2024 question paper

Robotics Sensors and Actuators

28 questions

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).
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).
Q1c. MARG sensor is abbreviated as: (i) Magnetic Angular Rate and Gravity (ii) Magnitude Angular Rate and Gravity (iii) Magnetic Angular Resistance Gravity (iv) None of the above20242m
Module 2: Position and velocity measurment
MARG sensor is abbreviated as:
(i) Magnetic Angular Rate and Gravity
(ii) Magnitude Angular Rate and Gravity
(iii) Magnetic Angular Resistance Gravity
(iv) None of the above

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Answer

Correct Option: (i) Magnetic Angular Rate and Gravity

Explanation

MARG = Magnetic, Angular Rate, and Gravity sensor.

Components:

M = Magnetometer (magnetic field, heading)

A = Angular Rate = Gyroscope (angular velocity)

R = Rate (redundant) - sometimes expanded as Magnetic

G = Gravity = Accelerometer (gravity vector)

MARG = 9-DOF IMU: 3-axis magnetometer + 3-axis gyro + 3-axis accelerometer. Used for orientation estimation (AHRS) via sensor fusion (complementary / Kalman).

Other expansions (Magnitude, Resistance) are incorrect.

Final Answer

Magnetic Angular Rate and Gravity → Option (i).
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.
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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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).
Q1f. Which of the following types of speed is measured by a tachometer encoder? (i) False pulse (ii) Single revolution in multiple track (iii) Forward and inverse direction (iv) Exact position of the motor shaft20242m
Module 2: Position and velocity measurment
Which of the following types of speed is measured by a tachometer encoder?
(i) False pulse
(ii) Single revolution in multiple track
(iii) Forward and inverse direction
(iv) Exact position of the motor shaft

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Answer

Correct Option: (iii) Forward and inverse direction (tachometer with quadrature measures bidirectional speed)

Explanation

Tachometer encoder (incremental / quadrature) measures rotational speed and direction.

Quadrature (A/B channels) 90° out of phase → via phase lead/lag determines forward vs reverse and counts pulses → speed $\omega = \Delta\text{pulses}/\Delta t$ .

False pulse: Noise, not speed type.

Single revolution in multiple track: Absolute encoder (Gray code), measures absolute angle, not tachometric speed.

Exact position: Position encoder, not tachometer.

Tachogenerator gives analog voltage ∝ speed, but quadrature encoder gives digital bidirectional speed.

Final Answer

Forward and inverse direction speed (bidirectional) → Option (iii).
Q1g. What will be the number of tracks for the resolution of 11.25 degrees for an encoder? (i) 4 (ii) 5 (iii) 6 (iv) 820242m
Module 2: Position and velocity measurment
What will be the number of tracks for the resolution of 11.25 degrees for an encoder?
(i) 4
(ii) 5
(iii) 6
(iv) 8

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Worked Solution
Answer

Correct Option: (ii) 5

Explanation

Encoder resolution: $\text{Resolution} = \frac{360°}{2^{n}}$ where $n$ = number of tracks (bits).

Given resolution $= 11.25°$ :

$2^{n} = \frac{360}{11.25} = 32$

$n = \log_2 32 = 5$

Final Answer

5 tracks → Option (ii) (32 positions).
Q1h. In which type of system does power transmission take place through compressed air? (i) Fluid power system (ii) Pneumatic system (iii) Hydraulic system (iv) Stepper motors20242m
Module 4: Robotic actuators
In which type of system does power transmission take place through compressed air?
(i) Fluid power system
(ii) Pneumatic system
(iii) Hydraulic system
(iv) Stepper motors

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Worked Solution
Answer

Correct Option: (ii) Pneumatic system (also (i) Fluid power system is broader)

Explanation

Pneumatic: Uses compressed air (pneuma = air) for power transmission. Clean, fast, low force.

Hydraulic: Uses pressurized liquid (oil).

Fluid power system: Umbrella term for both pneumatic + hydraulic. Pneumatic is the specific air-based subset.

Stepper motors: Electrical.

If exam expects broad category, (i) Fluid power is also true, but (ii) Pneumatic is precise for air.

