Lecture 1.pdf

Industrial Robotics
Dr Beteley Teka
Asst Prof, Department of Electronics Engineering
ECEg 7245

Contents
Fundamentals of Robot Technology
Industrial Applications and Robot Programming
Transformation , Rigid Motion and Kinematics:
Robot arm dynamics
Path and Trajectory Generation/planning
Robot Control
Machine Vision System
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Beteley Teka, Asst. Prof, Electronics
Engineering dept, DEC

Robots
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Word robot was coined by a Czech novelist Karel Capek in
a 1920 play titled Rassum‟s Universal Robots .
Robota/Robot in Czech is a word for worker/servant.
The term 'robotics' was coined by Isaac Asimov in about
1940
Robotics is a subject without sharp boundaries: at various
points on its periphery it merges into fields such as
artificial intelligence, automation and remote control, so it
is hard to define it concisely
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Random House Dictionary:
A machine that resembles a human being and does mechanical
routine tasks on command.
Robotics Association of America
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:
Definition of robot:
Oxford dictionary:
A machine resembling a human being and able to
replicate certain human movements and functions
automatically.
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Industrial robots?
Currently robots are a combination of manipulative,
perceptive, communicative, and cognitive abilities.
Today's robots are capable of so many tasks. Yet, there is
so much more on the horizon.
A manipulator (or an industrial robot) is composed
of a series of links connected to each other via
joints. Each joint usually has an actuator (eg. motor)
connected to it
These actuators are used to cause relative motion between
successive links. One end of the manipulator is usually connected to a
stable base and the other end is used to deploy a tool.
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The term manipulator is used here to mean any device
with an arm bearing a hand or gripper; thus it includes
both industrial robots and telemanipulators.
An industrial robot is a manipulator which automatically
repeats a cycle of operations under program control.
Industrial robots?
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As the field of robotics rapidly progresses it is not
necessarily a bad thing that everyone has not agreed on a
universal definition for a robot:
Joseph Engelberger (father of the industrial
robot) :
"I may not be able to define one, but I know one when I
see one."
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Robot capabilities:
Sensing and perception: get information from its
surroundings.
Carry out different tasks: Locomotion or
manipulation, do something physical–such as move or
manipulate objects.
Re-programmable: can do different things in
different ways.
Function autonomously and/or interact with human
beings.
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Laws of Robotics
Isaac Asimov proposed the following three Laws of
Robotics:
Law 1: A robot may not injure a human being or through inaction,
allow a human being to come to harm.
Law 2: A robot must obey orders given to it by human beings,
except where such orders would conflict with a higher order law.
Law 3: A robot must protect its own existence as long as such
protection does not conflict with a higher order law.
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Classification of Robots
JIRA (Japanese Industrial Robot Association):
Class1: Manual-Handling Device
Class2: Fixed Sequence Robot
Class3: Variable Sequence Robot
Class4: Playback Robot
Class5: Numerical Control Robot
Class6: Intelligent Robot
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Classification of Robots
RIA (Robotics Institute of America):
Variable Sequence Robot (Class3): A device that performs
the successive stages of a task according to a
predetermined method easy to modify.
Playback Robot (Class4): A human operator performs the
task manually by leading the Robot.
Numerical Control Robot (Class5): The operator
supplies the movement program rather than teaching it
the task manually.
Intelligent Robot (Class6): A robot with the means to
understand its environment and the ability to
successfully complete a task despite changes to the
environment.
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History of Robotics
1922: Karel Čapek‟s novel, Rossum‟s Universal Robots, word
“Robota” (worker).
1952: NC machine (MIT)
1954 George Devol developed the first programmable
Robot.
1955: Denavit-Hartenberg Homogeneous Transformation.
First Commercial Robot (1962)
1967: Mark II (Unimation Inc.)
1968: Shakey (SRI) - intelligent robot.
1973: T3 (Cincinnati Milacron Inc.)
1978: PUMA (Unimation Inc.)
1983: Robotics Courses
21C: Walking Robots, Mobile Robots, Humanoid Robots
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Advantages
Robots increase productivity, safety,
efficiency, quality, and consistency of
products.
Robots can work in hazardous
environments without the need.
Robots need no environmental
comfort.
Robots work continuously without
experiencing fatigue of problem.
Robots have repeatable precision at
all times
Robots can be much more accurate
than human.
Robots can process multiple stimuli or
tasks simultaneously
Disadvantages
Robots lack capability to
respond in emergencies
Robots, although superior in
certain senses, have limited
capabilities in Degree of
freedom, Dexterity,
Sensors, Vision system, real
time response
Robots are costly, due to
Initial cost of equipment,
Installation costs, Need for
