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Robotics Sensors and Actuators

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Module 1: Sensor classifications and characteristics

  1. Q1a. Which of the following sensors is primarily used to detect the presence of an object without physical contact, often utilizing infrared radiation to measure proximity? (i) Tactile sensor (ii) Photodiode (iii) Collision sensor (iv) IR proximity sensor20242m

    Module 1: Sensor classifications and characteristics

    Which of the following sensors is primarily used to detect the presence of an object without physical contact, often utilizing infrared radiation to measure proximity?
    (i) Tactile sensor
    (ii) Photodiode
    (iii) Collision sensor
    (iv) IR proximity sensor

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    Answer

    Correct Option: (iv) IR proximity sensor

    Explanation

    IR proximity sensor detects presence without physical contact by emitting infrared radiation and measuring reflected IR intensity / time-of-flight.

    • Tactile sensor → requires contact (force/pressure).
    • Photodiode → detects light intensity, not specifically proximity.
    • Collision sensor → contact/impact detection.

    IR proximity (and also ultrasonic) uses IR LED + photodiode pair; distance ∝ reflected intensity.

    Final Answer

    IR proximity sensor → Option (iv).

  2. Q1b. A Sensor is a: (i) Subsystem (ii) Module (iii) Machine (iv) All the above20242m

    Module 1: Sensor classifications and characteristics

    A Sensor is a:
    (i) Subsystem
    (ii) Module
    (iii) Machine
    (iv) All the above

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    Answer

    Correct Option: (i) Subsystem (also accepted as (ii) Module — sensor is a modular subsystem)

    Explanation

    Sensor: Device/subsystem that converts physical stimulus (light, force, proximity, temperature) into electrical signal measurable by controller.

    • Subsystem: Part of larger robot system that performs sensing.
    • Module: Sometimes called sensing module (self-contained).
    • Machine: Complete robot or actuator system, not just sensor.
    • All the above: Incorrect because sensor alone is not a complete machine.

    In robotics hierarchy: Robot System → Subsystems (Sensing, Actuation, Control) → Modules. Sensor belongs to sensing subsystem.

    If exam key expects most general, (i) Subsystem (or (ii) Module if they treat module=subsystem). Some keys mark (iv) All the above as sensor can be viewed at any abstraction, but technically Subsystem is precise.

    Final Answer

    Sensor is a Subsystem (modular sensing unit) → Option (i) (acceptable as (ii) Module).

  3. Q1d. Which of the following is considered as input to a sensor? (i) Microcontroller (ii) Passive IR sensor (iii) Processor (iv) Drivers20242m

    Module 1: Sensor classifications and characteristics

    Which of the following is considered as input to a sensor?
    (i) Microcontroller
    (ii) Passive IR sensor
    (iii) Processor
    (iv) Drivers

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    Answer

    Correct Concept: Physical measurand (e.g., IR radiation, temperature, force) is the true input to a sensor — none of (i)-(iv) is a physical stimulus. If forced to choose from given options, the intended exam key is often (iv) Drivers (excitation/drivers provide operating input) or (ii) Passive IR sensor as example, but technically the question is flawed.

    Explanation

    Sensor model: Physical stimulus → Sensor → Electrical signal → Conditioning → Microcontroller/Processor.

    • Input to sensor: Physical phenomenon (light, heat, pressure, proximity, magnetic field).
    • Output from sensor: Electrical signal (voltage/current/resistance change) sent to microcontroller/processor.
    • Drivers: Provide excitation/power to active sensors, not measurand.
    • Passive IR sensor: Itself a sensor (detects IR), not input to another sensor.
    • Microcontroller/Processor: Receives sensor output, not input to sensor.

    Hence strictly none of (i)-(iv) is the measurand input. In many university keys, they treat “Drivers / excitation circuit” as the electrical input that powers the sensor, so (iv) Drivers is marked, or they mistakenly list (ii) Passive IR sensor as example of sensor type.

    Final Answer

    True input = physical stimulus (IR, force, etc.). Among options, (iv) Drivers (excitation) is closest as electrical input; otherwise the question is ambiguous and none correctly describes the measurand input.

  4. Q1e. An IR sensor that only detects IR radiation but does not emit is called: (i) Active IR sensor (ii) Passive IR sensor (iii) Both a and b (iv) Resistive IR sensor20242m

    Module 1: Sensor classifications and characteristics

    An IR sensor that only detects IR radiation but does not emit is called:
    (i) Active IR sensor
    (ii) Passive IR sensor
    (iii) Both a and b
    (iv) Resistive IR sensor

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    Worked Solution

    Answer

    Correct Option: (ii) Passive IR sensor

    Explanation

    • Active IR: Has emitter (IR LED) + detector (photodiode). Emits IR, measures reflection (proximity, distance).
    • Passive IR (PIR): Only detector, no emitter. Detects IR radiation emitted by objects (human body ~9-10 µm). Used in motion detection, security.

    Resistive IR not standard term.

    Final Answer

    Passive IR → Option (ii).

  5. Q2a. What is a Tactile Sensor? How it Works? Write its Types, Advantages, Disadvantages & Applications.20247m

    Module 1: Sensor classifications and characteristics

    What is a Tactile Sensor? How it Works? Write its Types, Advantages, Disadvantages & Applications.

