Real-Time Speed Control of a DC Motor using Open Source Code

Real-Time Speed Control of a DC Motor using Open Source Code
International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-2, Issue-6, January, 2013
Real-Time Speed Control of a DC Motor using
Open Source Code Tools
Ujjwal Mondal, Parthasarathi Satvaya, Sourav Kumar Das
Abstract— The presented work envisaged to explore the
possibility of developing ultra-low cost experimental setup for
teaching and learning Real-Time systems. The presented work
demonstrates, in steps, the development of a real-time control
system with free open source code softwares. The free suite utilized
and experimented within the present work composed by Linux
operating system and the Real Time Application Interface (RTAI)
add-on, the Scilab Computer Aided Control System Design
(CACSD) software and the Control & Measurement Device
Interface (COMEDI) drivers. Scilab/Scicos, a free scientific
software package for numerical computations and control system
simulation is used with RTAI to provide hard real-time extensions
in to Linux environment. The development and deployment
platform are the same and consisted of the (i) Linux, (ii) Scilab/
Scicos (iii) RTAI and (iv) COMEDI drivers running in a PC. The
investment is reduced to the hardware as well as in software cost,
which consists of a standard PC, dc motor and a COMEDI
compatible acquisition board. The most obvious advantage of the
proposed solution is that all the software or codes are free &
available in the web. The whole idea is demonstrated by real time
speed control of a dc motor using Pulse Width Modulation
(PWM).
Index Terms— RTAI, CACSD, COMEDI, SCILAB/ SCICOS,
PWM.
I. INTRODUCTION
Rapid Control Prototyping (RCP) requires two components
[1, 2] Viz. Computer Aided Control System Design (CACSD)
software and a dedicated hardware with a hard real-time
operating environment. Popular & widespread RCP
environments are based on the commercial software
Matlab/Simulink/Realtime-Workshop (RTW) - Real Time
Windows Target (RTWT) CACSD software or LABVIEW
which can be used to generate and compile codes for different
targets. The main disadvantage of this solution is the cost of
the software. The proposed solution overcomes the said
problem as it can be freely downloaded from the web.
Development system is based on Scilab/Scicos and Linux
RTAI, a hard real-time extension of the Linux operating
system [3]. This environment allows to quickly creating
real-time controllers for real plants by generating and
compiling the full control application directly from the Scicos
scheme.
A real time system must respond to a signal, event or
request fast enough to satisfy some time constraints with
extreme reliability.
In order to get a real-time eration a standard kernel must be
configured in a Linux base and before this configuration it
will include the patching of Hardware Abstraction Layer
Manuscript received on January, 2013.
Ujjwal Mondal, Department of Applied Electronics & Instrumentation
Engineering, RCC Institute of Information Technology, Kolkata, India.
Parthasarathi Satvaya, Department of Electrical Engineering, Haldia
Institute of Technology, Haldia, India.
Sourav Kumar Das, Department of Electrical Engineering, Haldia
Institute of Technology, Haldia, India.
(HAL) or Adaptive Domain Environment for Operating
Systems (ADEOS) with the kernel. After patching and
configuring the kernel (to make it real time compatible),
installation of the RTAI package must be carried out
including rtai-lab and comedi. After this whole process, a set
of kernel modules are created in the user specified directory
(“/usr/realtime”). Loading these modules, the real-time
functionality is obtained [4].
In this stage keeping the entire previous configuration we
should include COMEDI support over RTAI. The RTAI
package with rtai-lab and COMEDI can be access through
Scilab, when RTAI with COMEDI add-ons to Scilab and
loads COMEDI modules. Scilab/Scicos gives the GUI to
make RT simulation and as well as to generate codes and
executable for RT operation [5]. In our experiments a
COMEDI supported DAQ card is taken to set the RT target.
Running the created RT executable in a Linux terminal we can
observe the RT simulated signal through a CRO. Farther work
may be the generating of RT control signal for a small plant.