Peripherals, Need for
training, Need for
programming
Robots replace human
workers creating economic
problems.
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Types of Robots
Manipulator
Mobile robots: wheeled/legged
Autonomous Underwater Vehicle
/Unmanned Aerial Vehicle .
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Manipulators: Type I
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Wheeled and legged : Type II
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Type III
Underwater and Aerial and legged
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Where to use?
Application in 4D environments
Dangerous
Dirty
Dull
Difficult
4A tasks
Automation
Augmentation
Assistance
Autonomous
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Why to use?
Increase product quality:
Superior Accuracies (thousands of an inch, wafer handling: microinch)
Repeatable precision
Consistency of products
Increase efficiency:
Work continuously without fatigue
Need no vacation
Operate in dangerous environment
Need no environmental comfort:
Air conditioning, noise protection, etc.
Reduce Cost:
Reduce scrap rate
Lower in-process inventory
Lower labor cost
Reduce manufacturing
lead time:
 Rapid response to
changes in design
Increase productivity:
 Value of output per
person per hour increases
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Classification
Robots can be classified according to:
Use
Mobility
Motion control
Capability
Arm configuration
End effector
Robot classification: according to
1) Co-ordinate system: Cartesian, cylindrical,
spherical, SCARA, Articulated
2) Control Method: Servo controlled and non-
servo controlled, their comparative study
,
3) Form of motion: P-T-P (point to point), C-P
(continuous path), pick and place etc. and
their comparative study,
4) Drive Technology: Hydraulic, Pneumatic,
Electric (stepper motor, D.C. servo motor) in
detail with selection criteria. Motion
conversion: Rotary to rotary, rotary to linear
and vice versa
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Integral Parts of a Robot
Robot Anatomy
Drive System
Control System
Sensors
Actuators / End
Effectors
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Integral Parts of a Robot(industrial)
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Robot Structure(serial)
Joint :
Relative motion between two parts of the
robot body.
Joint provides the robot with degree-of-
freedom of motion (DOF).
The individual joint motions associated with the
performance of a task are referred to by the term
Degrees of freedom DOF
In most cases, 1 DOF is associated with a
joint.
Robots are often classified according to
total number of DOF they posses.
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Links: are rigid components of the robot
manipulator
Robot structure(serial)
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Basic robot structure: Joints & Links
Linear joint, L
Orthogonal Joint, O
Rotational Joint, R
Twisting Joint, T
Revolving Joint, V
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Basic Joints
Spherical Joint
3 DOF ( Variables - X, , Z)
Revolute Joint
1 DOF ( Variable - )
Prismatic Joint
1 DOF (linear) (Variables -
X)
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This robot arm has SIX revolute joints:
A revolute joint has ONE degree of freedom ( 1 DOF) that is
defined by its angle
1
2
3
4
There are two more
joints on the end
effector (the
gripper)
Example: PUMA Robot
Programmable Universal Manipulation Arm
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PUMA Robot
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• Developed in 1981
• Used mainly for assembly operations
SCARA
Example: SCARA Robot
Selective Compliant Assembly Robot Arm
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3 DOF wrist assembly
Wrist Roll: also known as wrist
swivel, this involves rotation of the
wrist mechanism about the arm axis.
Wrist Pitch: Given that the wrist
roll is in its center position, the
pitch would involve the up or down
rotation of the wrist. It is also
known as wrist bend.
Wrist Yaw: Given that the wrist roll
is in its center position of its range,
wrist yaw would involve the right or
left rotation of the wrist
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Basic Robot Configurations
Cylindrical: approximates
a Cylinder Cartesian
Jointed-Arm
Polar: Spherical
coordinate
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DOF associated with arm and body
motions
For robots of polar, cylindrical or
jointed-arm configuration, the
3DOF are:
Vertical transverse: capability to move
the wrist up or down to provide the
desired vertical attitude.
Radial transverse: This involves the
extension or retraction (in and out
movement) of the arm from the vertical
center of the robot.
Rotational transverse: this is rotation
of the arm about the vertical axis
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Work volume (workspace)
The industrial robots are designed to perform some desirable work
This can be performed by enabling the manipulator to move the body,
arm and wrist through a series of motions
It helps the end effectors of the robot to achieve the desirable
position and orientation in the three dimensional space surrounding
the base of the robot .
A robot joint 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 .
The end effector is mounted on a flange or some plate secured to the
wrist.
It is the tool to perform some operation or some gripper for pick and
place operations
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The workspace represents that portion of the environment the
manipulator‟s workspace can access.
