ROBOTICS – SENSORS AND MACHINE VISION

WELCOME
UNIT 3 – SENSORS AND MACHINE VISION
OIE751 – ROBOTICS
(Professional elective-III)
Mr. TAMIL SELVAN M, A/P, MECH, KIT.

UNIT III – SENSOR AND MACHINE VISION
 Requirements of a sensor, Principles and Applications of the following
types of sensors- Position sensors - Piezo Electric Sensor, LVDT,
Resolvers, Optical Encoders, pneumatic Position Sensors, Range
Sensors Triangulations Principles, Structured, Lighting Approach, Time of
Flight, Range Finders, Laser Range Meters, Touch Sensors ,binary
Sensors., Analog Sensors, Wrist Sensors, Compliance Sensors, Slip
Sensors, Camera, Frame Grabber, Sensing and Digitizing Image Data-
Signal Conversion, Image Storage, Lighting Techniques, Image
Processing and Analysis-Data Reduction, Segmentation, Feature
Extraction, Object Recognition, Other Algorithms, Applications-
Inspection, Identification, Visual Serving and Navigation.

What are Sensors?
 American National Standards Institute (ANSI) Definition
“A device which provides a usable output in response to a
specified measurand”
 A sensor acquires a physical parameter and converts it into a signal
suitable for processing (e.g. optical, electrical, mechanical)
Sensor
Input Signal Output Signal

Robot Sensors
 Sensors are devices for sensing and measuring
geometric and physical properties of robots and the surrounding
environment
– Position, orientation, velocity, acceleration
– Distance, size
– Force, moment
– temperature, luminance, weight
– etc.
ultrasonic sensors
touch sensors
Infra-red sensors

Solar Cell
Digital Infrared Ranging
Compass
Touch Switch
Limit Switch
Magnetic Reed Switch
Magnetic Sensor
Pressure Switch
Miniature Polaroid Sensor
Polaroid Sensor Board
Piezo Ultrasonic Transducers
Thyristor
Gas Sensor
Gieger-Muller
Radiation Sensor
Piezo Bend Sensor
Resistive Bend Sensors
Mechanical Tilt Sensors
Pendulum Resistive
Tilt Sensors
CDS Cell
Resistive Light Sensor
Hall Effect
Magnetic Field
Sensors
Compass
IRDA Transceiver
IR Amplifier Sensor
IR Modulator
Receiver
Lite-On IR
Remote Receiver
Radio Shack
Remote Receiver
IR Sensor w/lens
Gyro
Accelerometer
IR Reflection
Sensor
IR Pin
Diode
Pyroelectric Detector
UV Detector
Metal Detector

CLASSIFICATION OF SENSORS
 Proprioceptive (“sense of self ”, internal state): Measures values
internally to the system (robot), e.g. battery level, wheel position,
joint angle, etc.
 Exteroceptive (external state): Observations of robot
environment, objects in it.
 Active: emit energy in environment more robust, less efficient.
 Passive: passively receive energy from environment less intrusive,
but depends on environment e.g. light for camera.

Internal Sensors
acceleration sensors velocity sensor
optical encoder
 Internal sensors / Proprioceptive : Obtain the information about the robot
itself. They are used to measure position, velocity and acceleration of the
robot joint or end effectors.
– position sensor, velocity sensor, acceleration sensors, motor torque sensor,
etc.

External Sensors
 External sensors / Exteroceptive : Obtain the information in the
surrounding environment.
 Cameras for viewing the environment
 Range sensors: IR sensor, laser range finder, ultrasonic sensor, etc.
 Contact and proximity sensors: Photodiode, IR detector, RFID, touch etc.
 Force sensors: measuring the interaction forces with the environment,
A mobile robot with external sensors

Basic Requirements of a Sensor
 Range: It indicates the limits of the input in which it can vary. In case of
temperature measurement, a thermocouple can have a range of 25 –
250 Centigrade.
 Accuracy: It is the degree of exactness between actual measurement
and true value. Accuracy is expressed as percentage of full range output.
 Sensitivity: Sensitivity is a relationship between input physical signal
and output electrical signal. It is the ratio of change in output of the
sensor to unit change in input value that causes change in output.
 Stability: It is the ability of the sensor to produce the same output for
constant input over a period of time.
 Repeatability: It is the ability of the sensor to produce same output for
different applications with same input value.

Cont..
 Response Time: It is the speed of change in output on a stepwise
change in input.
 Linearity: It is specified in terms of percentage of nonlinearity.
Nonlinearity is an indication of deviation of curve of actual measurement
from the curve of ideal measurement.
 Ruggedness: It is a measure of the durability when the sensor is used
under extreme operating conditions.
 Hysteresis: The hysteresis is defined as the maximum difference in
output at any measurable value within the sensor’s specified range when
approaching the point first with increasing and then with decreasing the
input parameter. Hysteresis is a characteristic that a transducer has in
being unable to repeat its functionality faithfully when used in the
opposite direction of operation.

