UNIT 1

FUNDAMENTALS OF ROBOTS

Sukantho Sikder
Electronics Department
 Robotics
History
Three Laws of Robotics:
1. A robot may not injure a human being, or, through
inaction, allow a human being to come to harm.
2. A robot must obey the orders given it by human
beings except where such orders would conflict
with the First Law.
3. A robot must protect its own existence as long as
such protection does not conflict with the First or
Second Law.

2
 Robotics Timeline
• 1922 Czech author Karel Capek wrote a story called
Rossum’s Universal Robots and introduced the
word “Rabota”(meaning worker)
• 1954 George Devol developed the first
programmable Robot.
• 1955 Denavit and Hartenberg developed the
homogenous transformation matrices
• 1962 Unimation was formed, first industrial
Robots appeared.
• 1973 Cincinnati Milacron introduced the T3 model
robot, which became very popular in industry.
• 1990 Cincinnati Milacron was acquired by ABB
Robot
Anatomy
 ROBO
• Defined by Robotics T
Industry Association (RIA) as
– a re-programmable, multifunctional manipulator
designed to move material, parts, tools or
specialized devices through variable programmed
motion for a variety of tasks

• Possess certain anthropomorphic characteristics

– mechanical arm
– sensors to respond to input
– Intelligence to make decisions
 Robot
Accessories
A Robot is a system, consists of the following elements, which
are integrated to form a whole:

• Manipulator / Rover : This is the main body of the Robot

and consists of links, joints and structural elements of the
Robot.

• End Effector : This is the part that generally handles objects,

makes connection to other machines, or performs the required
tasks.
It can vary in size and complexity from a endeffector on the space
shuttle to a small gripper
 Accessorie
s
• Acutators : Actuators are the muscles of the manipulators.
Common types of actuators are servomotors, stepper
motors, pneumatic cylinders etc.

• Sensors : Sensors are used to collect information about the

internal state of the robot or to communicate with the
outside environment. Robots are often equipped with
external sensory devices such as a vision system, touch and
tactile sensors etc which help to communicate with the
environment

• Controller : The controller receives data from the

computer, controls the motions of the actuator and
coordinates these motions with the sensory feedback
information.
 The Advent of Industrial
Robots
Motivation for using robots to perform task which
would otherwise be performed by humans.

• Safety
• Efficiency
• Reliability
• Worker Redeployment
• Cost reduction
 Main Components of Industrial
Robots

– Arm or
Manipulator
– End effectors
– Drive Source
– Control Systems
– Sensors
 Arm or
Manipulator
• The main anthropomorphic element of a robot.
• In most cases the degrees of freedom depends on the arm
•The work volume or reach mostly depends on the functionality
of the Arm
 End
Effectors
Device attached to the robot’s wrist to perform a specific task

Grippers
– Mechanical Grippers
– Suction cups or vacuum
cups
– Magnetized grippers
– Hooks
– Scoops (to carry fluids)
 End
Effectors
Device attached to the robot’s wrist to perform a specific task

Tools
– Spot Welding gun
– Arc Welding tools
– Spray painting gun
– Drilling Spindle
– Grinders, Wire
brushes
– Heating torches
 Sensors in
robotics
Types of sensors :
–Tactile sensors (touch sensors, force sensors, tactile array
sensors)
–Proximity and range sensors (optical sensors, acoustical
sensors, electromagnetic sensors)
–Miscellaneous sensors (transducers and sensors which sense
variables such temperature, pressure, fluid flow,
thermocouples, voice sensors)
– Machine vision systems
 Sensors in
Uses of sensors:
robotics
– Safety monitoring
– Interlocks in work cell control
– Part inspection for quality control
– Determining positions and related information about
objects
 Sensors in
robotics
Desirable features of
sensors:
Accuracy
Operation range
Speed of
response
Calibration
Reliability
Cost and ease of
operation
 Work Envelope
•
concept
Depending on the configuration and size of the
links and wrist joints, robots can reach a collection
of points called a Workspace.

• Alternately Workspace may be found empirically,

by moving each joint through its range of motions
and combining all space it can reach and
subtracting what space it cannot reach
 WRIS
T
• typically has 3 degrees of freedom
– Roll involves rotating the wrist about the arm
axis
– Pitch up-down rotation of the wrist
– Yaw left-right rotation of the wrist
• End effector is mounted on the wrist
WRIST
MOTIONS
 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
 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
 Robot
•
Anatomy
Manipulator consists of joints and links
Joint3 Link
Joints provide relative motion
– 3
End of
Links are rigid members between joints
– Arm
Various joint types: linear and rotary
–
Each joint provides a “degree-of-
– Link
freedom” 2
Link
– Most robots possess five or six degrees- 1
of- Joint2
freedom
• Robot manipulator
in the consists of two sections:Joint1
robot's work
– volume
– Body-and-arm
Wrist assembly––for
forpositioning
orientationofofobjects
objectLsink0 Bas
e
 Manipulator
Joints
• Translational motion
– Linear joint (type L)
– Orthogonal joint (type
O)

