2. Assignment 2
1.Differentiate between the following types of
sensors.
(a) Proximity sensors
(b) Tactile sensors
2.Identify and explain FIVE desirable features of
robotic sensors.
3.With the aid of a diagram explain how ultrasonic
sensor works and how the distances are
computed.
3. ROBOTIC SENSORS
❖ Sensors are devices that can sense and measure physical
properties of the environment, e.g. temperature, luminance,
resistance to touch, weight, size, etc.
❖ Transduction (engineering) is a process that converts one type
of energy to another.
❖ They deliver low-level information about the environment.
4. Transducers and sensors
❖Transducer is a device that converts one type of physical
variable (eg; force, temperature, velocity, flow rate etc) into
another form.
❖It is generally converted to electrical voltages. (Reason: the
converted signal is more convenient to use and evaluate)
❖Sensor is just used to sense the signals.
❖Any transducer or sensor requires calibration in order to be
useful as a measuring device.
❖Calibration is the procedure by which the relation between the
measured variable and the converted output signal is
established
5. Types of transducers
❖Analog Trancducers: Provides a continuous signal such as
electrical voltage or current as output .
❖Digital Trancducers: Provides digital output signal in the
form of status bits or series of pulses that can be counted.
Output value represents the measured value.Digital
trancducers are more easy to read the output and they offer
high accuracy and more compatible with digital computer than
analog based sensors.
6. Desirable features of Sensors
1. Accuracy : Accuracy should be high. How close output to the true value is the
accuracy of the device.
2. Precision : There should not be any variations in the sensed output over a period of
time. Precision of the sensor should be high.
3. Operating Range : Sensor should have wide range of operation and should be
accurate and precise over this entire range.
4. Speed of Response : Should be capable of responding to the changes in the sensed
variable in minimum time.
5. Calibration : Sensor should be easy to calibrate time and trouble required to calibrate
should be minimum. It should not require frequent recalibration.
6. Reliability : It should have high reliability. Frequent failure should not happen.
7. Cost and Ease of operation :Cost should be as low as possible, installation, operation
and maintenance should be easy and should not required skilled or highly trained
persons.
9. General categories of sensors
❖Generally two categories of sensors used in
robotics;
❑ Internal and
❑ External sensors
10. General categories of sensors(cont)
❖Internal sensors:
❑Used for internal purposes.
❑Used to monitor and control the various joints of the robot; they form a
feedback control loop with the robot controller.
❑Examples of internal sensors include potentiometers and optical
encoders, tachometers of various types can be deployed to control the
speed of the robot arm.
❖External sensors:
❑Used for external purposes.
❑They are external to the robot itself, and are used when we wish to
control the operations of the robot with other pieces of equipment in the
robotic work cell.
❑External sensors can be relatively simple devices, such as limit switches
that determine whether a part has been positioned properly, or whether a
part is ready to be picked up from an unloading bay.
11. Advanced sensor technologies forrobotics
Sensor Type Description
Tactile sensors
Used to determine whether contact is made between sensor
and another object. Two types: touch sensors—which indicate
when contact is made, or not; and force sensors—which
indicate the magnitude of the force with the object.
Proximity sensors
Used to determine how close an object is to the sensor. Also
called a range sensor.
Optical sensors
Photocells and other photometric devices that are used to
detect the presence or absence of objects. Often used in
conjunction to proximity sensors.
Machine vision
Used in robotics for inspection, parts identification, guidance,
and other uses.
Others
Miscellaneous category of sensors may also be used; including
devices for measuring: temperature, fluid pressure, fluidflow,
electrical voltage, current, and other physical properties.
13. Proximity Sensor (Range sensor):
❖Ranging sensors include sensors that require no physical contact with the
object being detected.
❖They allow a robot to see an obstacle without actually having to come into
contact with it.
❖Useful for better obstacle avoidance
❖Light-based ranging sensors use multiple methods for detecting
obstacles and determining range.
❖Example 1 -- the intensity of the reflected light from an obstacle to
estimate distance. Note: this can be significantly affected by the
color/reflectivity of the obstacle and external light sources.
❖Example 2 -- Use of a beam of light projected at an angle and a strip of
detectors spaced away from the emitter as in the animation to the right.
❖Note: This method is less affected by the color/reflectivity of the object
and ambient light.
14. Common example of Rangesensors
❖Infrared sensors
❖Sonar range finders (Ultrasonic sensors)
❖LIDAR sensors
15. Infrared Distance Sensors
IR distance sensor does distance or proximity sensing through
emitting IR wave and calculating the angle of reflection.
IR sensors come with two lenses:
• An IR LED emitter lens that emits a light beam
• A position-sensible photodetector (PSD) where the reflected beam
will fall onto
IR Distance Sensors: Working Principle
IR distance sensors work through the principle of
triangulation; measuring distance based on the angle of the
reflected beam.