Position sensors
 Position sensors measure the position of a joint (the degree to which the
joint is extended). They include:
 Potentiometer: a variable resistance device that expresses linear or
angular displacements in terms of voltage.
 Linear variable differential transformer: a displacement transducer that
provides high accuracy. It generates an AC signal whose magnitude is a
function of the displacement of a moving core.
 Encoder: a digital optical device that converts motion into a sequence of
digital pulses.
 Synchros and Resolvers

Linear Variable Differential Transformer (LVTD)
 The term LVDT or Linear Variable Differential Transformer is a robust, complete
linear arrangement transducer and naturally frictionless. They have an endless
life cycle when it is used properly. Because AC controlled LVDT does not
include any kind of electronics, they intended to work at very low temperatures
otherwise up to 650 °C (1200 °F) in insensitive environments.
 The applications of LVDTs mainly include automation, power turbines, aircraft,
hydraulics, nuclear reactors, satellites, and many more. These types of
transducers contain low physical phenomena and outstanding repetition.
 The LVDT alters a linear dislocation from a mechanical position into a relative
electrical signal including phase and amplitude of the information of direction
and distance. The operation of LVDT does not need an electrical bond between
the touching parts and coil, but as an alternative depends on the
electromagnetic coupling.

Cont…
 The core is protected by the thing whose
location is being calculated, while the coil
assembly is increased to a stationary
structure. The coil assembly includes three
wire wound coils on the hollow shape. The
inside coil is the major, which is
energized by an AC source. The magnetic
flux generated by the main is attached to
the two minor coils, making an AC
voltage in every coil.
 LVDT is a normal type of transducer. The
main function of this is to convert the
rectangular movement of an object to the
equivalent electrical signal. LVDT is used to
calculate displacement and works on the
transformer principle.
Linear Variable Differential Transformer
(LVTD)

LVDT Construction
 LVDT comprises of a cylindrical former, which is bounded by one main winding in
the hub of the former and the two minor LVDT windings are wound on the
surfaces. The amount of twists in both the minor windings is equivalent, but they
are reverse to each other like clockwise direction and anti-clockwise direction.
 For this reason, the o/p voltages will be the variation in voltages among the two
minor coils. These two coils are denoted with S1 & S2. Esteem iron core is
located in the middle of the cylindrical former. The excitation voltage of AC is 5-
12V and the operating frequency is given by 50 to 400 HZ.
LVDT Construction

Working Principle of LVDT
 The working principle of the linear variable differential transformer or LVDT
working theory is mutual induction. The dislocation is a nonelectrical energy
that is changed into an electrical energy. And, how the energy is altered is
discussed in detail in the working of an LVDT.

Working of an LVDT
 The working of LVDT circuit diagram can be divided into three cases based
on the position of the iron core in the insulated former.
 In Case-1: When the core of the LVDT is at the null location, then both the
minor windings flux will equal, so the induced e.m.f is similar in the
windings. So for no dislocation, the output value (eout) is zero because both
the e1 & e2 are equivalent. Thus, it illustrates that no dislocation took place.
 In Case-2: When the core of the LVDT is shifted to up to the null point. In
this case, the flux involving with minor winding S1 is additional as
contrasted to flux connecting with the S 2 winding. Due to this reason, e1
will be added as that of e2. Due to this eout (output voltage) is positive.
 In Case-3: When the core of the LVDT is shifted down to the null point, In
this case, the amount of e2 will be added as that of e1. Due to this
eout output voltage will be negative plus it illustrates the o/p to down on the
location point.

Advantages and Disadvantages of LVDT
 The measurement of the displacement range of LVDT is very high, and it ranges from
1.25 mm -250 mm.
 The LVDT output is very high, and it doesn’t require any extension. It owns a high
compassion which is normally about 40V/mm.
 When the core travels within a hollow former consequently there is no failure of
displacement input while frictional loss so it makes an LVDT as a very precise device.
 LVDT demonstrates a small hysteresis and thus repetition is exceptional in all situations
 The power consumption of the LVDT is very low which is about 1W as evaluated by
another type of transducers.
 LVDT changes the linear dislocation into an electrical voltage which is simple to progress.
 LVDT is responsive to move away from magnetic fields, thus it constantly needs a system
to keep them from drift magnetic fields.
 It is accomplished that LVDTs are more beneficial as contrasted than any kind of
inductive transducer.
 LVDT gets damaged by temperature as well as vibrations.