• Rotary motion
– Rotational joint (type R)
– Twisting joint (type T)
– Revolving joint (type V)
 Joint Notation
Scheme
• Uses the joint symbols (L, O, R, T, V) to
designate joint types used to construct
robot manipulator
• Separates body-and-arm assembly from
wrist assembly using a colon (:)

• Example: TLR : TR

• Common body-and-arm configurations …

 Polar Coordinate
Body-and-Arm
Assembly
• Notation
TRL:

• Consists of a sliding arm (L joint) actuated

relative to the body, which can rotate about
both a vertical axis (T joint) and horizontal axis
(R joint)
 Cylindrical Body-and-Arm
Assembly
• Notation
TLO:

• Consists of a vertical
column, relative to which
an arm assembly is
moved up or down
• The arm can be moved in
or out relative to the
column
 Cartesian Coordinate
Body-and-Arm
Assembly
• Notation LOO:

• Consists of three
sliding joints, two of
which are orthogonal
• Other names include
rectilinear robot and x-y-
z robot
 Jointed-Arm
Robot
• Notation
TRR:
 SCARA
Robot
• Notation VRO
• SCARA stands for
Selectively
Compliant Assembly
Robot Arm
• Similar to jointed-arm
robot except that vertical
axes are used for
shoulder and elbow
joints to be compliant in
horizontal direction for
vertical insertion tasks
 Wrist
• Configurations
Wrist assembly is attached to end-of-arm
• End effector is attached to wrist assembly
• Function of wrist assembly is to orient end effector
– Body-and-arm determines global position of end
effector
• Two or three degrees of freedom:
– Roll
– Pitch
– Yaw
• Notation :RRT
 Exampl
e
• Sketch following manipulator
configurations
• (a) TRT:R, (b) TVR:TR, (c) RR:T.
Solution R
R

: T R
R T
R
R T V

T T

(a) TRT:R (b) TVR:TR (c) RR:T

 Programming
Robots
• Manua
l Cams, stops etc
•Walkthrough (Lead-through)
Manually move the arm, record to
memory

• Manual teaching
Teach pendant

• Off-line programming
Similar to NC part
programming
VAL, RAPT
 Application
s
• Material Handling/Palletizing
• Machine Loading/Unloading
• Arc/Spot Welding
• Water jet/Laser cutting
• Spray Coating
• Gluing/Sealing
• Investment casting
• Processing operations
• Assembly
• Inspection
Performance Specifications of
Industrial Robots
• Size of the working envelope • Motion control
– path control
• Precision of movement
– velocity
– Control resolution
control
– Accuracy
– Repeatability • Types of drive motors
– hydraulic
• Lifting capability
– electric
• Number of robot axes – pneumatic
• Speed of movement
– maximum speed
– acceleration/deceleration
time
 Work
Volume
Spatial region within which the end
of the robot’s wrist can be
manipulated

Determined by
– Physical configurations
– Size
– Number of axes
– The robot mounted position (ove rhead gantry,
mounted, floor mounted, on wall-
tracks )
– Limits of arm and joint
configurations
– The addition of an end-effector
can move or offset the
entire work volume
 Spatial
Smallest increment ofResolution
motion at the wrist end that can be controlled by the robot

Depends on the position control system, feedback measurement, and

mechanical accuracy
 Accurac
ya target point in the work volume
Capability to position the wrist at

• One half of the distance between two adjacent resolution

points
• Affected by mechanical Inaccuracies
• Manufacturers don’t provide the accuracy (hard control)
to
 Repeatabilit
Ability to positiony
back to a point that was previously taught

• Repeatability errors form a random variable.

• Mechanical inaccuracies in arm, wrist components
• Larger robots have less precise repeatability values
 Weight Carrying
Capacity
• The lifting capability provided by manufacturer doesn’t include the weight of the
end
effector
• Usual Range 2.5lb-2000lb
• Condition to be satisfied:

Load Capability > Total Wt. of workpiece +Wt. of end effector + Safety
range
 Speed of
Movement
Speed with which the robot can manipulate the end effector

•Acceleration/deceleration times are crucial for cycle time.

•Determined by
– Weight of the object
– Distance moved
– Precision with which object must be positioned
 Motion
Control
•Path control - how accurately a robot traces a given path (critical for gluing, painting,
welding applications);
•Velocity control - how well the velocity is controlled (critical for gluing, painting
applications)
• Types of control path:
-point to point control (used in assembly, palletizing, machine loading); - continuous
path control/walkthrough (paint spraying, welding).
- controlled path (paint spraying, welding).
 Degrees of
Freedom
• Degree of freedom - one joint one degree of freedom
• Simple robots - 3 degrees of freedom in X,Y,Z axis
• Modern robot arms have up to 6 degrees of freedom
• XYZ, Roll, Pitch and Yaw
• The human arm can be used to demonstrate the
degrees of freedom.