17. IR Sensor (cont)
An illustration of how IR distance sensors work
through triangulation:
18. IR Sensor (cont)
Description of illustration
1.Infrared light is emitted from the IR LED emitter
2.The beam of light hits the object (P1) and is
reflected off a certain angle
3.The reflected light will reach the PSD (U1)
4.The sensor in the PSD will then determine the
position/distance of the reflective object
19. Key Applications for IRSensors
•TVs, computers, laptops
•Distance measurement
•Security systems such as surveillance, burglar
alarms, etc.
•Monitoring and control applications
20. Advantages and Disadvantages of IRSensors
Advantages
•Small form factor; Common IR sensors are smaller in size
•Applicable for daytime and nighttime usages
•Secured communication through a line of sight
•Able to measure the distance of objects that have complex
surfaces unlike ultrasonic sensors
Disadvantages of IR sensors
•Limited measurement range
•Affected by environmental conditions and hard object
21. Sonar range finders (Ultrasonicsensors)
❖Ultrasonic sensors Accurately measure
distances over a wide range
24. Calculating distance using Ultrasonicsensor
Distance = (Time x SpeedOfSound) / 2. The "2" is in the formula because the
sound has to travel back and forth.
Speed of sound at sea level = 343 m/s or 34300 cm/s
25. Key applications of Ultrasonicsensors
• Distance Measurement
• Robotic Sensors
• Smart cars –Tesla uses ultrasonic sensors as part of its
Autopilot program
• Unmanned Aerial Vehicles (UAV) / Drones
26. Advantages and disadvantages ofUltrasonic
sensors
Advantages of Ultrasonic Sensors
• Not affected by object color and transparency as it detects
distance through sound waves
• Works well in places that are dim
• Tend to consume lower current/power
• Multiple interface options for pairing with a microcontroller,
etc.
Disadvantages of Ultrasonic Sensors
• Limited detection range
• Low resolution and slow refresh rate, making it not suitable for
detection of fast-moving targets
• Unable to measure the distance of objects that have extreme
textures/surfaces
28. LiDAR Sensor
❖Lidar stand for “Light Detection And Ranging.”
❖It is sometimes called “laser scanning” or “3D
scanning.”
❖The technology uses eye-safe laser beams to create a
3D representation of the surveyed environment.
❖It measures the range of targets through light waves
from a laser instead of radio or sound waves.
30. LiDAR : WorkingPrinciple
❖A typical lidar sensor emits pulsed light waves into
the surrounding environment.
❖These pulses bounce off surrounding objects and
return to the sensor. The sensor uses the time it took
for each pulse to return to the sensor to calculate
the distance it traveled.
❖Repeating this process millions of times per second
creates a precise, real-time 3D map of the
environment. A robot can utilize this map for safe
navigation.
32. LiDAR : Working Principle(cont)
1.The transmitter on the LiDAR device emits laser
light at the target object
2.The pulse of the laser is reflected by the target
object
3.Distance is then calculated by using the
relationship between constant speed of light in air
and the time between sending/receiving of the
signal
33. Key Applications ofLiDAR
•Environmental Monitoring; forestry, land
mapping, etc.
•Distance Measurement
•Machine Control and Safety
•Robotics Imaging & Environmental Detection
34. Advantages and Disadvantages ofLiDAR
Advantages of LiDAR
• High measurement range and accuracy
• Ability to measure 3D structures
• Fast update rate; suitable for fast-moving objects
• Small wavelengths as compared to sonar and radar; good at
detecting small objects
• Applicable for usage in the day and night
Disadvantages of LiDAR
• Higher cost as compared to ultrasonic and IR
• Harmful to the naked eye; higher-end LiDAR devices may utilize
stronger LiDAR pulses which may affect the human eye
35. LED Time-Of-Flight Distance Sensors
❖The Time-of-Flight principle (ToF) is a method
for measuring the distance between a sensor
and an object, based on the time difference
between the emission of a signal and its return
to the sensor, after being reflected by an
object
37. Time-of-Flight Sensors: WorkingPrinciple
Time-of-Flight sensors measure the elapsed time from the
emission of a wave pulse from the sensor to the moment it
returns to the sensor after reflecting off an object.
It is capable of producing a 3D X, Y,Z image with a single
snapshot by measuring the time it takes for light to travel from
emitter to the receiver.
With time-of-flight technology, it provides significant benefits
over other distance sensing methods (IR, Ultrasonic)
• Wider range
• Faster readings
• Greater accuracy
39. Time-of-Flight Sensors: Working Principle(cont)
Time-of-flight sensors work similarly to LiDAR sensors,
where:
1.The transmitter on the time-of-flight device emits IR
waves towards the target object
2.The wave is reflected back upon reaching the target
object
3.Distance is then calculated by using the speed of
light in air and the time between sending/receiving of
the signal
41. Advantages and Disadvantages
Advantages of Time-of-Flight Sensors
• Such technology offers high measurement range with accuracy
• 3D imaging capable
• Used in a wide variety of applications due to its ability to
identify large objects
Disadvantages of Time-of-Flight Sensors
• Higher costs in general
• Z-depth resolution is still poor with general systems offering a
1cm Z-resolution
43. TACTILE SENSORS
❖ Tactile sensors provide the robot with the
capability to respond to contact forces
between itself and other objects within its
work volume.