LVDT Applications
The applications of the LVDT transducer mainly include where
dislocations to be calculated that are ranging from a division of mm to only
some cms.
 The LVDT sensor works as the main transducer, and that changes
dislocation to electrical signal straight.
 This transducer can also work as a secondary transducer.
 LVDT is used to measure the weight, force and also pressure
 Some of these transducers are used to calculate the pressure and load
 LVDT’s are mostly used in industries as well as servomechanisms.
 Other applications like power turbines, hydraulics, automation, aircraft, and
satellites

RESOLVER
 A rotating electrical transformer that is used to measure degrees of
rotation is known as a resolver.
 It includes digital counterparts like the rotary encoder and the digital
resolver.
 It is used in different velocity and position feedback applications
because of their good performance like servo motor feedback, light-duty,
heavy-duty and light industrial.
 These are also called as a motor resolver.
RESOLVER

Cont..
It is an analog device & the electrical outputs of this device
are continuous during one whole mechanical rotation.
It is a rugged device compared with other feedback devices
due to its simple transformer design.
It is applicable where the consistent performance is
necessary for those vibration, radiation, high shock, high
temperature as well as contagion environments.
Generally, the selection of this mainly determined by the
size of the shaft, transformation ration, and excitation
frequency.

CONSTRUCTION OF RESOLVER
 It is a special kind of rotating transformer,
includes a stator and rotor in a cylindrical
shape.
 These are designed with two sets of windings
and multi-slot laminations.
 Usually, these windings are designed as well
as distributed within the slotted lamination
through a stable pitch-variable twist otherwise
changeable pitch-variable twist model.
 For a single speed type, the windings will
create one whole Sine curve & Cosine curve
in one rotation whereas, for a multi-speed
type, the windings will create various Sine
curves & Cosine curves within one rotation.

Cont..
 Whenever a single-speed gives
complete feedback but multi-speed
doesn’t give.
 The number of speeds obtainable is
imperfect with the resolver size.
 The set of windings is located within
the laminations with 90o to each
other, known as Sine & Cosine
windings.
 Here, the accuracy can be
enhanced once the set of windings
within the rotor is shorted internally.

WORKING PRINCIPLE OF RESOLVER
 The resolver works on the principle of
an electrical transformer.
 These transformers use copper
windings in stator and rotor.
 Based on the rotor’s angular position,
the inductive coupling of the windings
will be changed.
 The resolver energizes by using an
AC signal and the output of this can
be measured to provide an electrical
signal.

Cont..
 Generally, it includes three windings like
one primary and two secondaries. These
are designed with the help of copper wire
on the stator. The primary winding
functions like the i/p for an AC signal
whereas each of the secondary winding is
used as output. In this, the stationary part
is designed with iron or steel.
 The operation of this can be done by
different operating parameters like
accuracy, i/p excitation voltage, excitation
frequency, maximum current,
transformation ration, phase shift, and null
voltage.

Advantages & Disadvantages
The advantages of resolver include the following.
 Accurate
 Reliable
 Tolerant to Misalignment
 Robust
 Durability
The disadvantages of resolver include the following.
 Expensive
 Heavy
 Requires skillful specification & implementation
 Bulky


APPLICATION
Resolvers are used in the feedback of the servo motor
Surface actuators
Used in paper and steel mills for speed & position feedback
Control systems of military vehicles
Communication position systems
Fuel systems of the Jet engine
Production of gas and oil
It is used in vector resolution to split the vector into different
parts
Vector angle & component can be determined
The amplitude of pluses and pulse resolution can be controlled

OPTICAL ENCODERS
 The encoder is a sensor attached to a rotating object (such as a wheel or
motor) to measure rotation.
 By measuring rotation your robot can do things such as determine
displacement, velocity, acceleration, or the angle of a rotating sensor.

OPTICAL ENCODERS
• Any transducer that generates a coded reading of a
measurement can be termed an encoder.
• Shaft Encoders are digital transducers that are used for
measuring angular displacements and velocities.
• Relative advantages of digital transducers over their
analog counterparts:
–High resolution (depending on the word size of the
encoder output and the number of pulses per revolution
of the encoder)
–High accuracy (particularly due to noise immunity of
digital signals and superior construction)

– Relative ease of adaptation in digital control systems
(because transducer output is digital) with associated
reduction in system cost and improvement of system reliability
• Shaft Encoders can be classified into two categories
depending on the nature and method of interpretation of the
output:
– Incremental Encoders
– Absolute Encoders
• Incremental Encoders
– Output is a pulse signal that is generated when the
transducer disk rotates as a result of the motion that is
being measured.

– By counting pulses or by timing the pulse width using a clock signal,
both angular displacement and angular velocity can be determined.
– Displacement, however, is obtained with respect to some
reference point on the disk, as indicated by a reference pulse
(index pulse) generated at that location on the disk. The index
pulse count determines the number of full revolutions.
• Absolute Encoders
– An absolute encoder has many pulse tracks on its
transducer disk.
– When the disk of an absolute encoder rotates, several pulse
trains equal in number to the tracks on the disk are generated
simultaneously.

– At a given instant, the magnitude of each pulse signal will have one of
two signal levels (i.e., a binary state) as determined by a level detector.
– This signal level corresponds to a binary digit (0 or 1). Hence, the set
of pulse trains gives an encoded binary number at any instant.
– The pulse windows on the tracks can be organized into some pattern
(code) so that each of these binary numbers corresponds to the angular
position of the encoder disk at the time when the particular binary
number is detected.
– Pulse voltage can be made compatible with some form of digital logic
(e.g., TTL)
– Direct digital readout of an angular position is possible.