• Crust Crawler- 5 degrees of

freedom
 Robot Applications
(Configurations/Characteristi
cs)
SCARA Robot
Characteristics:
(Selective Compliance Assembly Robot
•Repeatability: < 0.025mm (high)
Arm)
•No. of axes: min 4 axes
•Vertical motions smoother, quicker, precise (due to
dedicated vertical axis)
•Good vertical rigidity, high compliance in the
horizontal plane.
•Working envelope: range < 1000mm
•Payload:10- 100 kg
•Speed: fast 1000-5000mm/s

Applications:
•Precision, high-speed, light assembly
 Robot Applications
(Configurations/Characteristi
cs)Robot
Cylindrical Coordinate

Characteristics:
•Wide range of sizes
•Repeatability: vary 0.1-0.5mm
•No. of axes: min 3 arm axes (2 linear)
•Working envelope: typically large (vertical stroke
as
long as radial stroke)
• The structure is not compact.
•Payload: 5 - 250kg
•Speed: 1000mm/s, average
•Cost: inexpensive for their size and payload

Applications:
•Small robots: precision small assembly tasks
•Large robots: material handling, machine loading/unloading.
 Robot Applications
(Configurations/Characteristi
Vertical Articulatedcs)
Arm Robot

Characteristics:
•Repeatability: 0.1-0.5mm (large sizes not
adequate for precision assembly)
•No. of axes: 3 rotary arm-axes, 2-3 additional
wrist axis (excellent wrist articulation)
•Working envelope: large relative to the size,
Structure compact, but not so rigid
•Payload: 5-130kg
•Tool tip speed: fast 2000mm/s

Applications: Welding, painting, sealing, deburring, and material

handling
 Robot Applications
(Configurations/Characteristi
cs)
Spherical Coordinate Robot

Characteristics:
•Repeatability: poor 0.5-1mm
•No. of axes: 3 arm-axes (1 linear radial), 1-
2 additional wrist-axes.
•Working envelope: large vertical envelope
relative to the unit size
•Payload: 5-100 kg
•Speed: low (linear motions are not smooth
and accurate- require coordination of multiple
axes)

Applications: Material handling, spot welding, machine

loading
 Robot Applications
(Configurations/Characteristi
cs)
Cartesian Coordinate Robot

Characteristics:
•Repeatability: high (0.015-0.1)
•No. of axes: 3 linear arm-axis,
•Working envelope:relative large •Payload:5-
100kg
•Speed: fast

Applications: Precise assembly, arc welding, gluing, material

handling
 Robot Applications
(Configurations/Characteristi
cs)
Gantry
Robot
Characteristics:
•Repeatability: 0.1-1mm
•No. of axes: 3 linear traverse-axes, 1-3
additional wrist axes
•Working envelope: very large
•Payload: vary function of size, support very
heavy
10-1000kg
•Speed: low for large masses

Applications:
Handling very large parts, moving material on long distances, welding,
gluing.
 Types of
•
•
robots
Industrial robots(welding, handling, painting, AGV)
Domestic robots(vacuum cleaners, surveillance)
• Medical robots(surgery)
• Service robots(data gathering, lifting)
• Military robots(bomb disposal, transportance)
• Entertainment robots(toy, motion simulator)
• Space robots(space station)
• Hobby and competition robots
• Explorer robots(underground mine, walking
undersea)
• Laboratory robots(pharmaceutical robots)
• Sequence robots
• Playback robots
Thank you
 UNIT
II
ROBOT DRIVE
SYSTEMS AND END
EFFECTORS

R.PREM
KUMAR AP –
MECH KIT ,
There are basically Four types of power
sources
1. Pneumatic drive
• Preferred for smaller robots
• Less expensive than electric or
hydraulic robots
• Suitable for relatively less degrees of
freedom design
• Suitable for simple pick and place application
• Relatively cheaper

2004 3
Pneumatic
drive
2. Hydraulic
drive
• Provide fast movements
• Preferred for moving heavy parts
• Preferred to be used in
explosive environments
• Occupy large space area
• There is a danger of oil leak to
the shop floor

2004 5
Hydraulic
drive
3. Electric
drive
• Slower movement compare to the
hydraulic robots
• Good for small and medium size robots
• Better positioning accuracy and
repeatability
• Stepper motor drive: open loop control
• DC motor drive: closed loop control
• Cleaner environment
• The most used type of drive in industry

2004 7
Electric
drive
4. Mechanical
drives
• When the various driving methods like hydraulic,
pneumatic, electrical servo motors and stepping
motors are used in robots, it is necessary to get the
motion in linear or rotary fashion.

• When motors are used, rotary motion is converted

to linear motion through rack and pinion gearing,
lead screws, worm gearing or bail screws.
 Mechanical
drives
Rack and Pinion Movement:
• The pinion is in mesh with rack (gear of
infinite radius). If the rack is fixed, the pinion will
rotate.
• The rotary motion of the pinion will be converted to
linear motion of the carriage.
Ball
•Screws:
Sometimes lead screws rotate to drive the nut along
a track. But simple lead screws cause friction and
wear, causing positional inaccuracy.
• Therefore ball bearing screws are used in robots as
they have low friction. The balls roll between the
nut and the screw.
• A cage is provided for recirculation of the balls. The
rolling friction of the ball enhances transmission
efficiency to about 90%.
Gear
Trains:
• Gear trains use spur, helical and
gearing. A reduction of worm
torque and angular velocityspeed,
are possible.
change of
• Positional errors are caused due to backlash
in the gears.
 Moments and
Forces
• There are many forces acting about a robot
• Correct selection of servo - determined by required
torque
• Moments = Force x Distance
• Moments = Load and robot arm
• Total moment calculation
• Factor of safety- 20%
 Actuator
s
Actuators – Converts some form of energy to mechanical
work . Motors - Control the movement of a robot.
Identified as Actuators there are three common types