Final Answer

Compressed air → Pneumatic → Option (ii) (fluid power is generic).
Q1i. A variable reluctance stepper motor is constructed of material with salient poles: (i) Paramagnetic (ii) Diamagnetic (iii) Ferromagnetic (iv) Non-magnetic20242m
Module 5: Introduction to motors
A variable reluctance stepper motor is constructed of material with salient poles:
(i) Paramagnetic
(ii) Diamagnetic
(iii) Ferromagnetic
(iv) Non-magnetic

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Worked Solution
Answer

Correct Option: (iii) Ferromagnetic

Explanation

Variable Reluctance (VR) stepper: Rotor and stator salient poles made of soft ferromagnetic material (e.g., silicon steel, soft iron) with high permeability.

Ferromagnetic: Strongly attracted to magnetic field, low reluctance → torque via reluctance variation.

Paramagnetic: Weakly attracted, insufficient.

Diamagnetic: Repelled.

Non-magnetic: No interaction.

Rotor has no windings or magnets; torque produced by tendency to minimize reluctance (align poles).

Final Answer

Ferromagnetic → Option (iii).
Q1j. A stepping motor is a _____ device. (i) Mechanical (ii) Electrical (iii) Analogue (iv) Incremental20242m
Module 5: Introduction to motors
A stepping motor is a _____ device.
(i) Mechanical
(ii) Electrical
(iii) Analogue
(iv) Incremental

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Worked Solution
Answer

Correct Option: (iv) Incremental

Explanation

Stepper motor moves in discrete angular steps (e.g., 1.8° per pulse) in response to digital pulses. It is incremental / digital device.

Each pulse → one step, position = count × step angle.

Open-loop position control without feedback.

Also electromechanical (electrical + mechanical), but “incremental” distinguishes it from continuous analog motors.

Final Answer

Incremental (digital) → Option (iv).
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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): $R \propto 1/A$ , $V = IR$ , pressure ↑ → $R$ ↓ → $V$ change.

3. Types

Type	Principle	Example
Piezoresistive	Resistance changes with pressure	Conductive rubber, strain gauge
Capacitive	$C=\epsilon A/d$ , $d$ changes	Parallel plate with elastic dielectric
Piezoelectric	Charge on stress ( $Q=d_{33}F$ )	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 → $R/C/Q$ change; types piezoresistive/capacitive/piezoelectric/optical; used for grip control, prosthetics, assembly with advantages of contact sensing but disadvantages of wear and calibration.

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 $C=\epsilon A/d$ → object changes $\epsilon$ → frequency shift.
IR: IR LED emits, photodiode measures reflected intensity $I\propto1/d^2$ .
Ultrasonic: Emit chirp, measure time-of-flight $d=c\cdot TOF/2$ .

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.

Q3a. What is an Optical encoder? How it Works? Write its Types, Advantages, Disadvantages & Applications.20247m
Module 2: Position and velocity measurment
What is an Optical encoder? How it Works? Write its Types, Advantages, Disadvantages & Applications.

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Answer

1. What is Optical Encoder?

Device that converts rotary/linear position to digital pulses via light interruption. Resolution $=360°/2^n$ where $n$ tracks.

2. How It Works

LED → Code disk (opaque/transparent sectors) → Photodetector. Rotation interrupts beam → pulses count = angle, quadrature phase → direction.

Incremental: Tracks A/B 90° shifted → pulses, index Z. Count pulses $\Delta N$ → angle $\theta = \Delta N \times$ resolution.

Absolute: $n$ concentric tracks Gray code → unique $n$ -bit word per position, no homing.

3. Types

Type Principle Output

Incremental (quadrature) Two tracks A/B Pulses + direction

Absolute $n$ -track Gray Absolute $n$ -bit code

Linear Strip scale Linear position

Rotary Disk Angle

4. Advantages

High resolution ( $0.1°$ ), accuracy.

Non-contact (no wear vs potentiometer).

Digital output directly to controller.

Fast response.

5. Disadvantages

Incremental loses position on power-off (needs homing).

Dust/light contamination sensitive.

Costlier than potentiometer for low resolution.

6. Applications

Robot joint feedback, servo motors.

CNC, 3D printer, conveyor positioning.

Mobile odometry.

Final Answer

Optical encoder = light-interruption position sensor; counts pulses (incremental) or reads Gray code (absolute); high-resolution non-contact feedback for robot joints/CNC, needs homing for incremental.
Q3b. What is an Accelerometer? How it Works? Write its Types, Advantages, Disadvantages & Applications.20247m
Module 2: Position and velocity measurment
What is an Accelerometer? How it Works? Write its Types, Advantages, Disadvantages & Applications.