II. DEVELOPMENT SYSTEMS
A. Hardware
1. A P4 or equivalent processor
2. Minimum 512MB RAM
3. DC motor
4. Driver electronics circuit
5. Data Acquisition Card (DAQ)
B. Softwares or Codes
1. Operating
System:
Functional
GNU/Linux
environment, better with a Debian or a Debian-like
(e.g. Ubuntu) distribution.
2. A Kernel: it is necessary to ensure the best when the
kernel version of the Linux-OS is as close as possible
to the kernel we are going to compile and to merge
with the RTAI.
3. RTAI source code
4. Scilab source code
5. COMEDI and COMEDI-LIB source
Another two supporting source codes are required to
install. First one is “Mesa 3D” graphical library from and
second one is the “EFLTK” graphic widgets library. Some
software packages may have to upgrade and those are
Automake, autoconf bison (for comedi) cpp, ftgl-dev (for
efltk), gcc, g77, g++, gtk, libbind, libglu1-mesa-dev,
libglut-dev, libfltk, libgtk-dev, libdrm-dev, libncurses,
libperl-dev,mesa (related all packages),tcl8.4, tk8.4,
tcl-8.4-dev, tk8.4-dev, tcllib-1.9, x11-proto.
III. DEVELOPMENT PROCESS
A. Software development process in steps
1. Operating System: Functional GNU/Linux environment,
(experimented with Ubuntu 6.06)
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Real-Time Speed Control of a DC Motor using Open Source Code Tools
2.
Unpacking of kernel and RTAI source codes in the
directory “/usr/src” in the installed Linux. To ensure the
best performance, the kernel version we are going to
compile and to merge with the RTAI, should be as close
as possible to the kernel version of the Linux-OS.
3. Patching of the HAL or ADEOS over the kernel under
configuration.
4. Configuring the kernel for real time applications.
5. Compilation and Installation of the newly configured
kernel.
6. Updating of the boot loader to access newly installed
kernel.
7. Mesa and EFLTK installation
8. Installation of COMEDI and COMEDI-LIB
9. Configuration, compilation and Installation of RTAI.
10. Installation of Scilab & RTAI add-on to it [6].
11. Creating shared memory inodes for the activation of
RTAI and COMEDI.
12. Loading RTAI, COMEDI and DAQ modules.
B. Hardware development process
1) DC Motor Specifications
A dc motor is taken for real time experimentation purpose
with following details:
Model name: RF-500TB-12560
Voltage: Operating range: 6 volts to 12 volts.
Nominal=12 volts constant.
At No load:
Speed=5600 rpm.
Current=0.03 amp.
At maximum efficiency:
Speed=4653 rpm.
Current=0.11 amp.
Torque=18 g-cm.(1.76 mN-m)
Efficiency=67%
At stall:
Current=0.6A
Torque=12 g-cm(11.76 mN-m).
2) DC Motor Driver Electronics
As a digital driver of the dc motor model
RF-500TB-12560, we have taken L293D push-pull four
channel driver. A little modification is done in the input
section. For the safety of data acquisition card and PC,
Optocoupler PC817 is used in the input section to keep Data
Acquisition Card and dc motor driver circuitry optically
coupled or isolated from direct contact (Fig. 1).
3) Data Acquisition Card
A data acquisition card plugs directly into a personal
computer's bus. All the power required for the A/D converter
and associated interface components on the data acquisition
card is obtained directly from the PC bus. For the presented
work, RTAI with COMEDI provides a built-in graphical tools
and libraries for data acquisition and analysis. “Advantech
PCI-1711” data acquisition card is used which is a powerful
and multifunction cards for the PCI bus and supported by
COMEDI library.