• DC Motor
Servo
• Stepper
moto
Motor r

• Servo motor
 DC
MOTORS
• Most common and cheapest
• Powered with two wires from source
• Draws large amounts of current
• Cannot be wired straight from a Peripheral Interface
Controller
• Does not offer accuracy or speed control
STEPPER
MOTORS
• Stepper has many electromagnets
• Stepper controlled by sequential
turning on and off of magnets
•Each pulse moves another step,
providing a step angle
• Example shows a step angle of
90°
• Poor control with a large angle
•Better step angle achieved with the
toothed disc
Stepper motor
operation
Step
1
Stepper motor
operation
Step
2
Stepper motor
operation
Step
3
Stepper motor
operation

Step
4
 Stepper
Motor
• 3.6 degree step angle => 100 steps per revolution
• 25 teeth, 4 step= 1 tooth => 100 steps for 25teeth
• Controlled using output Blocks on a Peripheral Interface Controller
• Correct sequence essential
• Reverse sequence - reverse motor

DISADVANTAGES
• Low efficiency - Motor draws substantial power regardless of
load.
• Torque drops rapidly with speed (torque is the inverse of speed).
• Low accuracy.
• No feedback to indicate missed steps.
• Low torque to inertia ratio. Cannot accelerate loads very rapidly.
• Motor gets very hot in high performance configurations.
• Motor is audibly very noisy at moderate to high speeds.
• Low output power for size and weight.
 SERVO
MOTORS
• Servo offers smoothest control
• Rotate to a specific point
• Offer good torque and control
• Ideal for powering robot arms etc.

• Degree of revolution is limited

• Uses Encoders for feedback
• Not suitable for applications which
require continuous rotation
 Servo Motors
Operation
• Pulse Width Modulation (0.75ms to 2.25ms)
• Pulse Width takes servo from 0° to 150° rotation
• Continuous stream every 20ms
• Pulse width and output pin must be set to the
controller
• Pulse width can also be expressed as a variable
 AC SERVO AND DC
SERVO
• There are two types of servo motors, AC
servos and DC servos.
• The main difference between the two motors
is their source of power.
• AC servo motors rely on an electric outlet,
rather than batteries like DC servo motors.
• While DC servo motor performance is
dependent only on voltage.
• AC servo motors are dependent on
both frequency and voltage.
 Open and Closed Loop
Control
All control systems contain three
elements:
(i) The control
(ii) Current Amplifiers
(iii) Servo Motors

• The control is the Brain - reads instruction

• Current amplifier receives orders from brain and
sends required signal to the motor
• Signal sent depends on the whether Open or Closed
loop control is used.
 Open Loop
Control
For Open Loop Control:
• The controller is told where the output device needs to
be
• Once the controller sends the signal to motor it does not
receive feedback to known if it has reached desired
position
• Open loop much cheaper than closed loop but less
accurate
 Closed Loop
Control
• Provided feedback to the control unit telling it the
actual position of the motor.
• This actual position is found using an encoder.
• The actual position is compared to the desired.
• Position is changed if necessary
 The
•Encoders give the controlEncoder
unit information as to the actual
position of the motor.
•Light shines through a slotted disc, the light sensor counts
the speed and number of breaks in the light.
•Allows for the calculation of speed, direction and
distance travelled.
 End
Effectors
Correct name for the “Hand” that is attached to the end of
robot

End Effector

• Used for grasping, drilling, painting, welding, etc.

• Different end effectors allow for a standard robot
to perform numerous operations.
• Two different types - Grippers as EE & Tools as
EE
 End
Effectors
Grippers : Mechanical, Hydraulic, Magnetic , Pneumatic etc

Tools : Tools are used where a specific operation needs to

be carried out such as welding, painting drilling etc. - the
tool is attached to the mounting plate.

Mechanical:
• Two fingered most common, also multi-fingered available
• Applies force that causes enough friction between object

to allow for it to be lifted

• Not suitable for some objects which may be delicate /
brittle
Mechanical
Grippers
 Pneumatic
• Suction cupsGrippers
from plastic or rubber
• Smooth even surface required
•Weight & size of object determines size
and number of cups
 Vacuum
grippers
• It also called as suction cups,
can be used as gripper device
for handling certain type of
objects and it made up of with
rubber and soft plastic.

