Design and Development of Digital PID Controller
for DC Motor Drive System Using Embedded
Platform for Mobile Robot
Chandra Shekhar Gohiya
S.S.Sadistap, S.A.Akbar, B.A.Botre
School of Electronics
Devi Ahilya University
Indore – 452017, India
csgohiya@gmail.com
Central Electronics Engineering Research Institute
Council of Scientific and Industrial Research
Pilani - 333031, India
1
ssadistap@yahoo.co.in, 2saakbar@gmail.com
This paper brings out a discrete PID control mechanism
for agriculture mobile robot. Here high speed ,high precision
DC motor control system has been designed in MATLAB
and implemented on ARM 9 based microcontroller .This
paper is organized in following ways .Section II concentrate
on overall system description. DC motor model derived for
the system is described in section III. Section IV describes
about PID controller model design while section V describe
the software development and Section VI shows the test
results observed and conclusion inferred from the project.
Abstract— In Agriculture industry, plants are prone to
diseases caused by pathogens and environment conditions and
it is a prime cause to lose of revenue. It requires continuous
monitoring of plants and environment parameters to overcome
this problem.
A mobile Robotic system for monitoring these parameters
using wireless network has been envisaged here and developed
based on ARM-Linux platform. Robotic platform consists of
ARM9 based S3C2440 processor from SAMSUNG and Linux
Kernel , Motor driver, robot mechanical assembly. The farm
environment and plant condition such as temperature,
humidity soil moisture content etc. are continuously monitored
through suitable data acquisition system incorporated in the
robotic system. A servo motor based robotic arm is designed
for collecting soil sample and test various soil parameters. A
closed loop feedback algorithm based on Digital PID controller
has been developed for precise position and speed control of
mobile robot.
II.
The Developed mobile robot system has embedded linux
platform comprises host PC using Ubuntu 10.04 and Target
device mini2440 an ARM architecture based development
board. Linux kernel 2.6.32 is cross-compiled using armlinux-gcc for ARM platform. Application programs are
developed for Target device and host using arm-qtopia and
x86 qtopia respectively. Developed mobile robot is depicted
in figure 1. All modules of robotic system is described
below.
The wireless control of mobile robot and monitored data
acquisition is accomplished using zigbee wireless protocol. For
displaying acquired data on host system a Graphical user
interface is designed using qt creater framework. For
independent functioning of mobile robot, application program
is written in c language and cross compiled using arm-linuxgcc compiler on Ubuntu 10.04 platform and ported on the
memory of ARM processor.
A. ARM Based Controller Unit
ARM9 based Samsung s3c2440 microcontroller is used
to control the various task .This provides a small size
microcontroller solution to the handheld device and ordinary
application of low price, low power consumption and high
performance. This 32 bit microcontroller has ARM920T
processor core integrated inside s3c2440A with maximum
master frequency of 400 MHz. This high end processor is
used to accomplish the task of on board image processing
using open-cv library in this mobile robot.
Keywords- ARM-Linux platform, PID controller, Zigbee.
I.
INTRODUCTION
Nowadays there are increasing awareness and
development of agriculture mobile robots around the world.
Mobile robots can be an effective tool to reduce the
production cost and manpower in agriculture. It can be used
for smart inspection of agriculture field. Several soil and
atmospheric parameters can be monitored wirelessly with the
help of mobile robots. Mobile robot driving system requires
high level of quickness, precision and accurate feedback
mechanism for speed and position control.
c
978-1-4673-4529-3/12/$31.00 2012
IEEE
SYSTEM DESCRIPTION
B. Power Module and Battery
7 Ah lead acid battery from nexrobotics is used to supply
the power to all module of the system . Power supply module
is designed for power requirement of 12V, 5V 3.3V and 1.8
V.
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C. Driver Module
For controlling the motor speed and direction a interface
circuit with L293D is used .Speed is controlled using PWM
signal generated by mini2440 .Driver module comprises 3
DC motor and 3 servo motor for various task of robot.
D. Sensor Module
Sensor module included imagining sensor (USBcamera), temperature sensor, humidity sensor, soil sensor
and IR sensor for obstacle detection. Optical Interrupter
switch is used as a motor speed decoder sensor.
E. Communication Module
Communicating wirelessly between host and target
xbee-pro zigbee wireless module from maxstream is used.
This is used to send commands to mobile robot and to
receive data from mobile robot .
Fig. 2. A schematic of DC motor
From Figure: 2 we can write the following equations
based on the Newton’s law combined with the Kirchoff’s
law:
(3)
(4)
Using the Laplace transform, equations (3) and (4) can be
written as:
(6)
where s denotes the Laplace operator. From (6) we can
express I(s):
(7)
(8)
Fig. 1. Complete System
III.