IV. EXPERIMENTATION
A. Creating block diagram for Square wave generation
Open the TERMINAL and type “scilab”, it will open scilab
window and in the scilab window type „scicos‟ and it will
open untitled window shown in Fig. 2. Then open menu “edit”
and Select palettes. In the Palettes, select Sources at the top of
the pop-up window [7, 8]. This will open a window with a
group of source blocks as shown in Fig. 3. Take the red clock
on the Scicos diagram page. Open the RTAI-Lib palette in a
similar way as before and it will look like Fig. 4. From the
RTAI-Lib palette, take the “Square” block, “Scope” block &
“COMEDI D/A” block and place it in the main Scicos
window. Connect those blocks. After drawing the Block
diagram, we should make the “super block”. So we should go
to menu “Diagram” and select “Region to super block”. Cover
all the blocks excluding the Clock and dragging the mouse i.e.
we must draw an elastic frame around all the blocks as in Fig.
5 and it will make the required super block as shown in Fig. 6.
Double clicking on the super block we can again open those
basic blocks to set parameters as shown in Fig. 7.
Set parameters of Super-blocks:
Square block- “Val[0]/amplitude=1”, “Val[1]/time
period=1” and “Val[2]/On time=0.5”
& leave other parameter to default value.
Comedi block- Keep default value (channel 0)
Scope block- Keep default value.
Close the window and set clock parameter.
Clock: Set “Period =0.001” and “Init Time=0” Connect the
analog output (Channel 0) and analog ground of the signal
acquisition card to a real oscilloscope. For example: with the
“advantech PCI-1711” DAQ card, connect pins 58
(DAC0OUT) and 57 (AOGND).
Fig.2 Scicos Interface
Fig. 1 dc motor driver electronics
359
International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-2, Issue-6, January, 2013
Fig.6 RTAI Super block
Fig.3 Scicos Source Blocks
Fig.7 Inside of Super block
Fig.4 RTAI-Lib palette
B. Checkout of RT signal through X-rtailab and
Oscilloscope
Now going to the “RTAI” menu select “Set Target” and
click over super block. Now we have to compile using
“RTAI-Code gen” again through menu “RTAI”. If
compilation is properly done then on the scilab prompt a
group of information will come with the lat line “Created
Executable” as in Fig. 8.
Fig.5 Making of RTAI Super block
Fig.8 Compilation Information
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Real-Time Speed Control of a DC Motor using Open Source Code Tools
Let the new executable is renamed as “rt_square” and
saved in the current directory.
• In one terminal type: “rt_square –v” to run the executable
in Hard RTS mode with verbose output as in Fig. 9.
• In another terminal type: “xrtailab” to open a GUI &
from “File” menu select “Connect” and it will give the
option to set the target. Click on “OK” as shown in Fig.
10.
• A square wavelike wave form can be seen on the
Oscilloscope.
In xrtailab going to “View” select “parameters” and
“scope”. Now visualization parameters can be adjusted in the
“xrtailab” to see the square wave properly in to the
oscilloscope as shown in Fig. 11, 12.
Fig.11 Square wave in the scope of xrtailab
Fig.9 Running the Executable
Fig.12 Square wave in the Oscilloscope
C. Real-time speed control of dc motor using PWM
Pulse-width modulation (PWM) or duty-cycle variation
methods are commonly used in speed control of DC motors.
The duty cycle is defined as the percentage of digital „high‟ to
digital „low‟ plus digital „high‟ pulse-width during a PWM
period i.e. PWM the output voltage is the average of the
supplied voltage over ON/OFF time.
Fig.10 xrtailab Interface
Vav =Vs*D= (Ton*Vs)/(Ton+Toff)
When Vav=average voltage, D= duty cycle, Vs =Supply
Voltage, Ton=On time of the signal, Toff=Off time of the
Signal. Controlling the period (Ton+Toff) and on time (Ton) of
input pulses, the speed of the dc motor can be controlled as the
dc motor speed varies with the variation of the average
amplitude of input voltage to it. Steps to control the dc motor
are as follows:
Generate a real time square wave (Sec-IV).
Take that output signal from DAQ.
Fed that signal to the input section of a DC motor driver
(Sec. III).
Connect the DC motor driver output to the input of DC
motor (SEC. III).