– Absolute encoders are commonly used to measure fractions of a
revolution. However, complete revolutions can be measured using
an additional track that generates an index pulse, as in the case of
an incremental encoder.
• Signal Generation can be accomplished using any one of four
techniques:
– Optical (photosensor) method
– Sliding contact (electrical conducting) method
– Magnetic saturation (reluctance) method
– Proximity sensor method
• Method of signal interpretation and processing is the same for
all four types of signal generation.

(slits)
Schematic Representation of an Optical Encoder One Track and One
Pick-Off Sensor Shown

In Binary Code, bit switching may
not take place simultaneously.
Schematic Diagram of an
Absolute Encoder Disk
Pattern
(a)Binary code
(b)Gray code
Ambiguities in bit switching can be
avoided by using gray code.
However, additional logic is needed
to covert the gray-coded number to a
corresponding binary number.
Absolute Encoders must
be powered and
monitored only when a
reading is taken. Also, if a
reading is missed, it will
not affect the next reading.

(Electrically Insulating Material)
Schematic Representation of a Sliding Contact Encoder

Pulse peak: nonmagnetic are
Pulse valley: magnetic area
Schematic Representation of a Magnetic Encoder

Proximity sensor:
Magnetic induction
ferromagnetic
material
Schematic Representation of a Proximity Probe Encoder

• ELEMENTS OF THE OPTICAL ENCODER
– The optical encoder uses an opaque disk (code disk) that
has one or more circular tracks, with some arrangement of
identical transparent windows (slits) in each track.
– A parallel beam of light (e.g., from a set of light- emitting
diodes) is projected to all tracks from one side of the disk.
– The transmitted light is picked off using a bank of
photosensors on the other side of the disk that typically has
one sensor for each track.
– The light sensor could be a silicon photodiode, a
phototransistor, or a photovoltaic cell.

Incremental Optical Encoder Disk Offset-Sensor
Configuration

Incremental Encoder Pulse Signals
(a) CW rotation (b) CCW rotation (c) reference
Clockwise (CW) rotation:
V1 lags V2 by a quarter of a cycle (i.e.,
a phase lag of 90 ) Counterclockwise
(CCW) rotation: V1 leads V2 by a
quarter of a cycle

Piezoelectric sensor
 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.
 Where piezoelectricity is a phenomenon where electricity is
generated if mechanical stress is applied to a material. Not all
materials have piezoelectric characteristics.
 The prefix piezo- is Greek for 'press' or 'squeeze’.
 There are various types of piezoelectric materials. Examples of
piezoelectric materials are natural available single crystal quartz,
bone etc… Artificially manufactured like PZT ceramic etc…

Principle of operation
The way a piezoelectric material is cut defines one of its three
main operational modes:
 Transverse
 Longitudinal
 Shear.
Piezoelectric sensor

Working of a Piezoelectric Sensor
 The commonly measured physical quantities by a piezoelectric sensor are
Acceleration and Pressure. Both pressure and acceleration sensors work on
the same principle of piezoelectricity but the main difference between them
is the way force is applied to their sensing element.
 In the pressure sensor, a thin membrane is placed on a massive base to
transfer the applied force to the piezoelectric element. Upon application of
pressure on this thin membrane, the piezoelectric material gets loaded and
starts generating electrical voltages. The produced voltage is proportional to
the amount of pressure applied.
 In accelerometers, seismic mass is attached to the crystal element to
transfer the applied force to piezoelectric materials. When motion is applied,
seismic mass load’s the piezoelectric material according to Newton’s
second law of motion. The piezoelectric material generates charge used for
calibration of motion.

Piezoelectric Sensor Circuit
 The resistance Ri is the internal resistance or insulator resistance. The
inductance is due to the inertia of the sensor. The capacitance Ce is
inversely proportional to the elasticity of the sensor material. For the
proper response of the sensor, the load and leakage resistance must be
large enough so that low frequencies are preserved. A sensor can be
called a pressure transducer in an electrical signal. Sensors are also
known as primary transducers.
A piezoelectric sensor internal circuit

Piezoelectric Sensor Specifications
 Some of the basic characteristics of piezoelectric sensors are
 The range of measurement: This range is subject to measurement limits.
 Sensitivity S: Ratio of change in output signal ∆y to the signal that caused the change ∆x.
S = ∆y/∆x.
 Reliability: This accounts to the sensors ability to keep characteristics in certain limits
under set operational conditions.
 Besides these, some of the specifications of piezoelectric sensors are a threshold of reaction,
errors, time of indication etc…
 These sensors contain as Impedance value ≤500Ω.
 These sensors generally operate in a temperature range of approximately -20°C to +60°C.
 These sensors are to be kept at a temperature between -30°C to +70°C to prevent them from
degradation.
 These sensors have very low Soldering temperature.
 Strain sensitivity of a piezoelectric sensor is 5V/µƐ.
 Due to its high flexibility Quartz is the most preferred material as a piezoelectric sensor.