❖ Potential use of robots with tactile sensing
capabilities would be in assembly and
inspection operations.
❖ Tactile sensors can be divided into two types:
• Touch sensors
• Stress sensors
44. Touch Sensors
A touch sensor is a type of device that captures and
records physical touch or embrace on a device and/or
object.
It enables a device or object to detect touch or near
proximity, typically by a human user or operator are
sensitive to touch, force or pressure.
Touch sensors are used simply to indicate whether contact
has been made with an object.
A simple micro switch can serve the purpose of a touch
sensor.
47. Applications of Touchsensors
•Touch sensor in robotics; a touch sensor is commonly
used in robots, enabling basic movement and the ability
to detect touch in its surroundings (E.g. When the robot
runs into something, the touch sensor can have it to stop
moving)
•Smartphones, automotive, industrial applications
•Touch sensor faucet in kitchens; allowing for control of
running water without having to physically turn the knob
•Most other applications that require pressure/distance
measurement
48. Two main Types of Touchsensors
1. Capacitive touch sensor
2. Resistive touch sensor
49. Touch sensors-Capacitive touch sensor
How capacitive touch sensor work:
1.The user applies touch on the glass panel
2.The printed circuit panel around the outer viewing area of the glass panel
creates an electrical charge across the surface
3.It results in a decrease in capacitance and allows the system to
determine the touchpoint
4.Multiple touchpoints can be detected as well, allowing for touch pinch
and spread
Capacitive touch sensor applications:
•Portable devices such as smartphones and tablets (iPhones, iPad, etc.)
•Home applications such as touch lamps
•Automotive
•Industrial
50. Advantages and disadvantages ofCTS
Advantages of a capacitive touch sensor:
• Doesn’t require pressure to be applied since
it is built on the glass itself, hence making force insignificant to
sensing requirements
• Support for multi-touch
• High responsiveness
Disadvantages of a capacitive touch sensor:
• Vulnerable to abrasion (wearing due to friction)
• Reliability concerns when used in harsh environments
• Doesn’t work with gloves or stylus
51. Touch sensors-Resistive touch sensor
❖ Resistive touch sensor measures touch through responding to the
pressure applied to their surface.
❖ It consists of two conductive layers and a non-conductive separator.
Unlike the capacitive touch sensors, it’s not multi-touch compatible.
How resistive touch sensor work:
1.The user applies pressure against the surface
2.The outside conductive layer is then pressed against the inner layer,
resulting in voltage changes
3.The voltage changes are then compared to the starting voltage, allowing
for the point at which the touch took place to be calculated
53. Advantages and disadvantages of ResistiveTS
Advantages of a resistive touch sensor:
• Cost-effective and durable to be used in harsh environments
• Able to be used with stylus and gloves
• Less complex
• Low power consumption
Disadvantages of a resistive touch sensor:
• The inability for multi-touch technology unlike the capacitive
touch sensors
• Dependent on pressure, require more pressure to be applied for
sensing to take place
56. Voice sensors
▪ Another area of robotics research is voice sensing or voice programming
▪ Voice programming -- the oral communication of commands to the robot
or other machine.
▪ The robot controller is equipped with a speech recognition system which
analyzes the voice input and compares it with a set of stored word
patterns when a match is found between the input and the stored
vocabulary word the robot performs some actions which corresponds to
the word.
▪ Voice sensors could be useful in robot programming to speed up the
programming procedure.
▪ It would also be beneficial in especially in hazardous working
environments for performing unique operations such as maintenance and
repair work.
▪ The robot could be placed in hazardous environment and remotely
commanded to perform the repair chores by means of step by step
instructions.
58. INTERNALSENSORS
❖ Internal sensors measure the robot's internal state.
❖ They are used to measure its position, velocity and
acceleration.
❖ Categories
❖ Position sensors
❖ Velocity sensors
❖ Acceleration Sensors
❖ Axis of acceleration
59. Position sensor
Position sensors measure the position of a joint (the degree to
which the joint is extended). They include:
Encoder: a digital optical device that converts motion into a
sequence of digital pulses.
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.
61. Velocity Sensor
A velocity or speed sensor measures consecutive position measurements at known
intervals and computes the time rate of change in the position values.
62. Acceleration Sensors
An accelerometer measures acceleration (change in speed)
of anything that it's mounted on
Acceleration sensors or accelerometers let you make
precise measurements of vibration or shock for a variety
of applications.
They are used to measure vibration, shock, displacement,
velocity, inclination and tilt.
All sensors are highly resistant against shock and vibration
and are suitable for a wide range of purposes.
64. Possible uses for accelerometers inrobotics
❑Tilt-mode game controllers
❑Self balancing robots
❑Model airplane auto pilot
❑Alarm systems
❑Collision detection
❑Human motion monitoring
❑Vibration Detectors for Vibration Isolators
❑G-Force Detectors