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Answer

1. What is Accelerometer?

Sensor measuring linear acceleration (m/s²) including gravity, via inertia. Output = acceleration vector.

2. How It Works

Proof mass $m$ suspended by spring. Acceleration $a$ → force $F=ma$ displaces mass $x=F/k$ → displacement → transduction.

Capacitive MEMS: Movable plate between fixed plates, $C=\epsilon A/d$ , $d$ changes with $a$ .

Piezoresistive: Strain gauge on cantilever.

Piezoelectric: Charge on crystal.

3. Types

Type Principle Range

Capacitive MEMS $C$ change ±2g to ±16g

Piezoresistive $R$ change High-g shock

Piezoelectric $Q$ Vibration only

Thermal Convection Low-g

4. Advantages

Measures tilt (gravity component) + vibration.

Small MEMS, low power.

3-axis available.

5. Disadvantages

Measures $a+g$ → needs fusion to get orientation.

Drift, noise, temperature sensitive.

Cannot measure constant velocity.

6. Applications

IMU for robot/drone stabilization.

Tilt sensing, fall detection.

Vibration monitoring, impact detection.

Smartphone auto-rotate, step counting.

Final Answer

Accelerometer = proof-mass inertia sensor $F=ma$ → $C/R/Q$ change; types MEMS capacitive/piezoresistive; advantages tilt+vibration sensing, used in IMU and motion tracking.
Q4a. What Is a Strain Gauge Sensor and How Does It Work? Write its Advantages, Disadvantages & Applications.20247m
Module 3: Force and Torque measurment
What Is a Strain Gauge Sensor and How Does It Work? Write its Advantages, Disadvantages & Applications.

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Answer

1. What is Strain Gauge?

Resistive sensor measuring strain $\epsilon = \Delta L/L$ via resistance change. Bonded to structure, deforms with it.

2. How It Works

Resistance $R=\rho L/A$ . Strained → $L$ ↑, $A$ ↓ → $R$ changes: $\Delta R/R = G_F \cdot \epsilon$ , $G_F$ gauge factor (~2). Wheatstone bridge measures $\Delta R$ : $V_o = V_s \cdot (\Delta R/4R)$ for quarter bridge.

3. Advantages

High sensitivity for force/pressure/weight.

Small, cheap, static + dynamic.

Easy bridge interfacing.

4. Disadvantages

Temperature drift (needs compensation).

Small signal (mV) needs amplification.

Bonding sensitive, hysteresis.

Nonlinear for large strain.

5. Applications

Load cells, weighing scales.

Robot force sensing, torque measurement.

Structural health monitoring.

Pressure diaphragms.

Final Answer

Strain gauge = $\Delta R/R=G_F\epsilon$ via Wheatstone bridge; advantages high sensitivity for force, used in load cells/robot force, disadvantages temperature drift and small signal.
Q4b. What is a Ultrasonic sensor? How it Works? Types, Advantages, Disadvantages & Applications.20247m
Module 3: Force and Torque measurment
What is a Ultrasonic sensor? How it Works? Types, Advantages, Disadvantages & Applications.

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1. What is Ultrasonic Sensor?

Non-contact distance/proximity sensor using ultrasound (40kHz) time-of-flight.

2. How It Works

Transmitter emits chirp → reflects off object → receiver measures TOF $T$ , distance $d = c\cdot T/2$ , $c≈343$ m/s air.

3. Types

Type Principle

Transceiver (single) Same element TX/RX

Separate TX/RX Two elements

Analog Continuous $d$ voltage

Digital Threshold binary

4. Advantages

Works on any material/color, transparent.

Range 2cm–4m, low cost.

Not affected by light.

5. Disadvantages

Slow (sound speed), 40ms per measurement.

Beam spread (30°), poor for narrow.

Temperature affects $c$ , soft materials absorb.

Minimum dead zone ~2cm.

6. Applications

Robot obstacle avoidance, parking.

Level sensing (tank).

Medical imaging, non-destructive testing.

Final Answer

Ultrasonic = $d=cT/2$ TOF, types transceiver/separate, advantages material-independent range, used for robot navigation and level sensing but slow and beam-wide.
Q5a. Write Hydraulic actuators: operating principle, advantage and disadvantage.20247m
Module 4: Robotic actuators
Write Hydraulic actuators: operating principle, advantage and disadvantage.

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Hydraulic Actuator

Operating Principle: Pascal's law $P=F/A$ . Pressurized oil (50–300 bar) from pump → valve → cylinder/piston → linear/rotary motion. Force $F=P\cdot A$ , flow $Q=A\cdot v$ .

