MECHATRONICS SYSTEM DESIGN

(MTE-401) 2 hr Lecture on 15th Sep 2014

COURSE DETAILS

3 Credit hour theory = 3 hours teaching per week

Course Book

Mechatronics Electronic control systems in Mechanical and Electrical engineering (3rd Edition) by W. Bolton

Available in Mechatronics Library

Other useful books (For in depth study)

Mechatronics System Design (2nd Edition, SI) by Devdas Shetty and Richard A. Kolk

The Mechatronics Handbook by Robert H. Bishop

I will email soft copies to CRs.

Course website

www.mte401.weebly.com

All course-works will be submitted via website

All lecture notes will be available on course website

TODAYS LECTURE

Introduction to Mechatronics System Design

Real world examples

Mechatronics Design Approach

Sensors and transducers

Performance Terminology

INTRODUCTION TO MECHATRONICS

SYSTEM DESIGN

SYSTEMS

OPEN LOOP VS CLOSED LOOP SYSTEM

MECHATRONICS KEY ELEMENTS

WASHING MACHINE EXAMPLE

POINT AND SHOOT CAMERA EXAMPLE

MECHATRONICS DESIGN APPROACH

SENSORS AND TRANSDUCERS

A sensor is a device which produce a signal

relating to the quantity being measured.

A transducer is a device which experience a

related change when subjected to some physical

change.

The term sensor and transducers used

interchangeably.

Some measurement systems may use

transducers

PERFORMANCE TERMINOLOGY

Range and Span

The range of a transducer defines the limits between

which the input can vary

Span is difference between the maximum and

minimum value

A load cell can measure the force between 10kN-

100kN. Its range is 10kN to 100kN while its span is

90kN

Error

Error is the difference between the result of a

measurement and the true value of the quantity

being measured.

Error = measured value - true value

PERFORMANCE TERMINOLOGY

Accuracy

Accuracy is the extent to which the value indicated

by a measurement system might be wrong

It is the summation of all possible errors that are

likely to occur

For example, a temperature measurement system be

specified as having an accuracy of ±2°C

Accuracy is often expressed as percentage of full scale

reading (%FSR)

For example a sensor have an accuracy of ±5% of full

scale reading, with the range of 0 – 2000°C, then the

reading given can be expected to be within + or -10°C

of the true reading.

PERFORMANCE TERMINOLOGY

Sensitivity

Sensitivity is the relationship which relates a unit

change in output to a unit change in input.

For example a resistance thermometer may have a

sensitivity of 0.5Ω/°C

The term is often used to measure the sensitivity to

other inputs other than the one being measured. For

example a pressure sensor might have sensitivity to

temperature.

PERFORMANCE TERMINOLOGY

Hysteresis error

Different outputs from

a sensor for the same

input depending on

whether the value has

been reached by

continuous increase or

continuous decrease.

Defined as maximum

difference in output

for increasing and

decreasing value

PERFORMANCE TERMINOLOGY

Non-linearity error

A linear relationship assumed between the input and output of a transducer for its working range.

This assumption lead to non-linearity error

Different methods to find non-linearity error include End range value method

Best straight line for all values

Best straight line through zero point

PERFORMANCE TERMINOLOGY

Repeatability and Reproducibility

Defines as the ability of transducer to give the same

output for repeated application of the same input

value

The error arising from the non-repeatability is often

expressed as a percentage of full scale reading

Stability

It is the ability of a transducer to give same output

when used to measure a constant input over a period

of time.

The term drift is often used to describe the change in

output over the period of time.

PERFORMANCE TERMINOLOGY

Dead band/time

It’s a range of input values for which there is no output.

The dead time is a length of time from the application of an

input until the output begin to respond and changes.

Resolution

Resolution is the smallest change in the input value that

will produce an observable change in the output.

For example a wire-wound potentiometer might have a

resolution of 0.5 degree or as a percentage of full scale

reading.

For digital sensors a smallest change is 1 bit. Thus for a

sensor giving a data word of N bits, (a total of 2N) the

resolution is 1/2N

PERFORMANCE TERMINOLOGY

Output impedance

The output of a sensor needs to be connected with the

other systems

It is essential to know the output impedance of the

sensor so that impedance can be matched with the

interfacing circuit.

Non-matching of impedance can lead to a significant

change in the behaviour of overall system.