• The usual requirements on the

objects to be handled are that
they be flat, smooth, and
clean.
 Magnetic Grippers
• Ferrous materials required
• Electro and permanent magnets
used
 Magnetic
•
grippers
Variations in part size can be tolerated
• Pickup times are very fast
• They have ability to handle metal parts with holes
• Only one surface is required for gripping
• Magnetic grippers can use either electromagnets or
permanent magnets.
• Electromagnetic grippers are easier to control, but require
a source of dc power and an appropriate controller.
• Permanent magnets do not require an external power and
hence they can be used in hazardous and explosive
environments, because there is no danger of sparks
which might cause ignition in such environments.
 Adhesive
• Grippers
It uses adhesive substance to grasping action on fabrics and
light weight materials.
• One of the potential limitation of an adhesive gripper is that
the adhesive substance loses its tackiness on repeated usage.
• To overcome the limitation, the adhesive material is loaded in
the form of a continuous ribbon into a feeding mechanism that
is attached to the robot wrist.
 2 Fingers and 3 Fingers
Gripper

THREE
FINGERS

TWO
FINGERS
 Hooks , Scoops as
• HooksGrippers
can be used to handle containers of parts and to
load and unload parts hanging from overhead conveyors.
• Scoops can be used to handle certain materials in liquid or
powder form.
 Tools as End
Effectors

DRILLIN
G
PAINTIN
G

WELDIN
External and Internal
Grippers
 Selection and Design
• Considerations
The industrial robots use grippers as an end
effector for picking up the raw and finished
work parts.
• A robot can perform good grasping of objects
only when it obtains a proper gripper
selection and design.
• Therefore, Joseph F. Engelberger, who is
referred as Father of Robotics has described
several factors that are required to be
considered in gripper selection and design.
 Selection and Design
• Considerations
The gripper must have the ability to reach the surface of a
work part.
• The change in work part size must be accounted for providing
accurate positioning.
• During machining operations, there will be a change in the
work part size. As a result, the gripper must be designed to
hold a work part even when the size is varied.
• The gripper must not create any sort of distort and scratch in
the fragile work parts.
• The gripper must hold the larger area of a work part if it has
various dimensions which will certainly increase stability and
control in positioning.
 Selection and Design
• Considerations
The replaceable fingers can also be employed for holding
different work part sizes by its interchangeability facility.
• Consideration must be taken to the weight of a work part.
• It must be capable of grasping the work parts constantly at
its centre of mass.
• The speed of robot arm movement and the connection
between the direction of movement and gripper position on
the work part should be considered.
• It must determine either friction or physical constriction
helps to grip the work part.
• It must consider the co-efficient of friction between the
gripper and work part.
THANK
YOU
Sensors and Machine vision
system
Robotic
Sensors
Sensors provide feedback to the control
systems and give the robots more flexibility.
Sensors such as visual sensors are useful in
the building of more accurate and
intelligent robots.
The sensors can be classified as follows:

200 2
Sensor Types
A. Based on power requirement:
1.Active: require external power, called excitation
signal, for the operation
2.Passive: directly generate electrical signal in
response to the external stimulus
B. Based on sensor placement:
1. Contact sensors
2. Non-contact sensors
Why do Robots need
sensors?
 Provides “awareness” of surroundings
 What’s ahead, around, “out there”?
 Allows interaction with environment
 Robot lawn mower can “see” cut grass
 Protection & Self-Preservation
 Safety, Damage Prevention
 Gives the robot capability to
goal-seek
 Find colorful objects, seek goals
 Makes robots “interesting”
What can be
sensed?
 Light
 Presence, color, intensity, direction
 Sound
 Presence, frequency, intensity, direction
 Heat
 Temperature, wavelength, magnitude,
direction
 Chemicals
 Presence, concentration, identity, etc.
 Object Proximity
 Presence/absence, distance, bearing, color, etc.
 Physical orientation/attitude/position
 Magnitude, pitch, roll, yaw, coordinates, etc.
 Magnetic & Electric Fields
 Presence, magnitude, orientation
 Resistance
 Presence, magnitude, etc.
 Capacitance
 Presence, magnitude, etc.
 Inductance
 Presence, magnitude, etc.
 Characteristics of

sensor
Range
The range of a sensor indicates the limits between which the
input can vary. For example, a thermocouple for the measurement of
temperature might have a range of 25-225 °C.
 Accuracy
The accuracy defines the closeness of the agreement between
the
actual measurement result and a true value of the measured.
 Sensitivity
Sensitivity of a sensor is defined as the ratio of change in
output value of a sensor to the per unit change in input value that
causes the output change.
 Size, weight and volume.
 linearity
The linearity indicates the relationship between the i/p variations
and o/p variations.
• Resolution
The small change in measured variable and it need minimum
input.
• Response time
It is time to sensor o/p requires to reach certain percentage of
total change.
• Frequency response
Range in which the system ability to resonate to the i/p
remains
high.
• Reliability
Ratio between the no. of times a system operates properly

and
no. of times it is tired.
• Repeatability
Same i/p if the o/p is different each time is to get poor.
 1. Position sensors:
Position sensors are used to monitor the position of
joints.

Information about the position is fed back to the

control systems that are used to determine the
accuracy of positioning.

