A Flexible Closed Loop PMDC Motor Speed Control System for Precise Positioning

Shakil Seeraji, Enaiyat Ghani Ovy, Tasnim Alam, Ahsan Zamee & Abdur Rahman Al Emon
International Journal of Robotics and Automation (IJRA), Volume (2) : Issue (3) : 2011 211
A Flexible Closed Loop PMDC Motor Speed Control System for
Precise Positioning
Shakil Seeraji shakil.ae@mist.edu.bd
Department of Aeronautical Engineering
Military Institute of Science and Technology
Mirpur Cantonment, Dhaka-1216, Bangladesh
Enaiyat Ghani Ovy enaiyat_ovy@yahoo.com
Department of Mechanical and Chemical Engineering
Islamic University of Technology
Board Bazar, Gazipur-1704, BANGLADESH
Tasnim Alam rim_mist@yahoo.com
Department of Electrical electronic and communication Engineering
Ahsan Zamee zamee_mist@yahoo.com
Abdur Rahman Al Emon emon1535@gmail.com
Abstract
The speed control of DC motor is very significant especially in applications where precision is of
great importance. Due to its ease of controllability the DC motor is used in many industrial
applications requiring variable speed and load characteristics. So the precise speed control of a
DC motor is very crucial in industry. In this case microcontrollers play a vital role for the flexible
control of DC motors. This current research work investigates the implementation of an
ATmega8L microcontroller for the speed control of DC motor fed by a DC chopper. The chopper
is driven by a high frequency PWM signal. Controlling the PWM duty cycle is equivalent to
controlling the motor terminal voltage, which in turn adjusts directly the motor speed. H-bridge
circuit is implemented for the bi-directional control of the motor. A prototype of permanent magnet
DC motor speed control system using the microcontroller is developed and tested.
Keywords: ATmega8L Microcontroller, DC Chopper, PWM, Tachogenerator, PMDC Motor, H-
Bridge.
1. INTRODUCTION
DC motor transforms electrical energy into mechanical energy. They are used to drive devices
such as fans, cars, door locks, seat adjust, mirror adjust, anti-lock braking system window lifts,
robot arms, hoists etc. So the speed control of a DC motor is essential in this present industrial
world. Many significant researches have been found regarding control techniques of the DC
motors.
From earlier research work, some techniques to control the DC motors are notable to be
mentioned. Refai [1] designed a PID controller which was based on MC68B00 microprocessor to

control the speed of a DC motor. PROME2
was used for program storage rather than RAM or
ROM to improve the flexibility and avoid memory corruption or power interrupt. Abdelhay and
Haque [2] applied a minimum-variance self-tuner to control the speed of a DC motor. By
implementing this method satisfactory motor response was found and set point and load
disturbances were sustained which was further compared with a PID controller. Microcontroller
has been introduced later to regulate the speed of the DC motor. Ume et al. [3] used Motorola
MC68HC11 microcontroller to control the speed of a permanent magnet DC motor.
From recent literature survey, the use of microcontroller for the control of DC motor has been
found in many research works. Now-a-days, microcontrollers are used in the industrial world to
control many types of equipments ranging from consumer to specialized devices. Chattopadhyay
et al. [4] designed a microcontroller based position control system where the actuator was
operated by the signal obtained from the PC (through key board). In this work, the position of the
motor was controlled by the microcontroller based PI controller with interactive display control
facilities. Adaptive fuzzy and neural speed controllers have been designed and implemented very
recently to control the speed of a DC motor [5-8]. In this present work, the design and
implementation of an ATmega8L microcontroller based controller to control a permanent magnet
DC motor with speed feedback through a techogenerator is discussed elaborately. The actuator
is regulated by a microcontroller based adjustable closed loop controller that controls the speed
of a DC motor by using PWM and DC chopper. The system is interfaced to a LCD display so that
the state of the system can be monitored by an operator. An H-bridge is implemented in the
circuit for controlling the rotation of the motor in clockwise as well as anti-clockwise direction
simultaneously. AVR studio4 software is used for programming and PonyProg is used for
downloading the program to the microcontroller through parallel port.
2. SYSTEM DESCRIPTION REPEATABILITY
The block diagram of microcontroller based closed loop speed control of DC motor is shown in
the figure 1. The motor to be controlled is fed by a DC source through a chopper. The
techogenerator senses the speed, which gives voltage as output. And this voltage is fed to the
microcontroller to drive the speed of the motor.
FIGURE 1: Block diagram of microcontroller based closed loop speed control of DC motor.
The output voltage of techogenerator is provided to the microcontroller and microcontroller
determines the output voltage of the chopper fed to the DC motor for desired speed.
3. Circuit Hardware and Software Operation
Circuit hardware and software portions are discussed in the following sections.
3.1 Circuit Schematic Diagram

