Robotics

EC368 Robotics
Dr. A. R. Jayan, ECE Dept.,

GEC Sreekrishnapuram
1 Feb. 2019
Dr. A. R. Jayan, ECE Dept., GEC Sreekrishnapuram EC368 Robotics 1 Feb. 2019 1 / 71
Robotics
Module 1 Introduction – Definition and origin of robotics, Robot

Anatomy, Robot specifications, Robot characteristics – accuracy,
precision, and repeatability, Areas of application, classification of
robots. Robotic arm – Components and structure, Types of joints and
workspace, Common kinematic arrangements, Wrists, End effectors.
Robot
A robot is a software controllable mechanical device that uses sensors

to guide one or more end-effectors through programmed motion in a
workspace in order to manipulate physical objects.
Robot generations
First generation: designed to do simple tasks: Welding, spray

painting
Secong generation: designed to do complex tasks, simulate
human functions, sense surroundings, respond to changes in the
environment
Sophia
World’s first robot citizen!
Automation
Mass production assembly lines (1905, Ford motor company)

Hard automation: Specialised machines designed and developed
for high volume production of mechanical and electrical parts.
Drawback: When new model parts are to be introduced,
retooling is needed → Limited flexibility.
Soft automation: Computer controlled programmable
mechanical manipulators (Robots)
Hard and soft automation
Hard automation: high initial investment, unit cost reduces for

large production volume
Soft Automation: Moderate initial investment. Works well for
production volume in a certain range
Manual labour: item cost not much affected by variation in
production volume
Cost-Effectiveness
Low production volumes (< V1 ): manual labour

Soft automation: for production volumes V1 < V ≤ V2
Hard automation: for production volumes V > V2
So Robots are cost effective for production volumes [V1 , V2 ]
Unit cost, Production volume
Anatomy of robots
Deals with physical construction of body, arm, wrist.

The combination of body, arm, and wrist is called manipulator
Tool attached to the wrist is called end effector
Body is attached to the base, arm is attached to the body, wrist
is attached to the arm, end effector is attached to the wrist
Robot anatomy
Robot: Joints
A loose object moves when a force is applied to it.

Robots need controlled motion.
A set of connected pieces moving in a constrained but useful
pattern is needed in robotics.
A point where two rigid parts are attached and where they move
relative to each other is called a moving joint.
A joint may allow bending motion, sliding, rotation.
Type of Robot Joints
Revolute joints (R): Exhibit rotary motion about an axis (most

common)
Prismatic joint (P): Exhibit sliding or linear motion about an axis
The combination of revolute and prismatic joints for the three major
axes determines the geometry of the work envelope.
Equivalence between humans and robots
Arms and fingers: manipulation of objects

Legs: locomotion
Muscles: Actuators
Eyes: Vision
Nose: Smelling
Ear: hearing
Tongue: taste
Skin: Temperature, touch
Brain connected with nerves: Thoughts → Communication →
actuation
Robotics: Observe nature → Understand nature → Mimic nature
Components of a Robot
Actuators: Solenoids, motors

Mechanisms: arrangements to convert rotary or linear motion to
some useful form or pattern
Power supplies
Sensors
Micro controller
Algorithm
Actuators
The term used for a mechanism that drives a Robot arm is actuator.
These actuators may be electric motors of some type or hydraulic or
pneumatic cylinders.
Hydraulic and pneumatic actuators are generally suited to driving
prismatic joints since they produce linear motion directly. They are
often referred to as linear actuators.
Electric motors which produce rotation are more suited to driving
revolute joints.
However various gear mechanisms may be used to convert linear to
rotary motion and vice versa.
Robot Classification
Classification based on the source of power used to drive the joints of

the robot.
Electric
Hydraulic
Pneumatic
Electric Drives
DC Stepper motors: one pulse = 1.8 degress