Its shape and volume depend on the manipulator structure as well as the
presence of mechanical joint limits.
The task required of the arm is to position the wrist and which then is
required to orient the end effector.
The robot movements are broadly classified into two main categories,
namely
(i) arm and body motions (ii) wrist motions
The individual joint motions associated with these two categories are
also referred to as the degrees of freedom
The first three axes of the robot are referred to as the major axes.
The position of the end-effector of the robot is determined by the
position of the major axes.
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Similarly three more axes associated with the wrist, are called minor
axes and are used to establish the orientation of the tool or the
gripper at wrist
Degrees of freedom (DOF) is a term used to describe a robot’s freedom of motion
in three dimensional space
specifically, the ability to move forward and backward, up and down, and to the left and to the
right
For each degree of freedom, a joint is required.
A robot requires minimum six degrees of freedom to be completely
versatile.
The human hand has 22 degrees of freedom
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The number of degrees of freedom defines the robot‟s configuration
For example, many simple applications require movement along three
axes: X, Y, and Z.
Thus a minimum of six axes are required to achieve any desirable
position and orientation in the robot’s work volume or work envelop
or workspace.
The locus of the points in the three dimensional
space that can be reached by the wrist by the
various combinations of the movements of the
robot joints from base up to wrist, is called the
gross work envelop of the robot.
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The rigid members connected at the joints of the robot are called
links.
In the link-joint-link chain, the link closest to the base is referred to
as the input link.
The output link is the one which moves with respect to the input
link.
There are basically two types of joints commonly used in industrial
robots, which are:
Prismatic or linear joints,(P) which have sliding or linear
(translational) motion along an axis.
Revolute ,(R) : which exhibits the rotary motion about an axis.
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Based on the physical configuration or the combination of the revolute
or prismatic joints for the three major axes, a particular geometry
of the work envelop is achieved.
Cartesian Coordinate robots:
3P (PPP)
The three joints corresponds to the notation for the moving the wrist up and down, in
and out, and back and forth .
Robot Configurations
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Cartesian Coordinate robots:
3P (PPP)
The three joints corresponds to the notation for the moving the wrist up and down, in
and out, and back and forth .
Thus the work envelop/ work volume generated by this robot is a rectangular box.
example: the gantry robot:
High accuracy but low dexterity
Large work volume, handle large dimension, and heavy weight
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Cylindrical Robots:
RPP or R2P: first prismatic joint replaced with Revolute: Cylindrical robot
commonly used for: handling at die-casting machines, assembly operations,
handling machine tools, and spot welding operations.
As there is always some minimum radial position, the work envelop is actually the
volume between two concentric cylinders.
• 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
• can't reach above itself.
• linear axes is hard to seal.
• won‟t reach around obstacles.
• exposed drives are difficult to cover
from dust and liquids.
Advantage:
Disadvantage:
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Spherical Robot:
RRP or 2RP: If second joint of cylindrical coordinate robot is replaced with
revolute joint (RRP) this produces spherical coordinate robot.
As there is always some minimum radial position, the work envelop is actually the
volume between two concentric spheres.
Here the first revolute joint swings the arm back and forth about a
vertical base axis,
the second revolute joint moves the arm up and down about the horizontal
shoulder axis,
the prismatic joint moves the wrist radially in and out
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Spherical Robot:
Commonly used for: material handling at die casting
or fettling machines, handling machine tools and for arc/spot welding etc.
Large working envelope.
Two rotary drives are easily sealed against liquids/dust
The disadvantages are:
Complex coordinates more difficult to visualize,
control, and program.
Exposed linear drive.
Low accuracy
The advantages are:
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RRP: SCARA
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For SCARA robot all axes are vertical/parallel
It gives rigidity in vertical direction and compliance in horizontal axis.
Commonly used for: pick and place work, and assembly operation with high
working speeds.
RRP: SCARA
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Articulated Robot
In articulated coordinate robot all joints are revolute joint (RRR).
It closely resembles the anatomy of human arm
First revolute joint swings robot
back and forth about vertical
base axis.
Second joint pitches the arm
up and down about horizontal shoulder axis.
Third joint pitches the forearm up and down
about horizontal elbow axis
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Articulated Robot
In articulated coordinate robot all joints are revolute joint (RRR).