200 8
Types of position
sensor
 Piezoelectric sensor
 LVDT
 Resolvers
 Optical encoders
 Pneumatic position sensors
 Piezoelectric
sensor
 Piezoelectric sensors: a
microscopic structure is
mounted
crystal on a mass undergoing
acceleration; the piezo crystal is
stressed by acceleration forces
thus producing a voltage

 When an external electric field is

applied to the crystal, the ions in
each unit cell are displaced by
electrostatic forces, resulting in
the mechanical deformation of
the whole crystal.
A piezoelectric sensor is a device that uses the piezoelectric effect to
measure changes in pressure, acceleration, temperature, strain, or force by
converting them to an electrical charge. The prefix piezo- is Greek for
'press' or 'squeeze'.
Application of Piezoelectric
sensor
 LVD
T
 Linear variable differential transformer (LVDT) is a primary
transducer used for measurement of linear displacement.
 It has three coils symmetrically spaced along an insulated tube.
The central coil is primary coil and the other two are secondary
coils.
 Secondary coils are connected in series in such a way that their
outputs oppose each other.
 A magnetic core attached to the element of which displacement is
to be monitored is placed inside the insulated tube.
 Due to an alternating voltage input to the primary coil, alternating
electro-magnetic forces (emf) are generated in secondary coils.
 When the magnetic core is centrally placed with its half portion in
each of the secondary coil regions then the resultant voltage is
zero.
 LVD
T
 LDVT is a robust and precise
device which produce a
voltage output proportional to
the displacement of a ferrous
armature for measurement of
robot joints or end-effectors.
 It is much expensive but
outperforms the potentiometer
transducer.
 A rotary variable differential
transformer (RVDT) can be
used for the measurement of
rotation.
Applications of LVDT sensors

 Measurement of spool position in a wide range of servo valve

applications
 To provide displacement feedback for hydraulic cylinders
 For automatic inspection of final dimensions of products being
packed for dispatch
 To measure distance between the approaching metals
during Friction welding process
 To continuously monitor fluid level as part of leak
detection system
 To detect the number of currency bills dispensed by an ATM
Resolver
sAmeasuring
resolver is a type of rotary electrical transformer used for
degrees of rotation. It is considered an analog device, and
has digital counterparts such as the digital resolver, rotary (or pulse)
encoder.

 It has two stator

windings positioned at
90 degrees.
 The output voltage is
proportional to the sine
or cosine function of the
rotor's angle.
 The rotor is made up of
a winding.
Optical
encoders
It generates pulses proportional to the rotation speed
of the shaft.

light sensor - direction

- resolution
decode
circuitry
light emitter
grating

B A leads B
 The
Encoder
 Encoders give the control unit information as to the actual
position of the motor.
 Light shines through a slotted disc, the light sensor counts the
speed and number of breaks in the light.
Allows for the calculation of speed, direction and distance
travelled.
Pneumatic
sensor
 It uses the principle of a gas nozzle to detect the presence of an
object without any mechanical contact.
 Low pressure air is supplied through angular converging nozzle
surrounding a sensing hole, called o/p port.
 Nozzle may also be of the converging-diverging type.
 Sensing hole communicates through hose with switch chamber,
which contains an elastic diaphragm switch, or other type of
pressure-sensitive switch.
 Nozzle converts some of the energy of the supply air into
kinetic energy
 2. Range sensors:
Range sensors measure distances from a reference
point to other points of importance. Range sensing is
accomplished by means of television cameras or sonar
transmitters and receivers.

200 22
 The distance between the object and the robot hand is
measured using the range sensors Within it is range
of operation.
 The calculation of the distance is by visual
processing.
Range sensors find use in robot navigation
and avoidance of the obstacles in the path.
 In these cases the source of illumination can be light-
source, laser beam or based on ultrasonic
Types of range
sensors
 Triangulation principle
 Structured lighting approach
 Time of flight range finders
 Laser range meters
Triangulation
principle
 This is the simplest of the techniques, which is easily
demonstrated in the Figure.
 The object is swept over by a narrow beam of sharp
light. The sensor focused on a small spot of the object
surface detects the reflected beam of light.
 If ‗8‘ is the angle made by the illuminating source and
‗b‘ is the distance between source and the sensor, the
distance ‗c of the sensor on the robot is given as
Structured lighting
approach
 This approach consists of projecting a light
distortion of the pattern to calculate the range.
pattern the

 The intersection of the sheet with objects in the‘ work space

yields a light stripe which is viewed through a television
camera displaced a distance B from the light source.
 The stripe pattern is easily analyzed by a computer to obtain
range information.
 For example, an inflection indicates a change of surface, and a
break corresponds to a gap between surfaces.
 In this, arrangement, the light source and camera are
placed at the same height, and the sheet of light is
perpendicular to the line joining the origin of the light
sheet and the center of the camera lens.
Laser Ranger
Finder
 Range 2-500 meters
 Resolution : 10 mm
 Field of view : 100 - 180 degrees
 Angular resolution : 0.25 degrees
 Scan time : 13 - 40 msec.
 These lasers are more immune to Dust and
Fog
http://www.sick.de/de/products/categories/safety/
Range
Finder
 Time of Flight
 The measured pulses typically come form ultrasonic, RF
and optical energy sources.
D =v*t
 D = round-trip distance
 v = speed of wave propagation
 t = elapsed time
 Sound = 0.3 meters/msec
 RF/light = 0.3 meters / ns (Very difficult to measure
short
distances 1-100 meters)
 4. Proximity Sensors:
They are used to sense and indicate the presence of an
object within a specified distance without any physical
contact. This helps prevent accidents and damage to
the robot.
 Inductive type sensors
 Hall effect sensors
 Capacitive type sensors
 Ultrasonic sensors
 Optical sensors

