This document discusses types of electric motors and sensors used in robotics. It describes DC, servo, and stepper motors, including their specifications and control. Variable reluctance, permanent magnet, and hybrid stepper motors are defined. Selection criteria for actuators include continuous power output, resolution, and heat dissipation. Sensors for localization, navigation, obstacle avoidance, and path planning are also covered, including optical, inertial, thermal, chemical, and biosensors. Case studies on sensor and actuator selection for maze solving robots and self-driving cars are mentioned.

1. UNIT II BUILDING BLOCKS OF A ROBOT

2. • Types of electric motors -
• DC, Servo, Stepper; specification, drives for motors - speed &
direction control and circuitry,
• Selection criterion for actuators, direct drives, non-traditional
actuators;
• Sensors for localization, navigation, obstacle avoidance and path
planning in known and unknown environments –
• optical, inertial, thermal, chemical, biosensor, other common
sensors;
• Case study on choice of sensors and actuators for maze solving
robot and self driving cars

4. Types of electric motors
• Definition for Electrical drives
–An electrical drive can be defined as an
electromechanical device for converting
electrical energy into mechanical energy to
impart motion to different machines and
mechanisms for various kinds of process
control.

5. VARIOUS TYPES OF MOTORS
• 1. Stepper motor
– 1.1 Variable Reluctance Motor
– 1.2 Permanent magnet (PM) stepper motor
– 1.3 Hybrid stepper motor
• 2. Servomotor
– 2.1 DC servomotors
– 2.2. AC servo motor

6. Stepper motor
A stepper motor, also known as
step motor or stepping motor, is a
brushless DC electric motor that
divides a full rotation into a
number of equal steps.

7. Stepper Motor

8. Application of Stepper Motor

11. Variable Reluctance Motor
• It has four rotor teeth, 90⁰ apart and six stator poles, 60⁰ apart.
• Electromagnetic field is produced by activating the stator coils in
sequence. It attracts the metal rotor.
• When the windings are energized in a reoccurring sequence of 2, 3, 1,
and so on, the motor will rotate in a 30⁰ step angle.
• In the non-energized condition, there is no magnetic flux in the air gap,
as the stator is an electromagnet and the rotor is a piece of soft iron;
hence, there is no detent torque.
• This type of stepper motor is called a variable reluctance stepper.

12. Variable Reluctance Motor

14. Permanent magnet (PM) stepper
motor
• In this type of motor, the rotor is a permanent magnet. Unlike
the other stepping motors, the PM motor rotor has no teeth
and is designed to be magnetized at a right angle to its axis.
• Applying current to each phase in sequence will cause the
rotor to rotate by adjusting to the changing magnetic fields.
• Although it operates at fairly low speed, the PM motor has a
relatively high torque characteristic. These are low cost motors
with typical step angle ranging between 7.5⁰ to 15⁰ .

15. Permanent magnet (PM) stepper
motor

17. Hybrid stepper motor
• Hybrid stepping motors combine a permanent
magnet and a rotor with metal teeth to
provide features of the variable reluctance
and permanent magnet motors together.
• The number of rotor pole pairs is equal to the
number of teeth on one of the rotor's parts.
• The hybrid motor stator has teeth creating
more poles than the main poles windings

18. Hybrid stepper motor

20. Servomotor
• A servo is a small motor that you can position
at any angle very accurately.
• It contains internal circuits that will
automatically maintain that particular angle.
• However, you cannot do full revolutions with a
servo. You are restricted to a certain range,
usually from 180-270 degrees.

21. Servomotor

23. Performance Specifications
• Shaft speed (RPM)
• Terminal voltage
• Torque
– Starting torque
– Continuous torque

24. Controller

25. Actuator
• An actuator is a component of a machine that
is responsible for moving and controlling a
mechanism or system, for example by opening
a valve.
• In simple terms, it is a "mover". An actuator
requires a control signal and a source of
energy.

27. SELECTION CRITERIAN FOR
ACTUATORS
• The selection of the proper actuator is more
complicated than selection of the sensors,
primarily due to their effect on the dynamic
behavior of the overall system.
• Furthermore, the selection of the actuator
dominates the power needs and the coupling
mechanisms of the entire system.