Commonly used for: assembly operations, welding, weld sealing, spray
painting, and handling at die casting or fettling machines.
• Main advantages :
All rotary joints allows
for maximum flexibility
All joints can be sealed from
the environment
• The main disadvantages are:
Extremely difficult to visualize,
control, and program these robots.
Restricted volume coverage.
Low accuracy
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Summary
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Robot Classification According to
Control Methods
Non servo control
Servo control
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Robot Classification According to
Control Methods
Non Servo Control
• Implemented by setting limits or mechanical stops for each joint
and sequencing the actuation of each joint to accomplish the cycle
• end point robot, limited sequence robot, bang-bang robot
• No control over the motion at the intermediate points, only end
points are known
• Programming accomplished by
– setting desired sequence of moves
– adjusting end stops for each axis accordingly
– the sequence of moves is controlled by a “sequencer”, which uses
feedback received from the end stops to index to next step in
the program
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• Low cost and easy to maintain, reliable
• relatively high speed
• repeatability of up to 0.01 inch
• limited flexibility
• typically hydraulic, pneumatic drives
Non Servo Control
Robot Classification According to Control
Methods
• Point to point Control
• Continuous Path Control
Closed Loop control used to monitor position, velocity (other variables) of
each joint
Servo Control
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Point-to-Point Control
• Only the end points are programmed, the path used to connect
the end points are computed by the controller
• user can control velocity, and may permit linear or piece wise
linear motion
• Feedback control is used during motion to ascertain that
individual joints have achieved desired location.
• Often used hydraulic drives, recent trend towards servomotors
• loads up to 500lb and large reach
• Applications
– pick and place type operations
– palletizing
– machine loading
Servo Control
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Continuous Path Controlled
• In addition to the control over the endpoints, the path
taken by the end effector can be controlled
• Path is controlled by manipulating the joints
throughout the entire motion, via closed loop control
• Applications:
– spray painting, polishing, grinding, arc welding
Servo Control
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ROBOT PROGRAMMING
Typically performed using one of the
following
– On line
• teach pendant
• lead through programming
– Off line
• robot programming languages
• task level programming
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Use of Teach Pendant
• hand held device with switches used to control the
robot motions
• End points are recorded in controller memory
• sequentially played back to execute robot actions
• trajectory determined by robot controller
• suited for point to point control applications
• Easy to use, no special programming skills required
• Useful when programming robots for wide range of
repetitive tasks for long production runs
• RAPID
ROBOT PROGRAMMING
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Lead Through Programming
• lead the robot physically through the required
sequence of motions
• trajectory and endpoints are recorded, using a
sampling routine which records points at 60-80 times
a second
• when played back results in a smooth continuous
motion
• large memory requirements
ROBOT PROGRAMMING
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Programming Languages
Motivation
need to interface robot control system to external sensors, to
provide “real time” changes based on sensory equipment
computing based on geometry of environment
ability to interface with CAD/CAM systems
meaningful task descriptions
off-line programming capability
Large number of robot languages available
AML, VAL, AL, RAIL, RobotStudio, etc. (200+)
Each robot manufacturer has their own robot
programming language
No standards exist
Portability of programs virtually non-existent
ROBOT PROGRAMMING
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Drive Technology
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Mechanical systems
 Devices which can be considered to be motion converters in that they
transform motion from one form to some other required form.
– Eg: Transform linear motion into rotational motion and vice versa.
 Mechanical elements can include the use of linkages, cams, gears,
rack-and-pinion, chains, belt drives, etc.
– E.g.: rack-and-pinion can be used to convert rotational
motion to linear motion.
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Mechanical systems
 Others function:
– Force amplification – given by levers.
– Change of speed – given by gears.
– Transfer of rotation about one axis to rotation about
another – timing belt.
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• Gear trains are mechanisms which are very widely used:
 to transfer and transform rotational motion.
 used when a change in speed or torque of a rotating device is
needed.
 Transmits rotating motion from one parallel shaft to another
• For example, the car gearbox enables the driver to match the speed
and torque requirements of the terrain with the engine power
available.
(a) Parallel gear axes, (b) axes inclined to one another, (c) axial teeth,
(d) helical teeth, (e) double helical teeth
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Gears

