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Design and Implementation of Real Time

DC Motor Speed Control using Fuzzy Logic

Waleed Abd El-Meged El-Badry

Mechatronics Department

Faculty of Engineering, MUST

wbadry@must.edu.eg

3rd June, 2008

Abstract

In this paper, we try to implement a fuzzy logic controller (FLC) for DC motor

using Laptop, tower or industrial PC. The feedback is taken via tachometer

connected directly to motor of interest by coupling. Interfacing between PC and

DC Motor-Tachometer is done using NI USB 6008 and additional signal

conditioning circuitry. This system could assist students and novices to evaluate

rapidly Fuzzy Logic concepts and application using this low cost case study.

1. Introduction

Speed control of DC motors has been one of the crucial topics in Mechatronics

engineering, starting from simple Cartesian Robots, to giant industries such as

steel where maintaining motor speed of rollers affects drastically the shape of

rolled bars[1-2]. Due to non linearity of DC motors, designing control system

based on system identification is difficult and all system parameters are

approximated [2].

The heuristic knowledge based system, Fuzzy Logic proved to have the flexibility

of modelling nonlinear systems with fair or no knowledge of systems

identification. As the fuzzy logic core is based on “how people can do it”, many

legacy control systems are nowadays converted to be “fuzzy based systems” for

ease of maintenance and enhancement.

Fuzzy Logic Controllers can be practically implemented using several techniques,

using Microcontroller [3] where all fuzzy rules are placed by means of assembly

language, or a FL chip that is configurable using accompanying software, and

finally using PC where education mainly takes place in development process.

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2. Motivation

Several reasons were beyond selection of this implementation, these are

summarised below:

Development of Class Library can be utilised by students to develop fuzzy

logic systems easily with any .NET language (C#, VB, C++, Delphi and COBOL).

This would enable many students whose skills are in one or more of the

preceded languages rather than compulsory knowledge of MATLAB.

Implementing knowledge gained from “Fuzzy Logic” course tutored.

Studying the impact of fuzzy controller designed in real time environment.

3. Project Framework

DC motor speed control was inspired by an article entitled “Fuzzy Logic for Plain

Folks. Fig. 1 illustrates the proposed circuit connection [4].

Fig. 1 Proposed Circuit Connection

The proposed system can be summarised in the below block diagram

Fig.2 DC Motor Speed Control Block Diagram

Coupling

Computer

Fuzzification

Knowledge Base

Defuzzification Fuzzy Rules

D/A A/D M T

BJT Amplifier

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4. Project Setup

Two Identical DC motor were used to implement the project (one as DC motor and

the other works as tachometer), they are Toshiba 24V, 1.5A and Maximum of 180

RPM. Other parameters were obtained experimentally. The NI USB 6008 has built in

12 bits Analogue to Digital converter that can generate output voltage from 0- 5V

with maximum sourcing current of 150 mA. It also has a 0-10V, 12 bits Analogue to

Digital converter that were sufficient to measure the tachometer voltage directly.

Additional Circuit were used to accomplish two objectives, to start with, to amplify

the output analogue voltage generated from USB D/A from 0-5V into 0-12V, and

secondly, to supplement the DC Motor with current necessary that USB device can’t

afford. The figure shown illustrates how these problems were tackled by using

TIP41C NPN transistor with variable resistor for tuning [5]. Value of resistance were

evaluated experimentally

Fig. 3 Mapping 0-5V 150mA into

0-12V 2A Circuit

(Created Using Proteus VSM)

5. Experimental Work

Common-Emitter BJT amplifier described in preceded section has a nonlinear

relationship between Base Voltage (Vb) and Collector Voltage (Vc), the below chart

describes the relation between output USB analogue voltage (0-5V) from NI USB

6008 and Actual applied DC Motor voltage after amplification stage. The chart was

drawn by applying different voltages from USB Card and measuring the

corresponding applied voltage on DC motor simultaneously.

Q1TIP4143%

From USB 6008

+12V

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Fig. 3 Relationship between PC output voltage and Actual Applied Motor Voltage

Below 2V, “dead zone” is observed due coupling weight and friction, meanwhile,

saturation takes place after 4V.

Same procedure were followed to obtain chart depicts the DC Motor-

Tachometer Relationship. The below figure yields the experimental results:

Fig. 4 Motor-Tachometer Relationship

Data obtained experimentally from both charts were added to “the knowledge

base“was stored on software program to be utilised lately in implementation,

data between points were extracted using interpolation. Charts were generated

plotted using MATLAB.

6 7 8 9 10 11 12 133

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5

6

7

8

9

Applied Motor Voltage

Tach

om

ete

r C

orr

esp

on

din

g V

olt

ag

e

Experimental Data

Trend Line

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6. Fuzzy Variables and Rules

Two fuzzy variables were used based on knowledge base:

a- Input: Speed in (RPM) that maps current RPM and Desired RPM. Speed is

normalised.

Fig. 5 Input Membership Functions

b- Output: Output Voltage (V) for DC Motor. Voltage is normalised as well.

Fig. 6 Output Membership Functions

The first and last fuzzy terms holds greater range from the universe of discourse

for “fast response”, the other fuzzy terms were tuned by trial and error.

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Five fuzzy rules were used which maps each input linguistic value to and output

linguistic peer as follows

7. Results and Conclusion

The Fuzzy Logic Class Library was developed using Microsoft Visual Studio 2008. The

library can be used for implementation of both Mamdani and Takagi-Sugeno Fuzzy

Systems with both triangular and trapezoidal membership functions. A simple

software were created for testing purposes to compare results with another made

with MATLAB

Fig. 7 Same result yielded by both MATLAB and developed Class Library

Fuzzy Variables and rules for DC motor control were programmed using Visual Basic

2008.

If Speed is Very Slow then Speed Up Motor (1)

If Speed is Slow then Slightly Speed Up Motor (2)

If Speed is About Right then No Change Motor (3)

If Speed is Fast then Slightly Slow Down Motor (4)

If Speed is Very Fast then Slow Down Motor (5)

Same result were

obtained using MATLAB

and developed fuzzy logic

library by researcher

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Code Snippet 1 Formulation of Membership functions

Code Snippet 2 Formulation of Fuzzy Rules

The preceded code snippets were captured from the source code for case study;

researcher succeeded to obtain “user friendly” class library that is expected to be easily

comprehended by students.

A software were developed to control Motor Speed at 45 RPM, the below curve depicts

the fuzzy logic controller step input response.

Fig. 8 Screenshot from the developed software

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Fig. 9 Motor Response at Set Point 45 RPM

8. References

1- Thiang and Andru Hendra, “Remote Fuzzy Logic Control System For a DC Motor

Speed Control”, Jurnal Teknik Elektro Vol. 2, No. 1, Maret 2002: 8 – 12

2- Bogumila Mrozek and Zbigniew Mrozek, “Modelling and Fuzzy Control of DC

Drive”, 14-th European Simulation Multiconference ESM 2000, May 23-26,

Ghent, pp186-190

3- Yodyium Tipsuwan, “Fuzzy Logic Microcontroller Implementation for DC Motor Speed

Control” .

4- http://www.Fuzzy-Logic.com

5- Jan Axelson, “Parallel Port Complete”, 2nd Ed., Lakeview Research.