrees of freedom for a manipulator can be calculated as
……………………………..(eq.1)
Where n is the number of links (this includes the ground link), J is the number of joints, fi is the
number of degrees of freedom of the ith joint and λ is 3 for planar mechanisms and 6 for spatial
mechanisms.
Eq.1 can also be expressed as
……………………………………………(eq.2)
Fig. Revolute Joint 1 DOF (Variable -)

Fig. Prismatic Joint 1 DOF (linear) (Variables - d)
Fig. Spherical Joint 3 DOF (Variables - 1, 2, 3)
1.3 Robotkinematics;rigid body motion transformation of coordinates
Kinematics is the science of motion which treats motion without regard to the forces which
cause it. Within the science of kinematics one studies the position, velocity, acceleration, and all
higher order derivatives of the position variables. Hence, the study of the kinematics of robots
refers to all geometrical and time-based properties of the motion.
Description of a Position
The most used and familiar coordinate system is the Cartesian coordinate system. Most will be
familiar with this as the X, Y; axis is at 90° to each other. A point can be located on a plane by
locating the distance of a point from its origin (0, 0) along each axis. This is a 2 dimensional
representation, hence the two axis X & Y.

To find a point in space it is necessary to add a third axis (Z).This third axis will form a 3
dimensional grid that matches a set of coordinates to a single point in space.
The axes of machines are always defined by what is known as the right-hand rule. If we take the
thumb as pointing in the direction of the positive X-Axis then the second finger is pointing
towards the positive Y-Axis and the middle finger towards the positive Z-Axis. The Z axis is
always in the direction of the spindle or grab arm as shown in the ‘Cartesian Robot’ below.

Fig. Right hand rule
Cartesian Robots:
Cartesian robots are used for pick and place work, application of sealant, assembly operations,
handling machine tools and arc welding. It’s a robot whose arm has three prismatic joints, whose
axes are coincidental with the Cartesian coordinators.
The position of any point in space, relative to a reference frame, can be described by a 3x1
position vector. For example, the position of point P (see Fig. 1.6) with respect to frame A can be
written as
……………………… (eq.2)
Where px, py, and pz are the magnitudes of the projections of the line joining the point p and the
origin o on the x,y and z axes respectively.

Fig. 1.6: Position vector
Description of an Orientation
The orientation of a body in space can be described by attaching a coordinate system to it and
then describing the vectors of its coordinate axes relative to a known frame of reference. For
example, the coordinate axes of Frame B (see Fig. 1.7) can be described relative to a known
coordinate system A by the following unit vectors:
………………………….. (eq.3)
These three vectors can be combined to achieve a 3x3 matrix called a rotation matrix.
………………………. (eq.4)

Fig. 1.7: Components of the rotation matrix of Frame B w.r.t Frame A
Principal Rotation Matrices
Rotation about the z-axis
If a reference frame (Frame A) is rotated by an angle about the z-axis to obtain a new frame
(Frame B), the rotation matrix of the new frame is
……………………………….(eq.5)

Fig. 1.8: Rotation about the z-axis
Rotation about the y-axis
If a reference frame (Frame A) is rotated by an angle about the y-axis to obtain a new frame
……………………………..(eq.6)

Fig.1.8: Rotation about the y-axis
Rotation about the x-axis
If a reference frame (Frame A) is rotated by an angle about the x-axis to obtain a new frame
……………………………….(eq.7)

Fig.1.8: Rotation about the-x axis
Finding the Homogeneous Matrix
Example

H = (Translation relative to the XYZ frame) * (Rotation relative to the XYZ frame) *
(Translation relative to the IJK frame) * (Rotation relative to the IJK frame)
One more variation on finding H:
H = (Rotate so that the X-axis is aligned with T)
* (Translate along the new t-axis by || T || (magnitude of T))
* (Rotate so that the t-axis is aligned with P)
* (Translate along the p-axis by || P || )
* (Rotate so that the p-axis is aligned with the O-axis)
This method might seem a bit confusing, but it’s actually an easier way to solve our problem
given the information we have.

Chapter 1

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