…Gears
• Two meshed gears.
• Gear ratio,
Number of teeth is proportional to
the diameter of the wheel
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•Can multiply torque and speed
•Can reduce torque and speed
•Same size & number of teeth = no
change in output
•Equal size gears create equal output
•Small drive gear to larger driven gear
= driven gear speed decreases.
•Larger drive gear to smaller driven
gear = driven gear speed increases

…Gears
 Gear trains – a series of intermeshed gear wheels.
 Simple gear train – used for a system where each shaft carries only one gear
wheel.
 Ratio of the angular velocities,
Example: Consider the compound gear train above, driver (A) has 15 teeth,
B has 30 teeth and C has 36 teeth. Find the overall gear ratio.
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…Gears
Rotational to translational motion
 Two intermeshed gears with one having a base circle of infinite radius.
 Such gear can be used to transform either linear motion to rotational
motion or rotational motion to linear motion.
Eg: The rack-and-pinion.
 Linear velocity,
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Distance moved parallel to the screw axis

…Gears
 Type of gears
Spur gears
Helical Gears
Idler Gears
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Bevel gears
Internal gear teeth

Rack & pinion
Example :A rack with 100 teeth per metre is meshed to a pinion with
10 teeth. If the pinion rotates once how far does the rack move?
How many revolutions does it take to move the rack from one end
to the other? The rack is 1m long.
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Rack is 1m long with 100T, so each tooth is worth 1000/100 = 10mm .
This value is known as the Tooth Pitch of the rack.
Thus if pinion rotates once(10teeth), then ,
Solution
Since the rack is 1m (1000mm) long then it will take 1000mm/100mm = 10
revolutions to move from one end to the other. (1 rev of pinion = 100mm)
10 10 100
mm mm
 

Hydraulic Actuators
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The term ‘hydraulics’ refers to the power
produced in moving liquids.
Modern hydraulic systems are defined as;
The use of confined liquids to transmit power, multiply
force or produce motion efficiently.
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Fluid actuators

Pascal’s Law
• The French mathematician & philosopher, Blaise Pascal, discovered
that liquids cannot be compressed.
• His work on hydraulics led to him publishing the following law
concerning confined fluids;
“A change in the pressure of an enclosed incompressible fluid is
conveyed undiminished to every part of the fluid and to the
surfaces of its container."
• In other words, if a pressure is applied on a confined fluid,
this pressure is transmitted in all directions with equal force on
equal areas.
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Basic Hydraulic System
 A ‘Basic’ hydraulic system provides a mechanical advantage
similar to that of a simple lever
By using cylinders of different sizes a Multiplication of Forces can
be achieved
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2 2 2
F P A

1 1 1
F PA

2
2 1
1
A
F F
A
 

Typical Hydraulic System
Typically, a hydraulic system will consist of;
– The Hydraulic Fluid
– A Reservoir (tank)
– A Hydraulic Pump
– Hydraulic Fluid Lines
– A number of Hydraulic Valves
– A number of Hydraulic Actuators (cylinders etc)
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Typical Layout
The diagram below shows a typical layout of components in a
Hydraulic System.
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Hydraulic system components
The diagram below shows the main components in a
Hydraulic System.
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Control system for a typical Hydraulic system
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Hydraulic Fluid
•The fluid used within the hydraulic system can be almost any liquid.
•However, the most common hydraulic fluids contain specially compounded
petroleum oils.
– These lubricate and protect the system components from corrosion.
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Reservoir
•The reservoir is no more than a tank that acts as a storehouse for the
fluid.
•The reservoir also acts as a heat dissipater – ensuring that the oil remains
at the optimum temperature.
– If the oil gets too hot, it‟s properties change and the fluid will become more
viscous.
– If the properties of the hydraulic fluid change, this can affect the
responsiveness of the system.