Piezoelectric Sensor Applications
Piezoelectric sensors are used for shock detection.
Active piezoelectric sensors are used for thickness gauge, flow sensor.
Passive piezoelectric sensors are used microphones, accelerometer,
musical pickups etc…
Piezoelectric sensors are also used for ultrasound imaging.
These sensors are used for optic measurements, micro moving
measurements, electro acoustics etc…

PNEUMATIC POSITION SENSORS
 Sensors are used to provide position feedback to control systems in
automated machinery and equipment.
 Pneumatic cylinders use sensors to detect the linear position of the
piston for applications where position feedback is crucial.
 The most common type of sensor used for pneumatic cylinders are
magnetic proximity sensors, which detect the magnetic field of a magnet
integrated in the cylinder piston.

PNEUMATIC SENSORS: THEIR USE AND PERFORMANCE IN
FORCE, TACTILE AND POSITION SENSING AND IN SHAPE
RECOGNITION
 The application of pneumatic sensors on robots or manipulation systems is
possibile and convenient in some cases when the use of compressed air is
particularly suitable.
 Pneumatic sensors may be air jet, contactless devices, or otherwise contact
sensors.
 Air jets may be arranged to work as proximity sensors, while pneumatic
contact devices may be used as touch sensors or may be arranged to
measure pressure or force.
 Proximity sensors are used on the tip of grasping fingers for providing hand
closure signals, or for measuring the distance between workpiece and
fingers.

Cont..
 The workpiece re-orientation devices, that often supply a robot, may also
be provided with proximity sensors for defining workpiece position.
Proximity sensors may be requested to give out a threshold signal; for
example, they must provide a digital signal when the measured distance is
less then a given value; in other cases, they must give out a proportional
signal.
 The same sensor may often perform both functions; the threshold is
established by pneumatically elaborating the output signal. Some sensors
are intrinsically digital, as the sensors based on jet obstruction by an
interposed solid object.
 A jet interruption sensor is made by an emitting nozzle and a receiving
tube, where it is measured the recovery pressure, that is the stagnation
pressure of the recovered part of the jet.

Structured Lighting Approach:
 This approach consists of projecting a light pattern the distortion of
the pattern to calculate the range. A pattern in use today is a sheet of
light generated narrow slit.
 As 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.
 Specific range values are computed by first calibrating the system.

Cont..
 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.
 We call the vertical plane containing this line the reference plane.
 Clearly, the reference plane is perpendicular to the sheet of light, and any
vertical flat surface that intersects the sheet will produce a vertical stripe of
light in which every point will have the same perpendicular distance to the
reference plane.
 The objective of the arrangement to position the camera so that every
such vertical stripe also appears vertical in the image plane.
 In this way, every point, the same column in the image will be known to
have the same distance to the reference plane.

TOUCH SENSOR
 Touch Sensors are the electronic sensors that can detect touch.
 They operate as a switch when touched.
 These sensors are used in lamps, touch screens of the mobile, etc…
 Touch sensors offer an intuitive user interface.
 Touch sensors are also known as Tactile sensors
 Tactile sensors are used in robotics, computer hardware and security
systems.
 A common application of tactile sensors is in touchscreen devices on mobile
phones and computing.
 Tactile sensors may be of different types including piezoresistive,
piezoelectric, capacitive and elastoresistive sensors.

WORKING PRINCIPLE OF TOUCH SENSOR
 Touch sensors work similar to a switch.
When they are subjected to touch, pressure
or force they get activated and acts as a
closed switch. When the pressure or contact
is removed they act as an open switch.
 Capacitive touch sensor contains two
parallel conductors with an insulator
between them. These conductors plates act
as a capacitor with a capacitance value C0.
 A capacitance measuring circuit
continuously measures the capacitance C0
of the sensor. When this circuit detects a
change in capacitance it generates a signal.

Cont..
 The resistive touch sensors calculate the pressure applied on the
surface to sense the touch. These sensors contain two conductive films
coated with indium tin oxide, which is a good conductor of electricity,
separated by a very small distance.
 Across the surface of the films, a constant voltage is applied. When
pressure is applied to the top film, it touches the bottom film. This
generates a voltage drop which is detected by a controller circuit and
signal is generated thereby detecting the touch.