DC Servo motors: feedback to sense motor shaft position
Hydraulic drives
The underlying principle of all hydraulic systems is Pascal’s Law,

which states:- If external pressure is applied to a confined fluid, the
pressure is transferred without loss to all surfaces in contact with the
fluid.
For high speed manipulation of substantial loads.
Drawbacks:
Cylinder filled with compressible fluids
Ensure no air bubbles: For precise control
Can be stopped in between positions
Lack of cleanliness
Example: Automobile power braking systems, power steering
systems..
Pneumatic drives
Mechanical work put in is used to compress the air. The system for
pumping air into a pneumatic cylinder is much simpler than the
hydraulic system. This is mainly because there is no point
recirculating the air. Used air expelled from the cylinder is released to
the atmosphere via a valve.
Drawbacks:
Compressible, position may depend on load.
Cannot be stopped in between (We may put external rings for
stopping)
Comparison of robot drive systems
Pneumatic systems are generally less expensive than hydraulic

systems. Small leakage’s can be tolerated.
The compressibility of air can be a safety feature e.g. bus and train
doors are pneumatic and will not crush you if you get trapped. This
can be of use in the gripper of the robot to protect both the robot
and the equipment etc. with which it is working.
Pneumatic drives are faster to respond than hydraulic drives.
Work Envelope
Locus of points in three dimensional space that can be reached by

the Robot’s wrist.
Major axes: First three joints of a robot → defines the position of
the wrist.
Minor axes: Axes of remaining joints → used to establish orientation
of the tool.
Degree of Freedom
Robot arms are described by their degrees of freedom.

The degrees of freedom (DOF) of a rigid body is defined as the
number of independent movements it has.
In physics, the degree of freedom (DOF) of a mechanical system is
the number of independent parameters that define its configuration.
... The position and orientation of a rigid body in space is defined by
three components of translation and three components of rotation,
which means that it has six degrees of freedom.
A higher number indicates an increased flexibility in positioning a
tool.
Degree of Freedom
3 dimensional plane - 6 degrees of freedom
2D plane
In a two dimensional plane such as this computer screen, there are 3

DOF. The bar can be translated along the x axis, translated along
the y axis, and rotated about its centroid.
2D plane, 3 DOF
Six Degrees of Freedom
Six degrees of freedom (6 DoF) refers to the freedom of movement of

a rigid body in three-dimensional space. Specifically, the body is free
to move forward/backward, up/down, left/right (translation in three
perpendicular axes) combined with rotation about three perpendicular
axes, often termed pitch, yaw, and roll.
3D plane, 6 DOF
Revolute pair
Prismatic pair
Some possible robot coordinate frames
Cartesian (3P)
Cylindrical (PRP)
Cylindrical
Spherical (PRR or P2R)
Spherical
Articulated (3R)
Articulated
Similar to human arm
SCARA
SCARA: Selective Compliance Assembly Robot Arm.

SCARA robots have two or three R joints that are all parallel and
allow robot to move in a horizontal plane plus an additional prismatic
joint that move vertically. SCARA robots are very complaint in the
X-Y plane and very stiff in the Z plane.
System
Definition: A complex whole set of connected things or parts

organised body of material or immaterial things.
Dynamic system: Three elements: Input, state, output.
+ A rule of transition from the current state to the future state.
State: a function of input and previous state.
The state of a dynamic system is determined not only by the
value of the input, but also by the history of that input.
Dynamic systems are said to have memory.
Systems
Static Systems: State is dependent only on the input at the current

time → no memory.
Causal systems: systems with input and history of input influence
the state of the system. Future inputs cannot influence it.
Non causal systems: systems whose state is a result of future
values of the input → anticipatory or non causal.
Intelligent Robots
Intelligent machine/robot is expected to

Perceive the environment
Reason about the perceived information
Make decisions based on this perception
Act according to a higher level plan
Bring me a glass of water without spilling it
Robot as a mechanical system
A robotic system is composed of the following subsystems

A mechanical subsystem composed of rigid / deformable bodies
A sensing subsystem
An actuation subsystem
A controller
An information processing subsystem
Systems
Systems
General structure of a robotic mechanical system
Manipulation
Manipulation: move something with one’s hands.

manus means hand
Hands are among the organs that human brain can control with the
highest accuracy.
Manipulators
A combination of links and joints.