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•The hydraulic pump allows the conversion of mechanical energy into
hydraulic energy by forcing the hydraulic fluid, under pressure, from the
reservoir, through a filter into the system.
•The type of pump used will be dependent on the application, but „Gear
Pumps‟, „Vane Pumps‟ and „Piston Pumps‟ are the three types of pumps
typically utilised.
The Hydraulic Pump
Hydraulic Fluid Lines
•The hydraulic fluid lines transport the hydraulic fluid to and from the
pump through to all the components of the hydraulic system.
•These lines can be rigid metal tubes, or flexible hose assemblies.
•The fluid lines can transport fluid either under pressure or via vacuum (i.e.
suction).

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Hydraulic Selector Valves
The hydraulic selector valves are used to control the pressure, direction and flow rate
of the hydraulic fluid within the hydraulic system.
There are a number of different types of selector valve in use – a common type is the
Open Centre Spool Valve.
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•The hydraulic actuator converts hydraulic energy into mechanical energy
to do work.
•The actuators usually take the form of hydraulic cylinders with a piston
that allows the hydraulic ram to move in and out.
Hydraulic Actuators

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Special Problems
The extreme flexibility of hydraulic systems present a number
of problems
– Since hydraulic fluid has no shape, they must be positively confined
throughout the entire system.
– Special consideration to the structural integrity of the system must
be given – i.e. Strong pipes and containers
– Leaks must be prevented – a particular problem with the high
pressures involved.
– The constant movement of the fluid in the system results in friction
within the fluid and hence a reduction in efficiency.
– Foreign matter must not be allowed to accumulate in the system.
– Chemical action may cause corrosion of the system components
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Pneumatic Systems
Pneumatic systems work in a very similar way to that of hydraulic
systems.
 It is very similar to hydraulic system, but power-to-weight ratio is much
lower than hydraulic system
The major difference is that in pneumatic systems, high pressure air is
used instead of hydraulic fluid.
– This is because air is much more compressible than fluid and it is much
easier to store the pressure, using reservoirs.
This can give a reserve of power for short bursts of very heavy
operation, or for emergency use if the system fails.
In an airframe, a pneumatic system can be used in place of a hydraulic
system
 Variety of Actuation mechanisms available
• Cylinders
• Grippers
• Motors
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Typical Pneumatic System
Like the hydraulic system, the layout and complexity of a pneumatic
system will vary based on it‟s primary function, but the principles and
components of the system will be the same.
•Typically, a pneumatic system will consist of;
– A Storage Cylinder – for the compressed air
– Pressure Gauges
– Pressure Valves – Non-Return, Reducing, Maintaining
– Pneumatic Air Lines
– A number of Pneumatic Selector Valves
– A number of Pneumatic Actuators
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Typical Layout
The diagram below shows a typical layout of components in a Pneumatic
System.
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Basic Pneumatic System
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Disadvantages of Pneumatics
Due to, the compressibility of air:
–The response depends strongly on the load
–The rate of movement depends strongly on the load
–The position of systems cannot be controlled with any degree of
accuracy.
Relative inefficiency in transmitting power when compared with
Hydraulic system(b/c energy is lost in compressing the air)
All these components take up quite a bit of valuable space within a
robot.
No weight advantage if only one cylinder used (still need compressor,
reservoir, pressure sensors, regulator)
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Advantage of Pneumatics
• Weight
– Cylinders much lighter than motors
• Simple
– Much easier to mount than motors
– Much simpler and more durable than rack and pinion for
linear motion
• Clean (food industry)
• Fast on/off type tasks
• No return lines needed
• Big forces with elasticity
• No leak problems
• No burnout
– Cylinders can be stalled indefinitely without damage
• Adaptable infrastructure
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Key components of Hydraulic and Pneumatic
• Pump/Compressor
• Pressure regulator
• Valve
• Solenoid
• Actuator
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Valves
1. Direction control valves
2. Pressure control valves
3. Process control valves