361
International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-2, Issue-6, January, 2013
Change the parameters on the fly in “xrtailab” interface [7] Stephen L. Campbell, Jean-Philippe Chancelier, and Ramine
Nikoukhah. Modeling and Simulation in Scilab/Scicos. Springer,
(Fig. 11).
Berlin, Germany, 2006. URL www.scicos.org
Choose the “source” block parameter and set values as:
[8] Roberto Bucher and Silvano Balemi “Scilab/Scicos and Linux RTAI
–A unified approach” 2005 IEEE Conference on Control Applications
Val (0) = 1 (amplitude of pulses)
Toronto, Canada, August 28-31, 2005
Val (1) = 0.0009 (T on + Toff = Period of pulse)
Val (2) = 0.0002 (Ton)
Now varying Val (2) = 0.0002 to 0.0009 (Pulse Width
Ujjwal Mondal (b.1977) received his B.Tech. degree
Modulation) on the fly, speed of the motor can be changed. It
in Electronics & Instrumentation Engineering from
has been successfully experimented and variation in speed of
University of Kalyani, West Bengal, India, in 2005, the
the motor is observed. The dc motor with following details is
M.E. degree in Control Systems from Jadavpur
University, West Bengal, India, in 2008. His research
connected to the driving circuit.
interests include Real Time Systems, Electronic
Supply voltage to driver circuit= 5V.
Instrumentation; Wavelet based system analysis &
Voltage across motor=5 volts.
Repetitive Control. At present, He is an assistant
Current=0.03 amps
professor, Applied Electronics & Instrumentation
Engineering, RCC Institute of Information Technology, Kolkata, and West
Short circuit current=0.5 amps.
Bengal, India.
A set of results is tabulated in Table 1.
TABLE 1
Parthasarathi Satvaya (b.1985) received his B.Tech.
Sl.
Duty cycle
Voltage across Current through
degree in Electronics & Instrumentation Engineering
from Bankura Unnayani Institute of Engineering, West
No.
( %)
motor (V)
motor (A)
1
2
3
4
5
6
7
8
22.22
33.33
44.44
55.55
66.66
77.77
88.89
99.99
1.11
1.67
2.20
2.78
3.34
3.91
4.44
4.91
Bengal University of Technology, West Bengal, India, in
2006, the M.E. degree in Illumination Engineering from
Jadavpur University, West Bengal, India, in 2008. His
research interests include Smart Lighting, Real Time
Systems, Electronic Instrumentation. At present, He is an Assistant
Professor, Department of Electrical Engineering, Haldia Institute
Technology, Haldia, and West Bengal, India.
0.007
0.010
0.014
0.017
0.021
0.025
0.028
0.031
Table 1: Parameters reading during RT control of dc motor
V. CONCLUSIONS
Successful implementation of the real-time system
development and deployment were demonstrated by Speed
Control of a DC Motor using Pulse Width Modulation.
The advantage of the proposed solution is that all the
softwares are freely available on the web. However, unlike the
(costly) commercial packages, the information available
about these free softwares is scanty or sometimes confusing.
The contribution of this work is the attempt to remove some
of the difficulties by tracing through the development steps
and pitfalls.
In conclusion, this paper shows that with some adjustments
and moderate additional effort, control system designing tools
Scilab/Scicos and RTAI with COMEDI can successfully
replace the costly commercial alternatives for teaching and
learning Real Time Systems.
Sourav Kumar Das (b.1984) received his B.Tech.
degree in Electronics & Communication Engineering
from Dumkal Institute of Engineering & Technology
under West Bengal University of Technology, West
Bengal, India, in 2006, the M.E. degree in Control
Systems from Bengal Engineering & Science
University, Shibpur, West Bengal, India, in 2009. His
research interests include Real Time Systems, Power
Electronics, DSP & Advanced Control Systems. At
present, He is an assistant professor, Electrical Engineering, Haldia Institute
Technology, Haldia, and West Bengal, India.
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[1]
[2]
[3]
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[5]
[6]
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http://www.scilabsoft.inria.fr/doc/scicos/scicos.htm
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