28. SELECTION CRITERIAN FOR
ACTUATORS
1. Continuous power output—The maximum force/torque attainable continuously
without
exceeding the temperature limits
2. Range of motion—The range of linear/rotary motion
3. Resolution—The minimum increment of force/torque attainable
4. Accuracy—Linearity of the relationship between the input and output
5. Peak force/torque—The force/torque at which the actuator stalls
6. Heat dissipation—Maximum wattage of heat dissipation in continuous operation
7. Speed characteristics—Force/torque versus speed relationship
8. No load speed—Typical operating speed/velocity with no external load
9. Frequency response—The range of frequency over which the output follows the
input faithfully, applicable to linear actuators
10. Power requirement—Type of power (AC or DC), number of phases, voltage level,
and current capacity

29. Direct drives
• A direct drive mechanism is one that uses the
torque coming from a motor without any
reductions (such as a gearbox).
• The load is connected directly to the motor,
without mechanical transmission elements
such as gearboxes or belt and pulley systems.
In other words, the motor directly drives the
load.

32. Non-traditional actuators

33. Sensors for localization
• Robot localization is the process of determining
where a mobile robot is located with respect to
its environment.
• Localization is one of the most fundamental
competencies required by an autonomous
robot.
• Location is an essential precursor to making
decisions about future actions.

34. Sensors for localization
• Encoder
• Position prediction
• Observation
• Matching
• Estimation
• Odometry

35. Robot Sensors - localization
 Infrared Ranging
 Magnetometer
 GPS
 IR Modulator
 Receiver
 Accelerometer
 Camera
 Linear Encoder
 Sonar Ranging
 Gyroscope
 Rotary
 Encoder
 Laser triangulation
 Laser Rangefinder
 Compass

36. NAVIGATION
• Navigation and guidance are defined as the
processes of determining and controlling the
position of a vehicle.
• An autonomous system will have to include
these two basic procedures to perform any
useful task.
• The information generally required for
navigation is the direction, speed, and
position of the vehicle.

37. Navigation Sensors
• Dead Reckoning Sensors
– Dead reckoning sensors measure quantities such as position, velocity,
acceleration and orientation.
Potentiometers
Encoders
Incremental Encoders
Absolute Encoders
Linear Variable Differential Transformers (LVDT)
Synchros and Resolvers
Compass
Inertial Sensors
Accelerometers
Gyroscopes

38. Navigation Sensors
• Behavior-based navigation
• Model Based System (also called map-based)

39. Behavior-based navigation
• It does not use any map; it simply depends on
received signal strength indication (RSSI) to
approach the sensor node that sent signal.

40. Behavior-based navigation

41. Model Based System
• The model-based navigation systems consist
of four phases, namely
– perception,
– localization,
– planning and
– motion control.

42. Model Based System

43. Model Based System
• In contrast to the behavior-based approach, the
model-based (also called map-based) approach
includes both localization and planning modules;
besides, it is organized in a hierarchical fashion.
1. First - Input from sensors - location of walls,
doors, obstacles, and people (perception).
2. Secondly - Use Local Maps Stored in it.
3. Thirdly - path-planning algorithms.
4. Finally - sends outputs to the actuators.

44. Obstacle avoidance and path planning
in known and unknown
environments

45. Obstacle avoidance and path planning
• A new path planning method for Mobile Robots
(MR) has been developed and implemented.
• On the one hand, based on the shortest path
from the start point to the goal point, this
path planner can choose the best moving
directions of the MR, which helps to reach the
target point as soon as possible.

46. • PATH PLANNING
• Path planning involves identifying a trajectory that will cause the
robot to reach the goal location when executed. Path planning is a
strategic problem-solving competence, as the robot must decide
what to do over the long term to achieve its goals.
• OBSTACLE AVOIDANCE
• The second competence is equally important but occupies the
opposite, tactical extreme. Given real-time sensor readings,
obstacle avoidance means modulating the trajectory of the robot in
order to avoid collisions.

50. SENSORS
• Optical,
• Inertial,
• Thermal,
• Chemical,
• Biosensor,
• other common sensors;

51. Optical sensors

53. Light sensors
• Light falling on to the surface of a light sensor generates
an electrical output proportional to the strength of the
incident illumination.
• The sensor responds to a band of radiant energy existing
within a narrow range of frequencies in the
electromagnetic spectrum, which we characterize as light.
• These frequencies range from the infrared to the visible
and continue to the ultraviolet region of the spectrum.