Ports are labeled by a number
or letter:
1 (P) : pressure supply
3(T) : hydraulic return
3/5 or R/S : pneumatic exhaust
ports
2/5 or B/A : output ports
Valve Symbols:
Control methods
Valve connections
Valves with controls indicated
Finite position valve usually specified as
“x/y valve”
x: number of ports (sum of inlets and
outlets)
y: number of positions
4/3 valve: 4 ports and 3 positions
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Electrical Actuators
 Electric motors
• DC servo motors
• AC motors
• Stepper motors
• Solenoids
• Relays
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 Advantages:
 Widespread availability of power supply.
 Basic drive element is lighter than fluid power.
 High power conversion efficiency.
 No pollution
 accuracy + repeatability compared to cost.
 Quiet and clean
 Easily maintained and repaired.
 Components are lightweight.
 Drive system is suitable to electronic control
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 Disadvantages:
 Requires mechanical transmission system.
 Adds mass and unwanted movement.
 Requires additional power + cost.
 Not safe in explosive atmospheres.
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DC Motors
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Servomotor
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• A servo motor consists of a
DC motor, reduction gearbox,
positional feedback device and
some form of error correction.
•The speed or position is
controlled in relation to a
positional input signal or
reference signal applied to the
device.

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AC Motors

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Stepper Motors

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Stepper Motors

Example
A stepper motor has a step angle = 3.6°.
1. How many pulses are required for the motor to
rotate through ten complete revolutions?
2. What pulse frequency is required for the motor to
rotate at a speed of 100 rpm (rev/min)?
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Stepper motor vs. Servomotors

Drive Systems Summary
•Hydraulic
Larger Robots
Greater speed & strength
Larger floor space required
Rotary vane actuators for rotary motion
Hydraulic pistons for linear motion
•Electric
Accuracy & repeatability is better
Smaller floor space
Stepper motors or servo motors
Drive train/gear systems for rotational
Pulleys or similar systems for linear motion.
•Pneumatic
Smaller robots with fewer DoF
Pick-and-place with fast cycles
Pneumatic pistons
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Current State of Actuators
All three types of actuators are in use today
– Electric actuators are the type most commonly
used
– Hydraulic and pneumatic systems allow for
increased force and torque from smaller motor
There are some dual function actuators
– i.e. rotation and translation
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Selection criteria
For robot applications –
Positioning accuracy, reliability, speed of operation, cost,
etc.
Electric is clean + Capable of high precision
Electronics is cheap but more heat
Pneumatics are not for high precision for continuous path
Hydraulics can generate more power in compact volume
Capable of high torque + Rapid operations
Power for electro-hydraulic valve is small but expensive
All power can be from one powerful hydraulic pump located at distance
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Thumb Rule for Motor Selection
Rapid movement with high torques (>
3.5 kW): Hydraulic actuator .
< 1.5 kW (no fire hazard): Electric
motors .
1-5 kW: Availability or cost will
determine the choice
Simple Calculation
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Industrial Application
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Material handling
Material transfer
Machine loading and/or
unloading
Spot welding
Continuous arc welding
Spray coating
Assembly
Inspection
Assembly manipulator

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Loading/unloading parts to/from the machines
 Unloading parts from die-casting machines
 Loading a raw hot billet into a die, holding it during forging and unloading it
from the forging die
 Loading sheet blanks into automatic presses
 Unloading molded parts formed in injection molding machines
 Loading raw blanks into NC machine tools and unloading the finished
parts from the machines

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Single machine robotic cell applications include:
 The incoming conveyor delivers the parts to the fixed position
 The robot picks up a part from the conveyor and moves to the
machine.
 The robot loads the part onto the machine
 The part is processed on the machine
 The robot unloads the part from the machine
 The robot puts the part on the outgoing conveyor
 The robot moves from the output conveyor to the input
conveyor
Multi-machine robotic cell application:
Two or three CNC machines are served by a robot.
The cell layout is normally circular.

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Spot welding quickly became a primary application for robots as
these jobs were particularly exhausting and hazardous for
workers.
A typical car body welding line from 1985 is displayed.
The car model shown is a French Citroën CX
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Car body assembly: A car body assembly usually follows the
illustrated steps: Stamping of the metal sheet into plates, fixing and
alignment of the plates on trays, spot welding, painting the car body, and
final assembly of the car body (doors, dashboard, windscreens, power-train
seats, and tires). Car factories can host well over 1000 robots working two
to three shifts per day

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Robot specification
But in addition to classification, there are several additional
characteristics :
(i) Number of axes
(ii) Load carrying capacity (kg)
(iii) Maximum speed (mm/sec)
(iv) Reach and stroke (mm)
(v) Tool orientation (deg)
(vi) Precision, accuracy and Repeatability of movement (mm)
(viii) Operating environment
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End
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