There are two types of manipulators
Serial chains
Parallel chains
R and P joints
Revolute joint: by motor

Prismatic joint: by cylinder and piston
Robot Characteristics
Payload
Reach
Precision
Repeatability
Payload
Payload is the weight a robot can carry and still remain within its
other specifications.
Normally a robot’s maximum load capacity is much higher than the
specified payload. At these levels, robot may become less accurate
and may not accurately follow its intended trajectory.
Reach
Maximum distance a robot can reach within its work envelope. Reach
is a function of robot’s joints and lengths and its configuration.
Precision (validity)
Precision is the accuracy with which a specified point can be

reached. This is a function of the resolution of the actuators as well
as the robot’s feedback devices.
Industrial robots: Precision 0.001 inches or better.
Repeatability (variability)
The accuracy with which the same position can be reached if the
motion is repeated many times.
Repeat the same motion a number of times.
Robot may not reach the same point every time, but will be
within a certain radius every time from the desired point.
Radius of the circle formed by the repeated motions is called
repeatability
Repeatabiltiy is much more important than precision.
Precision: can be predicted and corrected through software.
Repeatability: measures randomness - cannot be easily corrected.
Repeatabilty
Roughly speaking, the repeatability of a robot might be defined as its

ability to achieve repetition of the same task.
Accuracy is the difference (i.e. the error) between the requested task
and the obtained task (i.e. the task actually achieved by the robot).
Repeatability is doing the same task over and over again, while
accuracy is hitting your target each time.
Repeatabilty
Repeatabilty
Assignment 1: Robot Applications
Briefly explain the application areas of Robots.

Deadline: 29/1/2018
Robot joints
The manipulator of an industrial robot consists of a series of

joints and links.
Robot anatomy deals with the study of different joints and links
and other aspects of the manipulator’s physical construction.
A robotic joint provides relative motion between two links of the
robot.
Each joint, or axis, provides a certain degree-of-freedom (dof) of
motion. In most of the cases, only one degree-of-freedom is
associated with each joint.
Robot joints
Each joint is connected to two links, an input link and an output

link.
Joint provides controlled relative movement between the input
link and output link.
A robotic link is the rigid component of the robot manipulator.
Most of the robots are mounted upon a stationary base, such as
the floor.
Links are normally numbered starting from the base.
Robot joints
Type of Robot joints
Robot joints
Linear joint (type L joint): The relative movement between the

input link and the output link is a translational sliding motion,
with the axes of the two links being parallel.
Orthogonal joint (type U joint): Translational sliding motion,
but the input and output links are perpendicular to each other.
Rotational joint (type R joint): Rotational relative motion, with
the axis of rotation perpendicular to the axes of the input and
output links.
Twisting joint (type T joint): Rotary motion, but the axis or
rotation is parallel to the axes of the two links.
Revolving joint (type V-joint): Axis of input link is parallel to
the axis of rotation of the joint. However the axis of the output
link is perpendicular to the axis of rotation.
Robot configurations
Basically the robot manipulator has two parts: a body-and-arm

assembly with three degrees-of-freedom; and a wrist assembly with
two or three degrees-of-freedom. For body-and-arm configurations,
different combinations of joint types are possible for a
three-degree-of-freedom robot manipulator.
Common Robot configurations
a. Polar configuration: a sliding joint, which rotates around both a