Components: Reservoir, pump, relief valve, directional control valve, cylinder, piston, filter.

Advantages

High force/power density (tons).

High stiffness, good for heavy loads.

Smooth, precise with servo valve.

Self-lubricating.

Disadvantages

Leakage, oil contamination, fire hazard.

Need power pack, bulky, noisy.

Slow response vs electric, temperature sensitive.

Maintenance high.

Applications

Excavator, press, industrial robot heavy payload.

Final Answer

Hydraulic = Pascal $F=PA$ via oil pressure, advantages high force, disadvantages leakage and bulk.

Type	Principle	Output
Incremental (quadrature)	Two tracks A/B	Pulses + direction
Absolute	$n$ -track Gray	Absolute $n$ -bit code
Linear	Strip scale	Linear position
Rotary	Disk	Angle

Type	Principle	Range
Capacitive MEMS	$C$ change	±2g to ±16g
Piezoresistive	$R$ change	High-g shock
Piezoelectric	$Q$	Vibration only
Thermal	Convection	Low-g

Type	Principle
Transceiver (single)	Same element TX/RX
Separate TX/RX	Two elements
Analog	Continuous $d$ voltage
Digital	Threshold binary

Q5b. Compare hydraulic, Pneumatics and Electric Actuator.20247m

Module 4: Robotic actuators

Compare hydraulic, Pneumatics and Electric Actuator.

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Comparison

Feature	Hydraulic	Pneumatic	Electric (Motor)
Medium	Oil 50–300 bar	Compressed air 5–10 bar	Current
Force	Very high (tons)	Low–medium	Medium (gearing)
Speed	Medium	Fast	Variable, precise
Stiffness	High	Low (compressible)	High with servo
Precision	High with servo	Low	Very high
Cleanliness	Leakage, messy	Clean	Clean
Cost/Maintenance	High (pump, filters)	Low	Medium
Power density	Highest	Low	Medium
Control	Servo valve	On/off, proportional	Servo driver

Advantages/Disadvantages Summary

Hydraulic: Heavy load, but leakage and bulk.
Pneumatic: Fast, cheap, clean, but low force and noisy.
Electric: Precise, clean, easy control, but limited force without gearbox.

Applications

Hydraulic: Excavator, press.
Pneumatic: Pick-place, gripper, door.
Electric: Robotic joints, CNC, drones.

Final Answer

Hydraulic high force, pneumatic fast cheap, electric precise clean; choose per load/speed/precision.

Q6a. What is a Torque sensor? How it Works? Types, Advantages, Disadvantages & Applications.20247m
Module 3: Force and Torque measurment
What is a Torque sensor? How it Works? Types, Advantages, Disadvantages & Applications.

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Answer

1. What is Torque Sensor?

Sensor measuring twisting moment $\tau = r \times F$ (Nm) on shaft.

2. How It Works

Twist angle $\theta = TL/(GJ)$ or strain on shaft. Transduction via strain gauges at 45° (max shear) on shaft, Wheatstone bridge measures $\Delta R$ .

Reaction: Static mount measures reaction torque.

Rotary: Slip rings/telemetry for rotating shaft.

3. Types

Type Principle

Strain gauge $\Delta R/R$ on shaft

Magnetoelastic Permeability change

SAW Frequency shift

Optical Twist angle via encoder

4. Advantages

Control joint effort, assembly.

Overload protection.

Small, high sensitivity.

5. Disadvantages

Temperature drift, needs calibration.

Slip ring wear for rotary.

Cross-sensitive to bending.

6. Applications

Robot joint torque control, grinding, screwing.

Automotive engine, steering.

Prosthetics.

Final Answer

Torque = strain on shaft at 45° via bridge; types strain gauge/magnetoelastic; used for robot joint control with high sensitivity but temperature drift.
Q6b. Define Servo motor and explain in brief any type of servo motor, also write its application, advantage and disadvantage.20247m
Module 5: Introduction to motors
Define Servo motor and explain in brief any type of servo motor, also write its application, advantage and disadvantage.

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Definition

Servo motor: Closed-loop actuator with motor + feedback sensor (encoder/pot) + driver that controls position/velocity precisely via error correction $e=\theta_{ref}-\theta_{actual}$ .

