Sensors and Actuators for Robotics
23RIPC210
Course Outcomes
Module 1: Fundamentals & Performance
Introduction, Definitions, Classification of sensors and activators, General requirements for interfacing, Performance characteristics of sensors and activators, Input and Output characteristics
Textbook 1: 1.1-1.5, 2.1-2.2
Textbooks:
1.Nathan Ida, Sensors, Actuators, and Their Interfaces A multidisciplinary introduction 2nd Edition,2020, IET, Control, Robotics and Sensors Series 127.
2.D. Patranabis, Sensors and Transducers, PHI Learning Pvt. Ltd.
The senses �
The senses �
The senses �
The senses �
The senses �
The senses �
Introduction
Introduction
Example | Sensor | Actuator | Hidden Truth |
Car Engine | Coolant temp sensor | N/A | Not engine temp—drivers clueless on location! |
Airbag | Accelerometers (deceleration) | Explosive gas charge | Processor decides; uses familiar explosives. |
Catalytic Converter | Gas sensors | Chemical conversion | Turns pollution benign—under the car? |
Home Thermostat | Bimetal/mercury switch | Furnace/AC | Primitive in cheap models; vague sensor spot. |
Jar Lid | Pressure sensor | N/A | Pop-up detects spoilage—most common daily! |
A short historical note �
A short historical note �
A short historical note �
A short historical note �
A short historical note �
A short historical note �
Definitions �
Definitions �
Definitions �
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A device that responds to a physical stimulus and transmits a resulting impulse. (Webster’s New Collegiate Dictionary, 1998)
Problem: What is an impulse? Does every sensor “transmit” an impulse?
A device, such as a photoelectric cell, that receives and responds to a signal or stimulus. (American Heritage Dictionary, 3rd ed., 1996)
Problem: The definition uses an example (photoelectric cell) that may not be representative of all sensors. What does “receives” mean?
A device that responds to a physical stimulus (as heat, light, sound, pressure, magnetism, or a particular motion) and transmits a resulting impulse (as for measurement or operating a control). (Webster’s New World Dictionary, 3rd ed.,
1999)
Problem: What is “impulse” and why “as for measurement or operating a control”? �
Definitions �
A device that is actuated by power from one system and supplies power usually in another form to a second system. (Webster’s New Collegiate Dictionary, 1998)
Problem: Why “power” and is a transducer an actual physical device?
A substance or device, such as a piezoelectric crystal, that converts the input energy of one form into the output energy of another (from: trans-ducere—to transfer, to lead) (American Heritage Dictionary, 3rd ed., 1996)
Problem: What is meant by “substance” and “input energy”? Is the example of the piezoelectric crystal appropriate and representative?
A device that is actuated by power from one system and supplies power usually in another form to a second system (a loudspeaker is a transducer that transforms electrical signals to sound energy). (Webster’s New World Dictionary,
3rd ed., 1990)
Problem: Is the loudspeaker a transducer or does transduction occur in the loudspeaker as part of its function?
Definitions �
A mechanism for moving or controlling something indirectly instead of by hand. (Webster’s New Collegiate Dictionary, 1998)
Problem: Does it require specifically a motion? Does that mean that a direct control such as in a thermostat does not qualify as actuation?
One that activates, especially a device responsible for actuating a mechanical device such as one connected to a computer by a sensor link. (American Heritage Dictionary, 3rd ed., 1996)
Problem: Does an actuator have to be a mechanical device (see first definition)? An example is given, but is it appropriate as a definition?
One that actuates; a mechanical device for moving or controlling something. (Webster’s New World Dictionary, 3rd ed., 1990)
Problem: Does it have to be a mechanical device? Does it have to move or control something
Definitions �
The terms sensor, actuator, and transducer are often used interchangeably, leading to confusion.
A transducer may represent: A sensor, An actuator, or A system containing sensing, energy conversion, and signal-conditioning elements. Example: Loudspeaker Converts electrical energy → sound energy → acts as an actuator. Can also work as a microphone converting sound → electrical signal → acts as a sensor.
Many devices exhibit duality, functioning both as sensors and actuators.
The difference mainly lies in power levels: Actuators deliver higher power. Sensors typically generate or measure small signals.
Therefore, multiple definitions exist, and all can be correct depending on application context.