54. Optical sensors
• Most light sensors are passive devices for
converting the light energy of the spectrum into
electrical signal.
• Light sensors are also known as photo sensors or
photoelectric devices, since they convert photons
into electrons.

55. Optical sensors
• We can group photoelectric devices into two main
categories.
– 1. One generates electricity when illuminated – such as
photovoltaic or photo-emissive, Solar Panel etc.
– 2.The other changes their electrical properties in some
way – such as LED photo-resistors or photo-conductors,
etc.

56. Types of Optical sensors
• Photovoltaic - Photovoltaic light sensors are also called solar
cells.
• Light Dependent- Light-dependent sensors are inexpensive
and commonly used for gauging and responding to light levels.
• Photo Diode - Digital technology like cameras, video recorders and
remote controls use photo diodes to detect light levels ranging from infrared to
the visible spectrum.
• Proximity - Proximity light sensors respond to changes in infrared light
to detect motion or proximity to another object.

57. Photodiode
It is a semiconductor device with PN junction and this PN junction
layer found in between the P-type semiconductor and N-type
semiconductor. It is designed to work in the reverse bias mode.
Applications
 Detection of both visible and invisible light
rays.
 Used in digital and logic circuit.
 Used in optical fibre communication system.

58. Phototransistor
• Phototransistor converts the striking light into photocurrent. In this sensor,
the light rays are used to illuminate the junction region (base region) instead
of providing base current. It is consist of three terminal, base, emitter, and
collector. Base terminal is made up of the very special material which is
sensitive to the light.
Applications
Counting system
Encoder sensing
Object detection
Ambient light detection
Remote controller
Read finger position

59. Photoresistor
It is also known as the light dependent resistor. It
depends on the resistor, the flow of the current
increases in photoresistor when the intensity of light
increases.
Applications
 Used to on and off the street light and it reduces the
wastage of the electricity.
 Compare the relative light level.
 Light meters in camera.
 Used to control the reduction in gain of the dynamic
compressor.
 Infrared detectors.

60. Inertial Sensors
• Inertial sensors are sensors based on inertia
and relevant measuring principles.
• These range from Micro Electro Mechanical
Systems (MEMS) inertial sensors, measuring
only few mm, up to ring laser gyroscopes that
are high-precision devices with a size of up to
50cm.

70. Thermal sensors
• A device that detects temperature. Thermal
sensors are found in many laptops and
desktop PCs in order to sound an alarm when
a certain temperature has been exceeded.

71. PIR Sensors
Infrared sensors receive heat
radiated from the human body.
Segment lenses divide the
detection zone into passive and
active zones. This way, the highly
sensitive sensors can detect
persons or warm objects moving
between the zones as a change
in voltage.

72. Temperature sensors
• Contact Temperature Sensor
Types –
– These types of temperature
sensor are required to be in
physical contact with the object
being sensed and use
conduction to monitor changes
in temperature. They can be
used to detect solids, liquids or
gases over a wide range of
temperatures.
• Non-contact Temperature
Sensor Types –
– These types of temperature
sensor use convection and
radiation to monitor changes in
temperature. They can be used
to detect liquids and gases that
emit radiant energy as heat
rises and cold settles to the
bottom in convection currents
or detect the radiant energy
being transmitted from an
object in the form of infra-red
radiation (the sun).

73. Temperature sensors
• Thermostat
• Thermistor
• Thermocouple
• Resistance Temperature Detectors (RTD)

74. Thermostat
• The Thermostat is a contact type
– electro-mechanical temperature sensor or switch, that
basically consists of two different metals such as nickel,
copper, tungsten or aluminium etc, that are bonded together
to form a Bi-metallic strip.

75. Thermistor
• The Thermistor is another type of temperature
sensor, whose name is a combination of the words
THERM-ally sensitive res-ISTOR.
• A thermistor is a special type of resistor which
changes its physical resistance when exposed to
changes in temperature.
• Most types of thermistor’s have a Negative
Temperature Coefficient of resistance or (NTC),
that is their resistance value goes DOWN with an
increase in the temperature, and of course there
are some which have a
, in that their resistance value
goes with an increase in temperature.