FIGURE 2: Circuit for the speed control of DC motor.
The operation of the control circuit is described below by its different portion.
3.1.1 Pulse Width Modulator Module (PWMM)
PWMM is a very efficient way of providing intermediate amounts of electrical power between fully
on and fully off. A simple power switch with a typical power source provides full power only, when
switched on. PWM is a comparatively-recent technique, made practical by modern electronic
power switches. In this research work, timer/counter2 (8-bit) was used to generate PWM for
varying the speed of DC motor (12V). Phase correct mode was used here. It has 2 different
modes of operation. Non-inverted mode was selected for this work.
3.1.2 Chopper Circuit
A DC chopper is a dc-to-dc voltage converter. It is a static switching electrical appliance that in
one electrical conversion, changes an input fixed dc voltage to an adjustable dc output voltage
without inductive or capacitive intermediate energy storage. The name chopper is connected with
the fact that the output voltage is a ‘chopped up’ quasi-rectangular version of the input dc voltage.
For this research work, a Buck converter (step down chopper) was implemented.
A pulse with fixed frequency is generated by the microcontroller, which is fed to the base of
transistor (D400). Transistor acts here as a switch. The output voltage of the motor is dependent

on the amount of the on time of the transistor. The more time transistor remains on more the
voltage will produce. A Freewheeling diode (1n4001) is used for back e.m.f. protection given to
other portion of the circuit. Output voltage of the motor terminal can be shown by the equation
given below.
DVV inout ×=
Where
offon
on
TT
T
D
+
=
And VVin 12=
Using the equation and by measuring the voltage by multimeter the following values are obtained.
TABLE 1: Motor terminal voltages at various duty cycles.
3.1.3 Sensor Design
For speed sensing purpose, another motor is used. This motor is used here as a tachogenerator.
As it is known that for a DC motor voltage is directly proportional to the speed. The
tachogenerator is coupled with the motor. And a potentiometer is connected to the terminal of the
tachogenerator. Tachogenerator gives voltage drop across the potentiometer according to the
speed of the motor. If the motor runs at a low speed it gives a lower value. And when it runs at its
maximum speed it gives a larger amount of voltage. As it is known that speed can be regulated
by regulating the pulse width, so varying the duty cycle the speed can be regulated. Output
voltages at different duty cycles have been found by varying the duty cycle controller register
OCR (output compare register).

FIGURE 3: Duty cycle vs Output voltage.
FIGURE 4: Pulses at 20% and 50% duty cycle.
Now the voltage drop across the potentiometer is fed to ADC of the microcontroller. According to
the ADC value, microcontroller will take decision whether pulse width needs increment or
decrement.
3.1.4 Circuit Logic Development
As this present work is based on the speed controlling of a DC motor, so in this work the desired
goal is to achieve a system with constant speed at any load condition. That means the motor will
run at fixed speed at any load condition. As it is known that the speed of a DC motor can be
varied by PWM technique so according to the value of duty cycle the motor speed can be varied.
Now a question arises how it can be measured the variation of speed of the motor? To do this
another DC motor is used, which is coupled with the main motor. When the motor will run, it will
also make the second motor starts rotating. And the motor will act as a speed to voltage
transducer or tachogenerator. That means it will give an output voltage according to speed. By
measuring the output voltage drop of the tachogenerator the speed can be measured easily. It is
mentioned earlier in the paper that the desire is to maintain constant speed at any load condition
so initially PWM variation registers are set at a fixed value. As a result a fixed output voltage at
the tachogenerator end will be found. Speed of the motor does not remain same all the time
because of the various external forces like air or defect in the motor coupler. Though it does not
vary by huge value so the output voltage at the microcontroller is set not by a single value rather
it is set by giving a range. For bi-directional controlling of the motor, an H-bridge circuit is used. In
the H-bridge circuit four NPN transistors are used as switch to change or choose the direction of