APPLICATION
 Capacitor sensors are easily available and are of very low cost. These
sensors are highly used in mobile phones, iPods, automotive, small home
appliances, etc… These are also used for measuring pressure, distance,
etc… A drawback of these sensors is that they can give a false alarm.
 Resistive touch sensors only work when sufficient pressure is applied.
Hence, these sensors are not useful for detecting small contact or
pressure. These are used in applications such as musical
instruments, keypads, touch-pads, etc.. where a large amount of pressure
is applied.
 Examples
 Some of the examples of touch sensors available in the market are
TTP22301, TTP229, etc…

BINARY SENSOR
 Binary sensors gather information about the state of devices which
have a “digital” return value (either 1 or 0). These can be switches,
contacts, pins, etc. These sensors only have two
states: 0/off/low/closed/false and 1/on/high/open/true.
presence: on means home, off means away

WORKING PRINCIPLE OF BINARY SENSOR
 Binary sensors operate based on the principle that the distribution of
touch and no-touch values across the sensor array would provide a
measure of the spatial distribution of force. These sensors are contact
switches that are placed on the inner side of each finger of a robotic
hand. This type of sensing can sense an object by moving the hand over
the object and making contact with its surface.
 Each finger can be designed with multiple switches to provide more
tactile information. These switches are mostly mounted on the external
surfaces of the hand to produce a control signal for directing the hand
over the workspace. Meanwhile, the proper manipulation and grasping of
the object in the workspace can be achieved via centering of the fingers
using the information given by the binary sensors.

Cont..
 The binary sensor detects whether the robot or object has crossed it,
and it maintains a sensing abstraction that includes various physical
sensing modalities such as swap lines that indicates the change of
angular position of the workspace, linear markings in the plane, and
other actual detection beams in the surrounding. All such information will
be utilized in identifying the presence of objects.

Applications
 Binary sensors could also be utilized in various applications, including
transportation, communication, or chemical engineering. For example,
radio frequency identification (RFID) readers can detect the presence of
RFID tags. These tags are usually used as wireless tracking devices or
access control in transportation.
 Meanwhile, binary chemical sensors could detect the presence of
chemical compounds, toxic plumes or oil spills in the fields and seas.

ANALOGUE SENSOR
 Analogue Sensors produce a
continuous output signal or voltage
which is generally proportional to
the quantity being measured.
Physical quantities such as
Temperature, Speed, Pressure,
Displacement, Strain etc are
all analogue quantities as they tend
to be continuous in nature.

WORKING PRINCIPLE OF ANALOGUE SENSOR
 Analog Sensors output a change in
electrical property to signify a
change in its environment. The
change can be a variation in
Voltage, Current, Resistance,
Charge and Capacitance. Sensor
circuits are designed to monitor
these changes and provide a
voltage difference.
 This voltage difference, if required
can be converted into a digital value
and processed further.

Cont..
 All modern microcontrollers have Analog to Digital converter circuitry
built-in. For example, if we consider a Photoresistor, the resistance in a
Photoresistor changes with the amount of light falling on it. The
Photoresistor circuitry creates a voltage difference based on the change
in resistance and an analog signal is fed into the microcontroller. This
analog signal, if required can be further converted into a digital value and
processed as per the requirement (For further information, suggest you
to read Analog to digital Conversion). Since most microcontrollers work
within the 0V to +5V range, the sensor circuitry is designed such that it
generates a continuous signal between 0 Volts to +5 Volts as an output.

WRIST SENSORS
 Several different forces exist at the point where a robot arm joins the end
effector. This point is called the wrist. It has one or more joints that move in
various ways. A wrist-force sensor can detect and measure these forces. It
consists of specialized pressure sensors known as strain gauges. The
strain gauges convert the wrist forces into electric signals, which go to the
robot controller. Thus the machine can determine what is happening at the
wrist, and act accordingly.
 Wrist force is complex. Several dimensions are required to represent all the
possible motions that can take place. The illustration shows a hypothetical
robot wrist, and the forces that can occur there. The orientations are
right/left, in/out, and up/down. Rotation is possible along all three axes.
These forces are called pitch, roll, and yaw. A wrist-force sensor must detect,
and translate, each of the forces independently. A change in one vector must
cause a change in sensor output for that force, and no others.

SLIP SENSOR
 Humans can grasp an object
without information such as a
coefficient of friction or weight.
 To implement this grasping motion
with the robot hand, sensors have
been proposed that detect an
incipient slip within the contact
surface or stick-slip.

WORKING PRINCIPLE OF SLIP SENSOR
 The voltage difference Vp is measured and the signal processing is
performed. Then the initial slip can be detected. The pressure conductive
rubber was a high polymer material primarily composed of silicone rubber
with carbon particles uniformly distributed within.
 In an unloaded condition, the electrical resistance is infinity. However, the
electrical resistance changes when the normal force was added, because
the mutual contact between carbon particles increases. Moreover, when
added a tangential force, the electrical resistance randomly changes by
changing the mutual contact between carbon particles.

Cont..
 As shown in figure, the object is placed on
the surface of the sensor. The upper graph
shows the output of the slip sensor when
pulling force is applied to the object.
The lowest graph shows the pulling force and
its position shifts through slippinge.
First, the pulling force is increased until about
0.15s, after which it remains roughly
constant. Specifically, it can be considered
that a transition from static friction to dynamic
friction occurs at the place marked with a
verticalline in the figure. At which point, a slip
occurs between the object and the surface of
the sensor. This is also clearly seen with the
measurement of a laser displacement sensor.

