THEORY EXAMINATION (SEM–VI) 2016-17 MECHATRONICS

MECHATRONICS (EEN021)

SECTION – A

(Attempt All | 10 × 2 = 20 Marks)

(a) Sensor vs Transducer

Sensor: Detects a physical quantity (temperature, pressure, displacement).
Example: Thermistor

Transducer: Converts one form of energy into another (usually physical → electrical).
Example: LVDT

(b) Principle of Eddy Current Sensors

They work on electromagnetic induction. When a conductive target enters the magnetic field of a coil, eddy currents are induced, changing coil impedance. This change is used to measure displacement or proximity.

(c) Need for Signal Conditioning

Signal conditioning is required to amplify, filter, isolate, and convert signals so that sensor outputs are compatible with controllers or DAQ systems and free from noise.

(d) Data Acquisition

Data acquisition (DAQ) is the process of collecting, sampling, and converting real-world signals into digital data for processing and analysis.

(e) Symbol of 4/2 DCV and 4/3 DCV

4/2 DCV: Four ports, two positions (forward/reverse flow)

4/3 DCV: Four ports, three positions (center position included)
(Symbols are drawn neatly in exam using standard hydraulic notation.)

(f) Use of Rack & Pinion in Mechanical Actuation

Rack and pinion converts rotary motion into linear motion and vice versa.
Applications: Steering systems, CNC machines, linear actuators.

(g) Serial vs Parallel Communication

Serial: Data sent bit-by-bit (USB, RS-232) – slower but less wiring

Parallel: Data sent simultaneously – faster but requires more wires

(h) Ladder Logic for AND & OR Gates

AND Logic:
Output ON only if both inputs are ON

OR Logic:
Output ON if any input is ON

Truth tables are written clearly in tabular form.

(i) Why Closed-Loop Controllers Are Preferred

Closed-loop controllers use feedback to reduce error, improve accuracy, reject disturbances, and provide better system stability and performance.

(j) Mathematical Model of Spring-Mass-Damper System

For mass m, damping c, stiffness k:

mx¨+cx˙+kx=F(t)m\ddot{x} + c\dot{x} + kx = F(t)mx¨+cx˙+kx=F(t)

This is the standard second-order differential equation.

 SECTION – B

(Attempt Any FIVE | 5 × 10 = 50 Marks)

(a) Encoder & Measurement of Velocity

An encoder converts mechanical motion into electrical pulses.

Incremental Encoder:

Produces pulses proportional to rotation

Velocity is measured by counting pulses per unit time

Velocity∝Number of pulsesTime\text{Velocity} \propto \frac{\text{Number of pulses}}{\text{Time}}Velocity∝TimeNumber of pulses​ 

(b) Data Acquisition System & Signal Conditioning

DAQ System Components:

Sensors                                        Signal conditioning unit

Multiplexer                                  ADC

Computer/Controller                   Filtering: removes noise
Amplification: increases signal level for accurate conversion

(c) Direction Control Valve vs Process Control Valve

Direction Control Valve (DCV): Controls direction of fluid flow

Process Control Valve: Controls process variables like pressure, flow, temperature

(d) Types of Pressure Control Valves

Pressure Relief Valve – limits maximum pressure

Pressure Reducing Valve – maintains reduced downstream pressure

Sequence Valve – ensures operation in sequence

Working explained with neat sketches.

(e) Torsional Spring-Mass-Damper System Equation

Jθ¨+cθ˙+kθ=T(t)J\ddot{\theta} + c\dot{\theta} + k\theta = T(t)Jθ¨+cθ˙+kθ=T(t)

where
J = moment of inertia
c = torsional damping
k = torsional stiffness

(f) Electric Drive System – Working & Applications

Components: Motor, power electronics, controller, sensors

Working: Electrical energy → mechanical motion with controlled speed/torque

Applications: Robotics, conveyors, CNC machines, elevators

(g) Architecture of Microcontroller

Main blocks:                                                   CPU

ROM / Flash                                                   RAM

I/O Ports                                                         Timers/Counters

ADC                                                                Serial interfaces

Used for real-time control in mechatronic systems.

(h) PLC Architecture & Ladder Logic for Start-Stop Motor

PLC Architecture:                                          CPU

Input module                                                  Output module

Power supply                                                  Programming device

Ladder Logic:

Start button (NO)                                            Stop button (NC)

Motor coil with seal-in contact                       Motor stays ON after start until stop is pressed.

SECTION – C

(Attempt Any TWO | 2 × 15 = 30 Marks)

Case Study: Automobile Engine Control

Modern automobiles use Electronic Engine Control Units (ECU).

Sensors:                                                        Oxygen sensor

Throttle position sensor                                Crankshaft position sensor

Temperature sensors

Functions:                                                    Fuel injection control

Ignition timing                                              Emission control

Improved fuel efficiency

The ECU processes sensor data and controls actuators like injectors and ignition coils for optimal performance.

Micromechanical Systems & Computer Printer Case Study

Micromechanical Systems (MEMS):
Miniaturized mechanical and electro-mechanical elements integrated on silicon.

Applications: Accelerometers, pressure sensors, inkjet printers.

Computer Printer Case Study:
MEMS nozzles eject ink droplets precisely using thermal or piezoelectric actuation, achieving high-resolution printing.

Operating Principle of NC Machine

NC (Numerical Control) Machine:
Machine tool controlled by numerical instructions.

Working Steps:

Program preparation

Input to controller

Signal processing

Motor actuation

Tool movement

Advantages:

High accuracy

Repeatability

Reduced human error

Suitable for mass production