current flows to the motor. Opto-coupler is used between the motor and microcontroller for
isolation.
Now if a load is applied on the motor, the speed of the motor will suddenly decrease. And with the
decrement of the speed output voltage will also decrease. This output voltage is fed to the ADC
input of the microcontroller by using a potentiometer. The output voltage of the tachogenerator is
scaled to 5V as the microcontroller ADC inputs are 5V supported. As earlier a range of voltages
are set for the fixed duty cycle, so when the new value of voltage will be sensed by the
microcontroller it will also sense the decrement of the speed by comparing two values. Now the
controller unit will tend to improve the speed of the system, so that the output voltage remains
same of the tachogenerator. To improve the system speed microcontroller now will start
increasing the value of PWM controller register i.e. output compare register (OCR) until the input
voltage of the ADC reaches the desired level of voltage. Now after reaching the desired level of
voltage, OCR will stop further increment. Now two more condition arises here, that what would
happen if the sudden load drops down to very low amount and what would happen if the load is
very huge that motor cannot run at its desired speed? When the load will drop down to a low
value, the speed of the motor will be very high. As a result output voltage will be also very high.
So again controller unit will sense output voltage and will compare with the desired level of
voltage. The PWM controller register i.e. OCR will do the reverse operation. Now the value OCR
will decrease until the output voltage reaches its desired level. And for the second condition if the
load amount is so high that motor cannot run at its desired speed, then OCR will start increasing
until reaches its maximum value. For 8 bit timer/counter the maximum value of OCR is 255. Even
if after reaching the maximum value, there remains no improvement of the speed, i.e. output
voltage does not matches the desired level then microcontroller will send a message
“OVERLOAD” using the LCD (16×2 line), so that the user can understand the condition and
hence reduce the load of the motor.
3.1.5 PCB (Printed Circuit Board) Design
A printed circuit board, or PCB, is used to mechanically support and electrically connect
electronic components using conductive pathways, tracks, or traces, etched from copper sheets
laminated onto a non-conductive substrate. ORCAD family release 9.2(layout plus) was used for
control circuit design. Designed PCB figure is given below.
FIGURE 5: PCB layout of the control circuit.

FIGURE 6: The physical setup of the research work.
FIGURE 7: Showing value of output voltage of techogenerator.

Figure 8: Showing “OVERLOAD” message.
4. OPERATIONAL FLOW CHART
FIGURE 9: Operational flow chart for DC motor speed controller.

5. CONCLUSION
An embedded system is designed and implemented in this work. Controlling a permanent magnet
DC motor with speed feedback through a techogenerator is successfully implemented using an
ATmega8L microcontroller. Microcontroller provides very less requirement of hardware. The
system is made user friendly so that anybody can operate the system without any trouble. LCD
display is used to show the condition of the system. After knowing the condition the amount of
load can be changed if necessary. Finally it can be concluded here that the system reliability is
higher where the PMDC motor can be regulated easily as well as the maintenance of the motor
can be also improved.
6. REFERENCES
[1] MK Refai, Microprocessor-based digital controller for DC motor speed control,
Microprocessors and Microsystems, Volume 10, Issue 10, December 1986, Pages 543-
552.
[2] Sofyan A Abdelhay, M Azharul-haque, DC-motor control using a minimum-variance self-
tuner, Microprocessing and Microprogramming, Volume 19, Issue 3, June 1987, Pages
227-231.
[3] Charles I. Ume, John Ward, Jay Amos, Application of MC68HC11 microcontroller for speed
control of a DC motor, Journal of Microcomputer Applications, Volume 15, Issue 4, October
1992, Pages 373-385.
[4] Subrata CHATTOPADHYAY, Utpal CHAKRABORTY, Arindam BHAKTA and Sagarika PAL,
Microcontroller Based Closed Loop PMDC Motor Position Control System, Sensors &
Transducers Journal, Vol. 102, Issue 3, March 2009, pp. 62-70.
[5] M. D. Minkova, D. Minkov, J. L. Rodgerson, R. G. Harley, Adaptive neural speed controller
of a dc motor, Electric Power Systems Research, Volume 47, Issue 2, 15 October 1998,
Pages 123-132.
[6] Gerasimos G. Rigatos, Adaptive fuzzy control of DC motors using state and output
feedback, Electric Power Systems Research, Volume 79, Issue 11, November 2009, Pages
1579-1592.
[7] Karim H. Youssef, Hasan A. Yousef, Omar A. Sebakhy, Manal A. Wahba, Adaptive fuzzy
APSO based inverse tracking-controller with an application to DC motors, Expert Systems
with Applications, Volume 36, Issue 2, Part 2, March 2009, Pages 3454-3458.
[8] Jui-Hong Horng, Neural adaptive tracking control of a DC motor, Information Sciences,
Volume 118, Issues 1-4, September 1999, Pages 1-13.

A Flexible Closed Loop PMDC Motor Speed Control System for Precise Positioning

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