Cont..
 Here, looking at the enlarged portion of the upper graph, a complex change
in the voltage emerges immediately before the occurrence of slip (the time
of the initial slip).
 Upon performing a frequency analysis with respect to this voltage change,
it was found that the sensor output Vp at the time of the initial slip includes
a high frequency component of several kHz to several 10kHz.
 In this regard, such high-frequency change does not occur when the
change in force is in normal direction.
 The slip sensor presented here extracts this high-frequency component by
applying the discrete wavelet transform (DWT) and detects the initial slip of
the object.
 The middle graph presents the results of DWT power using Haar wavelets.
It is clear that immediately before slip occurs, the DWT power increases.

Machine vision is the technology to replace or complement manual
inspections and measurements with digital cameras and image processing.
The technology is used in a variety of different industries to automate the
production, increase production speed and yield, and to improve product
quality. Machine vision in operation can be described by a four-step flow:
1.Imaging : Take an image.
2.Processing and analysis : Analyze the image
to obtain a result.
3.Communication: Send the result to the system
in control of the process.
4.Action: Take action depending on the vision
system's result.
INTRODUCTION

COMPONENTS OF MACHINE VISION SYSTEM

LIGHTING SYSTEM
 Lighting system refers to lighting sources and lighting types available
around the object being analysed.
 It is significant that the object(s) under analysis be clearly visible to the
image acquisition device.
 It ensures that much of the information is retained in the acquired
image, and no much image processing needs to be done; thus making
the machine vision application simpler to develop.

LIGHTING SOURCES
 Common light sources are as follows,
 Fluorescent tubes
 Halogen and xenon lamps
 LED
 Laser
 LED lights are more preferred over the other types of light
sources, because of their long life and less energy
consumption

LIGHTING TYPES
 There is a large variety of different lighting types that are
available for machine vision.
 The types listed here represent some of the most commonly
used techniques.

LASER LIGHTING
 A laser is a device that emits light through a process of optical
amplification based on the stimulated emission of electromagnetic
radiation.
 Lasers can also have high temporal coherence, which allows them to
emit light with a very narrow spectrum, i.e., they can emit a single color
of light.
RING LIGHTING
 A ring light is a circular lighting tool that evenly illuminates the subject of a
close-up photograph.
 Ring lights are popular in portrait photography.
 The ring lights main purpose is to cast an even light onto the subject.
This reduces shadows in the face and minimizes blemishes.

SPOTLIGHT (THEATRE LIGHTING)
 A spotlight (or followspot) is a powerful stage lighting instrument which
projects a bright beam of light onto a performance space.
 Spotlights are controlled by a spotlight operator who tracks actors around
the stage.
BACK LIGHT
 Back lighting projects even illumination from behind the target highlighting
the silhouette of the target.
 This lighting type is used to detect the presence/absence of holes or gaps,
measurement or verification of the target outline shape, as well as
enhancing cracks, bubbles, and scratches on clear target parts.

ON-AXIS VISION LIGHTING
 On-axis vision lighting provides even, diffused illumination for flat,
reflective surfaces.
 A beam splitter directs the light rays along the same axis as the camera
lens.
 Reflective surfaces perpendicular to the camera appear bright.
Surfaces at an angle to the camera and non-reflective surfaces appear
dark.
DARK FIELD LIGHTING
 Dark field lighting involves orienting lights between 0 and 45 degrees
off horizontal,
 which is particularly effective when imaging highly reflective surfaces or
generating edge effects.

DOME LIGHTING
 Dome lighting provides uniform light from various angles which
results in no glare, even on mirrored objects.
 It's often referred to as "cloudy day" illumination since it removes
uneven lighting (glare/shadows) and evenly spreads the lighting
across the surface of the part.
 Dome illumination is used most often to inspect shiny, curved, or
bumpy surfaces.
 To be effective, dome lights require close proximity to the target.

CAMERA
Cameras used for machine vision are categorized into vision
sensors, smart cameras, and PC-based systems. All camera types are
digital, as opposed to analog cameras in traditional photography.
1. Vision Sensors : A vision sensor is a specialized vision
system that is configured to perform a specific task, unlike
general camera systems that have more flexible
configuration software. It is used for color sorting,
contour verification, and text reading functionality.

2. Smart Cameras : A smart camera is a camera with a built-in image analysis
unit that allows the camera to operate stand alone without a PC.
2D Smart : The IVC-2D (Industrial Vision Camera) is a stand- alone vision
system for 2D analysis
Measurement of ceramic part dimensions.

Misaligned label on the cap.
3D Smart
The IVC-3D is a stand-alone vision system for 3D analysis. It scans calibrated 3D
data in mm, analyzes the image, and outputs the result.

Scanned wood surface with defects.
3. PC-based Systems : In a PC-based system the camera captures the image
and transfers it to the PC for processing and analysis.
The Ruler collects calibrated 3Dshape data in
mm and sends the image to a PC for
analysis.