vertical axis (T-joint), and horizontal axis (R-joint).
b. Cylindrical configuration: It consists of a vertical column. An arm
assembly is moved up or down relative to the vertical column. The
arm can be moved in and out relative to the axis of the column.
c. Cartesian co-ordinate robot: It is also known as rectilinear robot
and x-y-z robot. It consists of three sliding joints, two of which are
orthogonal O-joints.
d. Jointed-arm robot: It is similar to the configuration of a human
arm. It consists of a vertical column that swivels about the base
using a T-joint. Shoulder joint (R-joint) is located at the top of the
column. The output link is an elbow joint (another R joint).
SCARA
Selective Compliance Assembly Robot Arm: It is similar in

construction to the jointer-arm robot, except the shoulder and elbow
rotational axes are vertical. It means that the arm is very rigid in the
vertical direction, but compliant in the horizontal direction.
Robot Wrist
Robot wrist assemblies consist of either two or three

degrees-of-freedom. The roll joint is accomplished by use of a T-joint.
The pitch joint is achieved by recourse to an R-joint. And the yaw
joint, a right-and-left motion, is gained by deploying a second R-joint.
Drive Systems
Electric
Hydraulic
Pneumatic
Pneumatic drives
Pneumatic drive is regularly used for smaller, simpler robotic

applications; whereas electric and hydraulic drives may be found
applications on more sophisticated industrial robots.
Electric drives
Due to the advancement in electric motor technology made in recent

years, electric drives are generally favored in commercial applications.
They also have compatibility to computing systems.
Hydraulic drives
Hydraulic systems, although not as flexible as electrical drives, are

generally used where larger speeds are required. They are generally
employed to carry out heavy duty operations using robots.
Load carrying capacity
Load carrying capacity is also an important factor. It is determined by

weight of the gripper used to grasp the objects. A heavy gripper puts
a higher load upon the robotic manipulator in addition to the object
mass. Commercial robots can carry loads of up to 900 kg, while
medium-sized industrial robots may have capacities of up to 45kg.

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EC368 Robotics

Dr. A. R. Jayan, ECE Dept.,

Module 1 Introduction – Definition and origin of robotics, Robot

A robot is a software controllable mechanical device that uses sensors

First generation: designed to do simple tasks: Welding, spray

World’s first robot citizen!

Mass production assembly lines (1905, Ford motor company)

Hard automation: high initial investment, unit cost reduces for

Low production volumes (< V1 ): manual labour

Deals with physical construction of body, arm, wrist.

A loose object moves when a force is applied to it.

Revolute joints (R): Exhibit rotary motion about an axis (most

Arms and fingers: manipulation of objects

Actuators: Solenoids, motors

Classification based on the source of power used to drive the joints of

DC Stepper motors: one pulse = 1.8 degress

The underlying principle of all hydraulic systems is Pascal’s Law,

Pneumatic systems are generally less expensive than hydraulic

Locus of points in three dimensional space that can be reached by

Robot arms are described by their degrees of freedom.

3 dimensional plane - 6 degrees of freedom

In a two dimensional plane such as this computer screen, there are 3

Six degrees of freedom (6 DoF) refers to the freedom of movement of

Similar to human arm

SCARA: Selective Compliance Assembly Robot Arm.

Definition: A complex whole set of connected things or parts

Static Systems: State is dependent only on the input at the current

Intelligent machine/robot is expected to

A robotic system is composed of the following subsystems

Manipulation: move something with one’s hands.

A combination of links and joints.

Revolute joint: by motor

Precision is the accuracy with which a specified point can be

Roughly speaking, the repeatability of a robot might be defined as its

Briefly explain the application areas of Robots.

The manipulator of an industrial robot consists of a series of

Each joint is connected to two links, an input link and an output

Linear joint (type L joint): The relative movement between the

Basically the robot manipulator has two parts: a body-and-arm

a. Polar configuration: a sliding joint, which rotates around both a

Selective Compliance Assembly Robot Arm: It is similar in

Robot wrist assemblies consist of either two or three

Pneumatic drive is regularly used for smaller, simpler robotic

Due to the advancement in electric motor technology made in recent

Hydraulic systems, although not as flexible as electrical drives, are

Load carrying capacity is also an important factor. It is determined by

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