200 3
Inductive type
sensors
 The ferromagnetic material brought close to this type of sensor
results in change in position of the flux lines of the permanent
magnet leading to change in inductance of the coil.
 The proximity inductive sensor basically consists of a wound
coil located in front of a permanent magnet encased inside a
rugged housing.
 The lead from the coil, embedded in resin is connected to the
display through a connector.
 The effect of bringing the sensor in close proximity to a
ferromagnetic material causes a change in the position of the
flux lines of the permanent magnet.
Hall effect
sensor • Hall effect sensors work on the
principle that when a beam of charge
particles passes through a magnetic
field, forces act on the particles and
the current beam is deflected from its
straight line path.
• Thus one side of the disc will become
negatively charged and the other side
will be of positive charge.
• This charge separation generates a
potential difference which is the
measure of distance of magnetic field
from the disc carrying current.
Capacitive type
sensors
 Tactile sensors within this category are concerned with measuring
capacitance, which made to vary under applied load.
 The capacitance of a parallel plate capacitor depends upon the
separation of the plates and their area, so that a sensor using an
elastomeric separator between the plates provides compliance such
that the capacitance will vary according to applied load.
 Advantages:
1. Wide dynamic range
2. Linear response
3. Robust
 Disadvantages:
1. Susceptible to noise
2. Some dielectrics are temperature sensitive
3. Capacitance decreases with physical size ultimately limiting spatial
resolution.
Capacitive Tactile Element

36
 Ultrasonic
 Basic principle of operation:
Sensors
Emit a quick burst of ultrasound (50kHz), (human hearing: 20Hz to
20kHz)
 Measure the elapsed time until the receiver indicates that an echo is
detected.
 Determine how far away the nearest object is from the sensor

D =v* t
D = round-trip distance
v = speed of propagation(340 m/s)
t = elapsed time

Bat, dolphin, …
 Ultrasonic
Sensors

 Ranging is accurate but bearing has a 30 degree uncertainty.

The object can be located anywhere in the arc.
 Typical ranges are of the order of several centimeters to 30
meters.
 Another problem is the propagation time. The ultrasonic
signal will take 200 msec to travel 60 meters. ( 30 meters
roundtrip @ 340 m/s )
Ultrasonic
 Polaroid ultrasonic ranging system
Sensors
 It was developed for auto-focus of cameras.
 Range: 6 inches to 35 feet
Ultrasonic
Transducer transducer
Electronic board
Ringing:
 transmitter + receiver @ 50
KHz
 Residual vibrations or ringing
may be interpreted as the
echo signal
 Blanking signal to block any
return signals for the first
2.38ms after transmission

http://www.acroname.com/robotics/info/articles/sonar/sonar.html
Ultrasonic
 Applications:
Sensors
 Distance Measurement
 Mapping: Rotating proximity scans (maps the
proximity of objects surrounding the robot)

Doorway

Length of Echo
Robot

chair chair

Scan moving from left to right

Scanning at an angle of 15º apart can achieve best results

 Optical proximity
Sensor
 Light sensors are used in
cameras, infrared detectors,
and ambient lighting
applications

 Sensor is composed of
photoconductor such as a
photoresistor, photodiode, or
phototransistor
I
p n

+ V -
Touch
sensors
 It used to indicate that contact has been made b/w two
objects without regard to the magnitude of the
containing force.
 Simple devices are used such as limit switches, micro
switches.
 For e.g.. They can be used to indicate the presence or
absence of parts in a fixture at the pickup point along
a conveyor.
 Vision is the most powerful robot sensory
capabilities. Enables a robot to have a sophisticated sensing
mechanism that allows it to respond to its environment in
intelligent and flexible manner. Therefore machine vision is
the most complex sensor type.

Robot vision may be defined as the process of

extracting, characterizing, and interpreting information
from images of a three-dimensional world.

This process, also known as machine or

computer
vision may be subdivided into six principle areas

43
Sensing : The process that yields visual
image
Preprocessing : Deals with techniques such as noise reduction
and enhancement of details

Segmentation : The process that partitions an image into objects

of
interest

Description: Deals with that computation of features for example

size or
shape, suitable for differentiating one type of objects from another.

Recognition: The process that identifies these objects (for

example wrench, bolt, engine block, etc.)

44
 IMAGING COMPONENTS
The imaging component, the “eye” or sensor, is the first link in
the vision chain. Numerous sensors may be used to observe the
world. There are four type of vision sensors or imaging
components:

1. Point sensors

It is capable of measuring light only at a single point in

space. These sensor using coupled with a light source
(such as LED) and used as a noncontact ‘feeler’

It also may be used to create a higher – dimensions set

of vision Information by scanning across a field of view
by using mechanisms such as orthogonal set of
scanning mirrors
45
Noncontact feeler-point sensor

46
Image scanning using a point sensor
and oscillating deflecting mirrors
47
 2. Line
Sensor
Line sensors are one-
dimensional devices used to
collect vision information
from a real scene in the real
world.