Volume measurement and presence detection of apples in a
box.
Multi-Scan Camera
The Ranger C55 (MultiScan) scans three different kinds of
images. They are,
1.Gray scale for print verification
2.Gloss for crack detection
3.3D for shape verification.

FRAME GRABBER
A device that captures a single frame from an analog video signal
(from a video camera or VCR) and stores it as a digital image under
computer control.

GAIN AMPLIFIER
 Gain is basically a measure of how much an amplifier “amplifies” the
input signal.
 For example, if we have an input signal of 1 volt and an output of 50
volts, then the gain of the amplifier would be “50”.
 Amplifier gain is simply the ratio of the output divided-by the input.
SYNCHRONIZATION CIRCUIT
 In digital electronics, synchronous circuit is a digital circuit in which
the changes in the state of memory elements are synchronized by a
clock signal.
 In a sequential digital logic circuit, data is stored in memory devices
called flip-flops or latches.

ANALOG TO DIGITAL CONVERTER
 Analog to Digital converter is an electronic device which converts analog
signal from our real world into a machine readable or binary or digital
format.
 For this all you need is a component which can convert physical real
world analog signals into voltage signals.
PHASE CORRECTION
 Phase correction is the process of mixing the real and imaginary
signals in the complex spectrum that is obtained after Fourier
transformation of the free induction decay.

ACQUISITION CLOCK
 Acquisition Time is the time that it takes for the ADC to acquire and
convert an analog signal to a digital value.
 The conversion time is a sum of: (Sample Time) + (Calibration Time) +
(Charge Distribution Time) + (Synchronization Time)
MEMORY BUFFER
 A memory buffer register is the register in a computer's processor, or
central processing unit, CPU, that stores the data being transferred to
and from the immediate access storage.
 It contains the copy of designated memory locations specified by the
memory address register.

PCI BUS
 Peripheral Component Interconnect is a local computer bus for
attaching hardware devices in a computer and is part of the PCI
Local Bus standard.
 The PCI bus supports the functions found on a processor bus but in
a standardized format that is independent of any particular
processor's native bus.

 A camera is used in the sensing and digitizing tasks for viewing the images.
 It will make use of special lighting methods for gaining better picture contrast.
These images are changed into the digital form, and it is known as the frame of
the vision data.
 A frame grabber is incorporated for taking digitized image continuously at 30
frames per second. Instead of scene projections, every frame is divided as a
matrix.
 By performing sampling operation on the image, the number of pixels can be
identified.
 The pixels are generally described by the elements of the matrix. A pixel is
decreased to a value for measuring the intensity of light.
 As a result of this process, the intensity of every pixel is changed into the digital
value and stored in the com memory.
SENSING & DIGITIZING IMAGE DATA

INSPECTION
 Robotic-based vision inspection deploys one or more robots with
cameras and lighting mounted on the end effectors , which automatically
move to key inspection points of a subassembly to check specific
features.
 The camera contains a sensor that converts light from the lens into
electrical signals.
 These signals are digitized into an array of values called pixels and
processed by a Vision Appliance to perform the inspection.
 After the inspection points have been selected, vision software can then
be programmed to inspect the locations on any subsequent product
presented to it.

IDENTIFICATION
 Using inspection and identification, a robot with machine
vision can select required parts by classifying them through their
unique visual features.
 This allows production equipment to be able to automatically locate
and identify items, speeding up production processes and
reducing the required manpower.

VISUAL SERVING
 Robot vision refers to the capability of a robot to visually perceive
the environment and use this information for execution of various
tasks.
 Visual feedback has been used extensively for robot navigation
and obstacle avoidance.

NAVIGATION
 Robot navigation means the robot's ability to determine its own
position in its frame of reference and then to plan a path towards some
goal location.
Which technology is used in robot navigation?
 LIDAR. In local navigation techniques, sensors are usually employed
to control the orientation and position of robot.
 For such use, LIDAR sensor is frequently used for automation purpose.
LIDAR works independently as compared to GPS system; therefore, it
has the capability of mapping the environment.

APPLICATION OF MACHINE VISION
 Final inspection of sub-assemblies
 Engine part inspection
 Label inspection on products
 Checking medical devices for defects
 Final inspection cells
 Robot guidance
 Verifying data matrix codes
 Checking orientation of components
 Traceability of manufactured
products
 Packaging Inspection
 Checking laser marks and cuts
 Medical vial inspection
 Food pack checks
 Reading bar codes
 Verifying engineered component

NPTEL VIDEO FOR MACHINE VISION
 https://youtu.be/rYaTu3Y2DMY
 https://youtu.be/HITCMaNCFQ8
 https://youtu.be/HQgU76ZOP0o

ROBOTICS – SENSORS AND MACHINE VISION

More Related Content

What's hot (20)

Similar to ROBOTICS – SENSORS AND MACHINE VISION (20)

Recently uploaded (20)

ROBOTICS – SENSORS AND MACHINE VISION