the transfer function from the input voltage, V (s), to the
output angle, θ, directly follows:
DC MOTOR MODEL
Direct-current (dc) motors are one of the most widely
used prime movers in the industry today. Advanced
manufacturing techniques have also produced dc motors with
ironless rotors that have very low inertia, thus achieving a
very high torque-to-inertia ratio. Low-time-constant
properties have opened new applications for dc motors in
computer peripheral equipment such as tape drives, printers,
disk drives, and word processors, as well as in the
automation and machine-tool industries [5]. The dc motor is
basically a torque transducer that converts electric energy
into mechanical energy. The motor torque T is related to the
armature current, i by a torque constant K;
T = Ki
(1)
The transfer function from the input voltage, V (s), to the
angular velocity, ω, is:
Armature
voltage
Vs
K / Ls + R
Torque
T(s)
1 / Js + b
Velocity
S
1/S
The generated voltage, Va, is relative to angular velocity
by;
Vs (s)
(2)
Back emf
K
Fig.3. Block diagram of DC Motor's Transfer function Mathematical
Model
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The Figure 3 shows mathematical model representation
of derived transfer function. In this project the permanentmagnet DC motor use is KM3448D. The parameters are:
R = 2.7 ohm , L = 0.004 H
b = 0.0000093 N-m-s-rad-1
k = 0.105 V-s-rad-1 (the back emf constant)
k = 0.105 N-m-A-1 (the torque constant)
J = 0.0001 kg-m2
Then transfer function for plant(dc motor) becomes
And the algorithm for the previous step in time is written
with the appropriate shift in subscript ,or
(11)
Subtraction of (11) from (10) yields
D(s) =
This is digitized using proper sampling time and digital
plant equation can be written as
D(z) =
Or combining like terms yields
(9)
(12)
IV.
PID CONTROL ALGORITHM
Figure 4 shows digital PID control system.
System transfer function can be given as
M(z) =
=
Which is the direct control algorithm. By taking the ztransform of the difference equation (12) we can determine
the companasator transfer function which will perform the
proportional plus integral plus derivative (PID) control
function :
Where
Fig. 4. Digital PID control system
The time domain relation for Continuous –time controller is
Associated transfer function for the controller can be given
by Laplace transform of equation
Where the choice of constant will determine the system
dynamics .Since this technique has proven so use full for
continuous time system .It is desirable to develop a digital
control algorithm for system. Digital control algorithm can
be derived by approximating the integral with trapezoidal
integration and derivative with backward difference
equation [7].
(10)
54
Using developed DC Motor model described in equation.
(9) and the closed loop system are used to determine PID
constants of digital PID controller using MATLAB. Derived
PID constants are Kp = 100; Ki = 200; Kd = 10. And using
these values the final control algorithm can be given by
equation Further this algorithm is used to calculate the error
signal compared to set point value and according to the
value of error, duty cycle of PWM signal is varied .
V.
SOFTWARE DEVELOPMENT AND IMPLEMENTATION
Actual Implementation of PID controller was done using
ARM based microcontroller (s3c2440) through an
interfacing circuit. For software part two software routine are
running in every 1/10th of a second, one is for calculating
speed and second one for generating control efforts .Flow
chart of control strategy is shown in figure 5. Programming
was done using c language. A constant signal varying from
50 % to 90 % duty cycle is applied from the microcontroller
amplified by interface circuit using L298.A wheel encoder
with N=8 index holes is connected to the shaft . In this
sensor a pair of IR LED and receiver is placed face to face in
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a fashion such that when an index hole comes in front of the
LED, output of the receiver goes low, otherwise output to
receiver is high . The microcontroller counts the number of
transition from high to low for a certain time interval and
calculates speed (in Hz) of the motor from the relation.
Speed = Time of counting * Number of Count / N.
Once the speed has been calculated, control efforts are made
to adjust the power delivered to motor.
This design is implemented on ARM9 based s3c2440
microcontroller. Proportional, integral and derivative
parameters are obtained for various load conditions to set the
speed.
Fig. 6. Stair step response with PID controller
Fig. 5. Control Strategy
Device-driver for timer :- PWM duty cycle is
controlled by a device driver program this device driver
program is customized as described below .
1. Setting GPB1 to TOUT1 i.e. pulse generating terminal.
2. Setting Timer Configuration Register 0 (TCFG0)
3. Setting Timer Configuration Register 1 (TCFG1).
4. Acquiring clock frequency of pclk from platform
clock queue of system through the function clk_get and
clk_get_rate defined in include /linux/clk.h
5. Interval is pclk/50/16/freq acquired in 4, setting the
value into timer count buffer register (TCNTB1).
6.For setting duty cycle such approach is adapted that
changes the value obtained in 5 into timer comparison buffer
register (TCMPB1)
7. Closing dead zone, automatic reloading, closing phase
inverter, renewing TCNTB1 and TCMPB 1 and starting
timer1 i.e. Timer control register (TCON).
8. Resetting TCON , clearing manual renew position of
timer 1.
VI.
RESULTS AND CONCLUSION
A real time Digital PID controller has been developed
and closed loop approach is adapted to control the speed of
the DC motor using embedded system . Character device
driver program is developed for DC motor control strategy.
Fig. 6 shows the close loop response of digital system.
Speed control with precision and high speed of operation is
important in robotic application. High precision control
implementation requirements have been met on ARM board
because it is 32-bit microcontroller; additionally it has all
necessary facility for concurrent programming and real-time
control for fast handling of events in Robotic applications.
ACKNOWLEDGMENT
The authors are thank full to Dr. Chandra Shekhar
Director CEERI for his encouragement and constant support.
The authors are also thank full to Head school of electronics
Indore for his help and support for the work.
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