76. Thermistor

77. Thermocouples
• If two different metals ‘A’ and ‘B’ are connected as in Figure,
with a junction and a voltmeter, then if the junction is heated the
meter should show a voltage.
• This is known as the Seebeck effect.

78. Construction of Thermocouples
• At the tip of a grounded junction probe, the thermocouple wires are
physically attached to the inside of the probe wall. This results in good
heat transfer from the outside, through the probe wall to the thermocouple
junction.
• In an ungrounded probe, the thermocouple junction is detached from the
probe wall. Response time is slower than the grounded style, but the
ungrounded offers electrical isolation.
• The thermocouple in the exposed junction style protrudes out of the tip of
the sheath and is exposed to the surrounding environment. This type offers
the best response time, but is limited in use to dry, non-corrosive and non-
pressurized applications.

79. Types of thermocouples
Sr.
No
Type Thermocouple Material Sensitivit
y in
(µV/oC)
Useful
temperature
range 0C
1 T Copper-Constantan 20 – 60 -180 to +400
2 J Iron-Constantan 45 – 55 -180 to +850
3 K Chromel-Alumel 40 – 55 -200 to +1300
4 E Chromel-Constantan 55 – 80 -180 to +850
5 S Platinum-Platinum/10% Rhodium 5 – 12 0 to +1400
6 R Platinum-Platinum/13% Rhodium 5 – 12 0 to +1600
7 B Platinum/ 30% Rhodium-Platinum/6% Rhodium 5 – 12 +100 to +1800
8 W5 Tungsten/5% Rhenium-Tungsten/20% Rhenium 5 – 12 0 to +3000
Constantan = copper/nickel; Chromel = nickel/chromium; Alumenl = nickel/aluminium

80. Selection of Thermocouples
The following criteria are used in selecting a thermocouple:
– Temperature range
– Chemical resistance of the thermocouple or sheath
material
– Abrasion and vibration resistance
– Installation requirements (may need to be
compatible with existing equipment; existing
holes may determine probe diameter)

81. Resistance Temperature Detector
(RTD)
Uses the phenomenon that the resistance of a metal changes with
temperature.
Are linear over a wide range and most stable.

82. Resistance Temperature Detector
(RTD)
Uses the phenomenon that the resistance of a metal changes with
temperature.
Are linear over a wide range and most stable.

83. Advantages of platinum as RTD
• The temperature-resistance characteristics of
pure platinum are stable over a wide range of
temperatures.
• It has high resistance to chemical attack and
contamination
• It forms the most easily reproducible type of
temperature transducer with a high degree of
accuracy .
• It can have accuracy ± 0.01 oC up to 500 oC and
± 0.1 oC up to 1200 oC.

84. Limitations of RTD
• These are resistive devices, and accordingly they function by passing a
current through a sensor.
• Even though only a very small current is generally employed, it creates a
certain amount of heat and thus can throw off the temperature
reading.
• This self heating in resistive sensors can be significant when dealing
with a still fluid (i.e., one that is neither flowing nor agitated), because
there is less carry-off of the heat generated.
• This problem does not arise with thermocouples, which are essentially
zero-current devices.

85. Comparison: Thermocouple vs RTD

86. Biosensors
• Biosensors are devices comprising a biological
element and a physiochemical detector that
are used to detect analytes.
• These instruments have a wide range of
applications ranging from clinical through to
environmental and agricultural. The devices
are also used in the food industry.

88. Applications
• General healthcare monitoring
• Screening for disease
• Clinical analysis and diagnosis of disease
• Veterinary and agricultural applications
• Industrial processing and monitoring
• Environmental pollution control

89. Other common sensors
• Light sensors.
• Sound Sensor. ...
• Temperature Sensor. ...
• Contact Sensor. ...
• Proximity Sensor. ...
• Distance Sensor. ...
• Pressure Sensors. ...
• Tilt Sensors
• Potentiometer
• LVDT
• Encoders
• Capacitance sensors
• Strain gauges
• Eddy current sensor
• Hall effect sensor
• Light sensors

90. • Case study on choice of sensors and actuators
for maze solving robot and self driving cars

91. Maze solving robot

94. Self driving cars Sensors
• The three primary autonomous vehicle
sensors are camera, radar and lidar.
• Working together, they provide the car visuals
of its surroundings and help it detect the
speed and distance of nearby objects, as well
as their three-dimensional shape.