 The sensor most frequently

used is a “line array” of
photodiodes or charger-
couple- device components.
 It operates in a similar Circular and cross configurations
manner to analog shift of light sensors
register, producing sequential,
synchronized output of
electrical signals,
corresponding to the light
intensity falling on an
integrated light-collecting cell.
48
3. Planar
Sensor
 A two dimensional configuration of the line-scan concept.
Two generic types of these sensors generally in use
today are scanning photomultipliers and solid-state
sensors.
 Photomultipliers are represented by television cameras, the
most common of which is the vidicon tube, which
essentially an optical-to-electrical signal converter.
 In addition to vidicon tubes, several types of solid-state
cameras are available. Many applications require the
solid- state sensors because of weight and noise factor
(solid- state arrays are less noisy but more expensive).
This is important when mounting a camera near or on
the end- effector of a robot.
49
 4. Volume
Sensor
A sensor that provide three-
dimensional information. The
sensor may obtain the
information by using the
directional laser or acoustic
range finders.

Schematic representation
of a triangulation range
finder

50
 IMAGE
REPRESENT
 From the diagram ATION
below. F(x,y) is used to denote the two-
dimensional image out of a television camera or other
imaging device.
 “x” and “y” denote the spatial coordinates (image plane)
 “f” at any point (x,y) is proportional to the brightness
(intensity)
of the image at that point.
 In form suitable for computer processing, an image function
f(x,y) must be digitized both spatially and in amplitude
(intensity). Digitization of the spatial coordinates (x,y) will be
known as image sampling, while amplitude digitization is
known as intensity or grey-level quantization.
 The array of (N, M) rows and columns, where each sample is
sampled uniformly, and also quantized in intensity is known as
a digital image. Each element in the array is called image
element, picture element (or pixel).

51
Effects of reducing
sampling grid
a) size.
512x512.
b)
256x256.
c) 128x128.
d) 64x64.
e) 32x32.

52
Effect produced by reducing the number of intensity levels while
maintaining the spatial resolution constant at 512x512. The 256-, 128- and
64-levels are of acceptable quality.
a) 256, b) 128, c) 64, d) 32, e) 16, f) 8, g) 4, and h) 2 levels
53
 ILLUMINATION
TECHNIQUES
 Illumination of a scene is an important factor that often affects
the complexity of vision algorithms.

 A well designed lighting system illuminates a scene so that

the complexity of the resulting image is minimised, while the
information required for object detection and extraction is
enhanced.

 Arbitrary lighting of the environment is often not acceptable

because it can result in low contras images, specular
reflections, shadows and extraneous details.

54
 ILLUMINATION TECHNIQUES

The angle of incidence of light on the object also influences

the result. There are several different techniques, such as
front illumination or backlighting, direct or diffuse
illumination, bright-field or dark-field illumination.

Direct front illumination (a ring light illuminates the

objects directly, more or less parallel to the optical axis of the
camera). The image appears non-uniform and mottled.
Diffuse bright-field illumination: The image appears more
uniform. There is a strong contrast between the object and
background, but the reflective surface of the connector 'floods'
the camera, i.e. the camera is "dazzled" and no longer detects
some details. Furthermore, shadows are formed over the upper
part of the connector.

Diffuse dark-field illumination: Light with an oblique angle of

incidence from a ring light with an angle between the front
illumination unit and the object. Further detail can be seen on
the connector and no shadows are formed.
Dark-field illumination:
Shallow angle of incidence of the light on the object
plane. The top edges of the pins, the connector and the
holes appear as bright circles and can thus be easily
identified busing image analysis software. The missing pin
(no bright circle) and the bent pin (incorrect position) are
more easily visible when compared to front illumination.
Backlighting:
Light is aimed towards the camera from the rear of
the object. The light only penetrates where there is nothing
to obstruct it. This allows the drill holes on each side of the
connector to be measured accurately. An easily detected
bright spot appears in place of the missing pin.
Machine vision
system
Machine
Vision
 It is the process of applying a range of technologies and
methods to provide imaging-based automatic inspection,
process control and robot guidance in industrial
applications.
 The primary uses for machine vision are automatic
inspection and robot guidance. Common MV
applications include quality assurance, sorting, material
handling, robot guidance, and optical gauging.
 creates a model of the real world from images recovers
useful information about a scene from its two
dimensional projections
Stages of machine
vision:
Image
formation
 Perspective Projection
 Orthographic projection
Image
Processing
Filtering, Smoothing, Thinning , Expending ,Shrinking
,Compressing
Image
Segmentation
 Classify pixels into groups having
similar characteristics
Image analyses
Measurements: Size, Position, Orientation,
Spatial relationship, Gray scale or color intensity
Sensing and
digitizing
 Image sensing requires some type of image formation device such as
camera and a digitizer which stores a video frame in the computer
memory.
 We divide the sensing and digitizing into several steps. The initial
step involves capturing the image of the scene with the vision
camera.
 The image consists of relative light intensities corresponding to
the various portions of the scene.
 These light intensities are continuous analog values which must be
sampled and converted into digital form.
 The second step of digitizing is achieved by an analog –to –digital
converter.
 The A/D converter is either a part of a digital video camera or the
front end of a frame grabber.
 The choice is dependent on the type of hardware system. The frame
grabber, representing the third step is an image storage and
computation device which stores a given pixel array.
Image processing and
analysis
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