Types (explain one: DC Servo)

DC Servo: DC motor + encoder + PID controller. Input PWM/analog, encoder feedback, driver H-bridge controls direction/speed. Types: DC, AC, brushless.

Working: Controller compares desired vs actual via encoder → PID → H-bridge → motor rotates → encoder updates until error zero.

Applications

Robot joints, CNC, robotic arm, gimbal.

Conveyor, 3D printer.

Advantages

High precision, fast response, high torque with gear.

Closed-loop, no step loss (vs stepper).

Disadvantages

Costly, needs tuning (PID), complexity, requires feedback, hunting.

Final Answer

Servo = motor+feedback closed-loop; DC servo via encoder PID; advantages precision, disadvantages cost and tuning, used in robot joints/CNC.
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Q7a. Write and construct in detail of Variable Reluctance (VR) Stepper Motor, application, advantage and disadvantage.20247m
Module 5: Introduction to motors
Write and construct in detail of Variable Reluctance (VR) Stepper Motor, application, advantage and disadvantage.

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Answer

Variable Reluctance (VR) Stepper Motor

Construction: Stator 6 salient poles with windings (3 phases), rotor 4 soft-iron salient poles, no magnets/windings, air gap small. Ferromagnetic.

MermaidDiagram
Rendering diagram…
Working: Energize phase A → stator A poles become electromagnets → rotor minimizes reluctance aligns with A. Sequentially energize B, C → rotor steps 30° (360/(6*4/2)). Step angle $=360/(N_s \cdot N_r/(N_s-N_r))$ .

Advantages: Simple, cheap, no magnets, high speed, no detent.

Disadvantages: Low torque vs PM/hybrid, vibrations, low damping.

Applications: Low-cost positioning, printer carriage, clock.

Final: VR stepper soft-iron rotor steps by reluctance minimization, simple low torque.
Q7b. Write and construct in detail Series motors: Component, application, advantage and disadvantage.20247m
Module 5: Introduction to motors
Write and construct in detail Series motors: Component, application, advantage and disadvantage.

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Series Motor (DC Series)

Components: Field winding series with armature, commutator, brushes, stator/rotor iron.

Construction: Field coil in series → same current $I_a$ flows through field and armature. Flux $\phi \propto I_a$ , torque $T \propto \phi I_a \propto I_a^2$ .

Working: Supply → series field → armature → torque high at low speed, speed $N \propto V/\phi$ .

Advantages: Very high starting torque, suitable for traction.

Disadvantages: Speed dangerously high at no load, poor speed regulation, sparks.

Applications: Electric train, crane, hoist, starter motor.

Final: Series motor field series with armature $T\propto I_a^2$ , high starting torque for traction.
Q8a. Describe Belt transmission: Component, application, advantage and disadvantage.20247m
Module 6: Motion transmission
Describe Belt transmission: Component, application, advantage and disadvantage.

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Belt Transmission

Components: Driving pulley, driven pulley, belt (flat, V, timing) tensioned, idler.

Working: Friction (or teeth for timing) transmits motion. Velocity ratio $i = N_1/N_2 = D_2/D_1$ .

Advantages: Low cost, quiet, distance transmission, overload slip protects, damping.

Disadvantages: Slip/creep, limited power, tension maintenance, temperature sensitive, not precise.

Applications: Conveyor, robot wrist belt drive, 3D printer timing belt, fan.

Final: Belt pulley friction/timing transmission $i=D_2/D_1$ , cheap quiet but slip.
Q8b. Describe Gear transmission: Component, application, advantage and disadvantage.20247m
Module 6: Motion transmission
Describe Gear transmission: Component, application, advantage and disadvantage.

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Gear Transmission

Components: Pinion and gear (spur, helical, bevel, worm) meshing teeth on pitch circles. Velocity ratio $i=Z_2/Z_1$ , torque $T_2=T_1 i \eta$ .

Working: Teeth push, positive drive, no slip.

Advantages: High power, precise ratio, compact, high efficiency (95%), long life.

Disadvantages: Costly, noise, backlash, lubrication needed, fixed centers.

Applications: Robot gearbox, differential, CNC, automotive.

Final: Gear teeth positive drive $i=Z_2/Z_1$ , precise high power but noisy and backlash.
Q9a. Write short note on: Potentiometer20247m
Module 2: Position and velocity measurment
Write short note on: Potentiometer

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Potentiometer

Definition: Variable resistor with wiper, converts linear/angular position to voltage.