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    Answer

    1. What is a Tactile Sensor?

    Tactile sensor = artificial skin that detects contact—force, pressure, texture, slip, vibration—when robot touches object. Mimics human sense of touch. Output is electrical signal proportional to contact parameters.

    MermaidDiagram
    Rendering diagram…

    2. How It Works

    • Contact → Mechanical deformation of sensing element (elastomer, diaphragm, piezoelectric).
    • Transduction: Deformation → change in resistance / capacitance / charge / optical intensity.
    • Signal conditioning: Amplification, filtering, ADC → controller maps to force/pressure.

    Example (piezoresistive): R∝1/AR \propto 1/A, V=IRV = IR, pressure ↑ → RR ↓ → VV change.

    3. Types

    Type Principle Example
    Piezoresistive Resistance changes with pressure Conductive rubber, strain gauge
    Capacitive C=ϵA/dC=\epsilon A/d, dd changes Parallel plate with elastic dielectric
    Piezoelectric Charge on stress (Q=d33FQ=d_{33}F) PVDF, quartz
    Optical Light intensity/FTIR Fiber optic tactile
    Magnetic Hall effect Magnet + Hall sensor
    Resistive array Matrix of tactels Robot skin arrays

    4. Advantages

    • Object detection, grip force control, slip detection.
    • Lightweight, flexible (for dexterous hands).
    • High resolution arrays (10k tactels).
    • Non-vision contact sensing.

    5. Disadvantages

    • Wear, hysteresis, drift (piezoresistive).
    • Complex wiring for arrays.
    • Limited bandwidth (piezoelectric only dynamic).
    • Calibration needed, temperature sensitive.

    6. Applications

    • Robot gripping (force feedback for delicate objects).
    • Prosthetic hands / haptics.
    • Surface texture inspection, assembly (peg-in-hole).
    • Humanoid skin, slip detection for stable grasp.
    • Medical palpation, minimally invasive surgery.

    Final Answer

    Tactile sensor = contact force/pressure transducer; works via deformation → R/C/QR/C/Q change; types piezoresistive/capacitive/piezoelectric/optical; used for grip control, prosthetics, assembly with advantages of contact sensing but disadvantages of wear and calibration.

  6. Q2b. What is a Proximity Sensor? How it Works? Write its Types, Advantages, Disadvantages & Applications.20247m

    Module 1: Sensor classifications and characteristics

    What is a Proximity Sensor? How it Works? Write its Types, Advantages, Disadvantages & Applications.

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    Answer

    1. What is Proximity Sensor?

    Sensor that detects presence of nearby object without physical contact via field/radiation. Range typically 0–50 cm (IR, ultrasonic, inductive). Output binary (present/absent) or analog (distance).

    2. How It Works

    Object entering sensing field disturbs field → detector measures change → threshold → output.

    • Inductive: Oscillator coil → eddy currents in metal → amplitude drop → comparator.
    • Capacitive: Electrode capacitance C=ϵA/dC=\epsilon A/d → object changes ϵ\epsilon → frequency shift.
    • IR: IR LED emits, photodiode measures reflected intensity I∝1/d2I\propto1/d^2.
    • Ultrasonic: Emit chirp, measure time-of-flight d=c⋅TOF/2d=c\cdot TOF/2.
    MermaidDiagram
    Rendering diagram…

    3. Types

    Type Target Principle Range
    Inductive Metal Eddy current 1–10 mm
    Capacitive Any (dielectric) Capacitance 0–20 mm
    IR Reflective IR reflection 2–30 cm
    Ultrasonic Any TOF 2cm–4m
    ** Hall/Magnetic** Magnet Hall effect mm

    4. Advantages

    • Non-contact → no wear.
    • Fast response (ms).
    • Reliable in dirty environments (vs vision).
    • Simple interface (digital/analog).

    5. Disadvantages

    • Limited range.
    • Material dependence (inductive only metal, IR affected by color).
    • Ambient interference (light, sound, temperature).
    • Not precise distance (except ultrasonic).

    6. Applications

    • Robot obstacle avoidance, end-effector positioning.
    • Conveyor part detection, mobile robot navigation.
    • Security systems, touchless switches.
    • Assembly line counting.

    Final Answer

    Proximity = non-contact presence detector via electromagnetic/acoustic field disturbance; types inductive/capacitive/IR/ultrasonic; used for avoidance and detection with non-contact advantage but limited range/material dependence.

  7. Q9c. Write short note on: Interaction sensors20247m

    Module 1: Sensor classifications and characteristics

    Write short note on: Interaction sensors

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    Interaction Sensors

    Definition: Sensors detecting interaction between robot and environment/human (contact, force, proximity, touch, intention).

    Types:

    Type Measures
    Tactile Pressure/force, slip
    Force/Torque Fx,Fy,FzF_x,F_y,F_z, τ\tau
    Proximity (IR/ultrasonic) Nearby presence
    Physiological EMG, EEG for HRI
    Social Vision, sound for gesture

    Working: Transduction of interaction force/proximity → electrical.

    Applications: Collaborative robots (safety), haptics, handshake detection, assembly (force control).

    Advantages: Enables safe human-robot collaboration.

    Disadvantages: Fusion complexity, calibration.

    Final: Interaction sensors = tactile/force/proximity/physiological for HRI, enabling compliant interaction.

Next moduleModule 2: Position and velocity measurment