Definitions �
Consider a magnetic loudspeaker used as a microphone: Cone motion moves a coil in a magnetic field. Generates voltage and current without external power. Example of a passive sensor.
Energy transduction occurs: Sound pressure → Electrical signal Electrical signal → Sound waves
Two loudspeakers can communicate directly: One acts as sensor, the other as actuator.
Similar principle seen in tin-can string communication: Sound waves ↔ Mechanical vibrations.
In practical systems: Direct connection is uncommon. A processing element (amplifier/signal conditioning) is required between sensor and actuator.
Typical system flow: Sensor → Signal Processing → Actuator
Definitions �
Definitions �
Following this rather long introduction, the definitions we will use are as
follows:
Sensor
A device that responds to a physical stimulus.
Transducer
A device or mechanism that converts power of one form into power of another form.
Actuator
A device or mechanism capable of performing a physical action or effect. �
Classification of sensors and actuators �
Classification of sensors and actuators �
1. Active and Passive Sensors
Active Sensors
Passive Sensors (Self-Generating)
Classification of sensors and actuators �
2.Contact and Non-Contact Sensors
Classification of sensors and actuators �
3. Absolute vs Relative Sensors
Absolute Sensors
Measure with respect to an absolute reference.
Example: Thermistor (absolute temperature).
Relative Sensors
Measure differences between two quantities.
Example:Thermocouple → temperature difference
Pressure sensor → pressure difference
Classification of sensors and actuators �
Sensors may also be categorized based on:
Classification of sensors and actuators �
Actuators typically:
Produce motion, Apply force, Generate physical effects.
Classified based on:
Type of motion,
Operating physical principle,
Energy conversion method.
Classification of sensors and actuators �
Classification of sensors and actuators �
Classification of sensors and actuators �
General requirements for interfacing �
General requirements for interfacing �
A complete system for sensing of temperature and activation of a fan to cool a device �
Performance characteristics of sensors�and actuators �
Input and output characteristics �
Transfer Function
Describes the mathematical relationship between:
Input → Output
Applicable to both sensors and actuators regardless of signal type.
Inputs and outputs may be:
Electrical
Mechanical
Thermal
Chemical
Input and output characteristics �1.Transfer Function
Also called:
Transfer characteristic
Input–Output characteristic
Device response
It defines the relationship between input and
output of a sensor or actuator.
aT + b = R �
Input and output characteristics �2. Impedance and impedance matching
Input and output characteristics �3. Range, span, input and output full scale, resolution, and dynamic range
Input and output characteristics �3. Range, span, input and output full scale, resolution, and dynamic range
Input and output characteristics �4.Accuracy, errors, and repeatability
Repeatability, sometimes called reproducibility, of sensors and actuators is an important design characteristic and simply indicates the failure of the sensor or actuator to represent the same value.
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Input and output characteristics �5.Sensitivity and sensitivity analysis
Ex- For the linear transfer function �
Input and output characteristics �5.Sensitivity and sensitivity analysis
The three transducers are connected in series and their errors are additive. The sensitivity of each element is �
where yi is the output of transducer i and xi is its input. Suppose first that there are no errors in the system. Then, we can write �
But clearly, x2 = y1 (the output of transducer 1 is the input to transducer 2) and x3 = y2. With these we get �
Input and output characteristics �5.Sensitivity and sensitivity analysis
Assuming first that there are no errors and that each transducer has a different transfer function, the sensitivity of
each sensor is �
Input and output characteristics �5.Sensitivity and sensitivity analysis
Input and output characteristics �6. Hysteresis, nonlinearity, and saturation
Hysteresis
Nonlinearity
Input and output characteristics �6. Hysteresis, nonlinearity, and saturation
Saturation
Input and output characteristics �7. Frequency response, response time, and bandwidth
Points A and B Related to
Input and output characteristics �8, Calibration
Input and output characteristics �9.Excitation
Excitation refers to the electrical supply required for operation of a sensor or actuator. �
10. Deadband
Deadband is the lack of response or insensitivity of a device over a specific range of the input. In this range, which may be small, the output remains constant �
11.Reliability �
Reliability is a statistical measure of the quality of a device that indicates the ability of the device to perform its stated function, under normal operating conditions, without failure, for a stated period of time or number of cycles. �