Mr Manoj Rajale

UNIT –II

Block Diagram Representation

Syllabus

Open and Closed loop control system,

Identification of key elements of mechatronics systems and

represent into block diagram (Electro-Mechanical Systems),

Concept of transfer function,

Block diagram reduction principles,

Applications of mechatronics systems:- Household,

Automotive, Shop floor, Industrial.

What is a Control ??

Control means to make

an out put ON or OFF

by help of Controlling

Devices like simple

toggle switch to a

complex system with

components such as

relays, timers, and

switches.

Types of control

1) On-Off control,

2) Sequential control,

3) Feedback control, and

4) Motion control.

Example of manual control

Manual Control circuits use components that require

human interaction in order to operate.

AC

source

Toggle switch

Control circuits may require manual control, Automatic

control or Combination of both.

A controlled circuit

Example of manual control

AC

source

Toggle switch

Example of Automatic control

Automatic control circuits can operate themselves

without the need for human interaction.

Float Switch has been operated by a floating

arrangement Automatically.

AC

source

Float switch

Example of Automatic control

Automatic control circuits can operate themselves

without the need for human interaction.

Float Switch has been operated by a floating

arrangement Automatically.

AC

source

Float switch

Example of Automatic control

Automatic control circuits can operate themselves

without the need for human interaction.

Float Switch has been operated by a floating

arrangement Automatically.

AC

source

Float switch

Example of Automatic control

Automatic control circuits can operate themselves

without the need for human interaction.

Float Switch has been operated by a floating

arrangement Automatically.

AC

source

Float switch

ControlA Control system performs following functions-

1. For particular input the system output can be controlled to a

desired particular value.

2. To minimize the error between actual and desired output

Actual Response

Desired Response

Open Loop Control

Output is dependent on input but controlling action is

totally independent of the changes in output, is an Open

Loop Control System.

No feedback is used, so the controller must independently

determine what signal to send to the actuator.

InputControl

LawPlant Output

u

Plant = Mathematical model of Input Amplifier + Actuator + Physical System

Input = Reference / Desired Input or Set Point Input

Output = Measured Output

Control Law = Mathematical model of the Controller

Advantages and Dis-advantages of Open Loop Control

Advantages:

Simple in construction

Low cost

Convenient to implement when output is difficult to

measure

Disadvantages:

It is inaccurate

Unable to sense the environmental changes or

disturbances

Closed Loop Control

e = Error = Input – Output

u = Control Input

InputControl

LawPlant Output∑

+

_

e u

Controlling action is dependent on the changes in

output

Examples of Closed Loop Control

Examples of Automatic Closed Loop Control

Advantages:

Accurate, since the controller modifies and manipulates

the actuating signal such that the error in the system will

be zero.

Self-correcting

Senses the environmental changes, and disturbances in

the system.

Disadvantages:

Complicated to design

Costly

Instable, since due to feedback , system tries to correct

the error.

Advantages and Dis-advantages of Closed Loop Control

Eg:-Various elements for controlling the Room temperature.

Controlled variable - the room temperature

Reference value - the required room temperature

Comparison element - the person comparing the measured value with required temp.

Error signal - difference between measured and required temperatures

Correction unit - the switch on the fire

Process unit - the heating by the fire

Measuring device- a thermometer

Automobile

Open Loop System

Antenna will rotate clockwise and anticlockwise

depending on the output signal, negative or positive.

Antenna will stationary if the input signal is 0v.

When the antenna is approaching the desired angle or

position, the input signal must approach 0v.

It can be conclude that the control action is

independent of the output.

Close Loop System Example for antenna pointing system

Close Loop System

From diagram, if θ0= θi then V0 = Vi so the error signal

Ve = Vi – V0

= 0V ( the antenna will be stationary )

If the V0 not equal Vi ,Ve greater or less than 0V, the antenna will

rotate clockwise, anticlockwise depending on a polarity of Ve.

This means that the antenna will continue rotating until V0 = Vi .

In this example, the system automatically corrects the output when

the system is disturbed. This system is known as ‘automatic control

system’.

Difference between Open loop and Closed loop systemSr.No. Open loop system Closed loop system

1 Not using feedback Feedback using

2 Less accurate More accurate

3 Simple in construction Complicated in construction

4 Optimisation in control is not

possible

Optimisation in control is possible

5 Easy maintenance & cost is less Difficult to maintain & cost is more

6 System cannot compensate for

disturbance.

system can compensate for

disturbance.

7 Eg. CD deck, Digital thermometer,

toaster, fan.

Eg. Automatic water level, air

conditioning system, robot (arm).

Feedback and its effect

Feedback system is a system that maintains a

relationship between the output and some reference

input by comparing them and using the difference as a

means of control.

Feedback is used to reduce the error between reference

and the system output .

Feedback effect on performance characteristic:

Stability

Overall gain

Sensitivity

External disturbances

Transfer Function Models Transfer function: is a mathematical representation, in terms of

spatial or temporal frequency, of the relation between the input and

output of a linear time invariant system.

Why TF?

Because it is easier / better to assess some things using classical

techniques, such as gain and phase margin.

How to determine TF?

Derive the Governing Differential Equation

Take Laplace transform of output

Take Laplace transform of input

Transfer function = L (output) / L (input)

Advantages and features of TF-

1. Gives mathematical model of system components

2. LT converts time domain equation into simple

algebraic equation

3. TF obtained for a pair of i/p and o/p

4. Once TF is known o/p response for any type of

reference i/p can be calculated

5. TF helps in analyzing stability of system

Disadvantages of TF-

1. Does not provide any information about physical

structuring of system

2. Applicable to linear time invariant system

Block diagram components

Block Diagram: Feedback

sHsG

sG

sR

sY

sHsG

sG

sR

sY

1 TF loop Closed

1 TF loop Closed

Block Diagram Simplifications

1.Cascade (Series) Connection

2. Parallel Connection

3. Eliminating a feedback loop

4. Moving a pickoff/takeoff point behind a block/ right

5. Moving a pickoff point ahead of a block/left

6. Moving a summing point ahead of a block

7. Moving a summing point behind of a block

G G

G

8.Replacing summing points

9. Combining summing points

Applications of Mechatronic System

1. Household

i. Refrigerator

ii. Washing m/c

iii. Microwave

2. Automotive

i. Fuel injection system

ii. Power steering

iii. Air conditioner

3. Shop floor

i. Tool monitoring system

ii. Automated guided vehicle

iii. Conveyor system

iv. Bottle filing plant.

Sequential Control

1. Event based

2. Time based

Event based- Washing m/c

Washing m/c

PWD - Pulse width modulation- Control speed of motor in diff phases

Time based -Water heating system

Control function is Inexact

No fail safe features

Fuel Injection

POWER STEERING MECHANISM

POWER STEERING MECHANISM