INTRODUCTION TO ROBOTICS

UNIT 1
FUNDAMENTALS OF ROBOTS
Mr.R PREM KUMAR , ME
MECHANICAL ENGINEERING
KALAIGNAR KARUNANIDHI INSTITUTE OF TECHNOLOGY
COIMBATORE - 641402

2
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.

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
• Defined by Robotics 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

Accessories
• 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.

Motivation for using robots to perform task which would
otherwise be performed by humans.
• Safety
• Efficiency
• Reliability
• Worker Redeployment
• Cost reduction
The Advent of Industrial Robots

– Arm or Manipulator
– End effectors
– Drive Source
– Control Systems
– Sensors
Main Components of Industrial Robots

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

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 robotics
Uses of sensors:
– 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

WRIST
• 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

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
– Joints provide relative motion
– Links are rigid members between joints
– Various joint types: linear and rotary
– Each joint provides a “degree-of-freedom”
– Most robots possess five or six degrees-of-
freedom
• Robot manipulator consists of two sections:
– Body-and-arm – for positioning of objects
in the robot's work volume
– Wrist assembly – for orientation of objects
Base
Link0
Joint1
Link2
Link3Joint3
End of Arm
Link1
Joint2

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

Example
• Sketch following manipulator configurations
• (a) TRT:R, (b) TVR:TR, (c) RR:T.
Solution:
T
R
T
V
(a) TRT:R
R
T
R
T R
TR
R
(c) RR:T(b) TVR:TR

•Manual
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
Programming Robots

• Material Handling/Palletizing
• Machine Loading/Unloading
• Arc/Spot Welding
• Water jet/Laser cutting
• Spray Coating
• Gluing/Sealing
• Investment casting
• Processing operations
• Assembly
• Inspection
Applications

• Size of the working envelope
• Precision of movement
– Control resolution
– Accuracy
– Repeatability
•Lifting capability
•Number of robot axes
•Speed of movement
– maximum speed
– acceleration/deceleration time
•Motion control
– path control
– velocity control
•Types of drive motors
– hydraulic
– electric
– pneumatic
Performance Specifications of Industrial
Robots

Determined by
– Physical configurations
– Size
– Number of axes
– The robot mounted position (overhead gantry, wall-
mounted, floor mounted, on tracks)
– Limits of arm and joint configurations
– The addition of an end-effector can move or offset the
entire work volume
Work Volume
Spatial region within which the end
of the robot’s wrist can be
manipulated

Depends on the position control system, feedback measurement, and mechanical
accuracy
Spatial Resolution
Smallest increment of motion at the wrist end that can be controlled by the robot

• One half of the distance between two adjacent resolution
points
• Affected by mechanical Inaccuracies
• Manufacturers don’t provide the accuracy (hard to control)
Accuracy
Capability to position the wrist at a target point in the work volume

• Repeatability errors form a random variable.
• Mechanical inaccuracies in arm, wrist components
• Larger robots have less precise repeatability values
Repeatability
Ability to position back to a point that was previously taught

• 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
Weight Carrying Capacity

•Acceleration/deceleration times are crucial for cycle time.
•Determined by
– Weight of the object
– Distance moved
– Precision with which object must be positioned
Speed of Movement
Speed with which the robot can manipulate the end effector

• 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).
Motion Control

• 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
Degrees of Freedom

Robot Applications
(Configurations/Characteristics)
SCARA Robot
(Selective Compliance Assembly Robot
Arm)
Characteristics:
•Repeatability: < 0.025mm (high)
•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
Cylindrical Coordinate Robot
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
Vertical Articulated 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
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
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
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

UNIT II
ROBOT DRIVE SYSTEMS
AND END EFFECTORS
R.PREM KUMAR
AP – MECH
KIT , CBE

2004 3
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

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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 7
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

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 worm
gearing. A reduction of speed, change of
torque and angular velocity are possible.
• 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%

Actuators
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
• Stepper Motor
• Servo motor
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

Step 2
Stepper motor operation

Step 3

Step 4

• 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.
Stepper Motor

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 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.

End Effectors
Correct name for the “Hand” that is attached to the end of robot
• 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 Effector

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

Pneumatic Grippers
• Suction cups 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 Grippers
• Hooks 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.

PAINTING
DRILLING
WELDING
Tools as End Effectors

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.

• 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.

• 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.

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:
2004 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
 Inductance

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.
2004 8

Types of position sensor
 Piezoelectric sensor
 LVDT
 Resolvers
 Optical encoders
 Pneumatic position sensors

Piezoelectric sensor
 Piezoelectric sensors: a
microscopic crystal structure is
mounted 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

LVDT
 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.

 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.
LVDT

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

Resolvers
 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.
A resolver is a type of rotary electrical transformer used for measuring
degrees of rotation. It is considered an analog device, and has digital
counterparts such as the digital resolver, rotary (or pulse) encoder.

Optical encoders
It generates pulses proportional to the rotation speed of
the shaft.
grating
light emitter
light sensor
decode
circuitry
- direction
- resolution
A
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.
2004 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 pattern the
distortion of the pattern to calculate the range.
 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
2004 31

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.

Ultrasonic Sensors
 Basic principle of operation:
 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 Sensors
 Polaroid ultrasonic ranging system
 It was developed for auto-focus of cameras.
 Range: 6 inches to 35 feet
Ultrasonic
transducer
Electronic board
Transducer 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 Sensors
 Applications:
 Distance Measurement
 Mapping: Rotating proximity scans (maps the
proximity of objects surrounding the robot)
chair
Robot
chair
Doorway
Scan moving from left to right
LengthofEcho
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
p n
I
+ 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.)
Interpretation: Assigns meaning to an assembled recognized objects.
44

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
IMAGING COMPONENTS

46
Noncontact feeler-point sensor

47
Image scanning using a point sensor
and oscillating deflecting mirrors

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 manner
to analog shift register,
producing sequential,
synchronized output of
electrical signals,
corresponding to the light
intensity falling on an
integrated light-collecting cell.
48
Circular and cross configurations
of light sensors

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.
50
Schematic representation
of a triangulation range finder

IMAGE REPRESENTATION
 From the diagram 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 size.
a) 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 longerdetects 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
 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

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
Fingerprint
sensor
Fingerprint
sensor
Feature Extractor
Feature Extractor
ID
Enrollment
Identification
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database

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