Construction: Resistive track (carbon/conductive plastic/wire) + wiper sliding, 3 terminals: two ends + wiper.

Working: Supply $V_{ref}$ across track, wiper voltage $V_o = V_{ref} \cdot (x/L)$ , $x$ position. Linear pot $V\propto x$ , rotary $V\propto\theta$ .

Advantages: Cheap, simple, absolute (no homing), low power.

Disadvantages: Contact wear, friction, limited resolution, noise, limited life, loading.

Applications: Robot joint position feedback (low-cost), joystick, volume control, calibration.

Final: Potentiometer $V_o=V_{ref}x/L$ cheap absolute position but wear.
Q9b. Write short note on: Gyroscopes20247m
Module 2: Position and velocity measurment
Write short note on: Gyroscopes

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Gyroscope

Definition: Sensor measuring angular velocity (°/s) and orientation via angular momentum.

Principle: Coriolis effect on vibrating mass: $F_c = -2m\omega \times v$ . MEMS tuning fork vibrates, rotation induces secondary vibration amplitude ∝ $\omega$ .

Types:

Type Principle

MEMS vibratory Coriolis on tuning fork

Optical (FOG) Sagnac interferometer

Mechanical Spinning rotor

Advantages: Measures angular rate, drift compensation with accelerometer (IMU).

Disadvantages: Drift integrates to angle error, temperature sensitive, cost for optical.

Applications: Drone stabilization, robot orientation, IMU, camera gimbal, navigation.

Final: Gyroscope Coriolis $\omega$ sensor, types MEMS/FOG, used for angular rate in IMU with drift.

Type	Principle
Strain gauge	$\Delta R/R$ on shaft
Magnetoelastic	Permeability change
SAW	Frequency shift
Optical	Twist angle via encoder

Type	Principle
MEMS vibratory	Coriolis on tuning fork
Optical (FOG)	Sagnac interferometer
Mechanical	Spinning rotor

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	$F_x,F_y,F_z$ , $\tau$
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.

Q9d. Write short note on: 2D and 3D velocity measurement20247m
Module 2: Position and velocity measurment
Write short note on: 2D and 3D velocity measurement

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2D and 3D Velocity Measurement

2D Velocity: Vector $\vec{v}=(v_x,v_y)$ in plane. Methods:

Wheel odometry: $v = \omega r$ , two wheels → $v_x, \omega_z$ .

Optical flow: Camera estimates $(u,v)$ pixel/frame → $v_{world}$ .

2D LIDAR Doppler: Frequency shift $\Delta f = 2v/\lambda$ .

IMU + GPS: Integrate $a_x,a_y$ .

3D Velocity: $\vec{v}=(v_x,v_y,v_z)$ .

3D optical flow / stereo vision: Depth $Z$ via disparity, $v_z = \Delta Z/\Delta t$ .

Doppler LIDAR / Radar: 3D $f_d$ .

IMU 6-DOF: Accelerometer + gyro fusion (Kalman) → $v_{3D}$ .

VIO: Visual-Inertial Odometry.

Comparison:

Feature 2D 3D

Sensors Encoders, 2D LIDAR, single camera Stereo camera, 3D LIDAR, IMU

Complexity Low High

Applications Mobile base, AGV Drone, manipulator

Final: 2D = planar $(v_x,v_y)$ via odometry/optical flow, 3D adds $v_z$ via stereo/Doppler/IMU fusion.

Feature	2D	3D
Sensors	Encoders, 2D LIDAR, single camera	Stereo camera, 3D LIDAR, IMU
Complexity	Low	High
Applications	Mobile base, AGV	Drone, manipulator

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Robotics Sensors and Actuators

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Pocketly on Android

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1. What is a Tactile Sensor?

2. How It Works

3. Types

4. Advantages

5. Disadvantages

6. Applications

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1. What is Proximity Sensor?

2. How It Works

3. Types

4. Advantages

5. Disadvantages

6. Applications

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1. What is Optical Encoder?

2. How It Works

3. Types

4. Advantages

5. Disadvantages

6. Applications

Final Answer

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1. What is Accelerometer?

2. How It Works

3. Types

4. Advantages

5. Disadvantages

6. Applications

Final Answer

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1. What is Strain Gauge?

2. How It Works

3. Advantages

4. Disadvantages

5. Applications

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1. What is Ultrasonic Sensor?

2. How It Works

3. Types

4. Advantages

5. Disadvantages

6. Applications

Final Answer

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