IRJET- FPGA based Controller Design for Mobile Robots

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FPGA based Controller Design for Mobile Robots
K. Anitha1, M. Srinivasa Rao2
1, 2Department of ECE, Prasad V Potluri Siddhartha Institute of Technology, Vijayawada, A.P, India
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Abstract:- Mobile robotics and embedded systems are two
research areas that have been receiving a considerable
attention in years. Combining these two research topics is
a very interesting and promising task. Some of the
problems of controlling robots using embedded systems
are designing device drivers, provide network
communication and develop complex control algorithms
under hardware limitations. This paper presents a
conception of mobile robots using rapid prototyping,
distributing the several control actions in growing levels of
complexity and computing proposal oriented to embed
systems implementation. This kind of controller can be
tested on different platform representing the mobile
robots using reprogrammable logic components (FPGA).
Different modules can be interfaced using FPGA controller.
Here we are constructing a simple robot model, which can
measure the distance from obstacle with the aid of sensor
and accordingly it is able to control the speed of motor.
Keywords — Infrared sensor, Obstacle Avoidance,
Motor driver L293D, Spartan3E FPGA, VHDL.
I. INTRODUCTION
The emergence of reconfigurable Field
Programmable Gate Arrays (FPGA) has given rise to a
new platform of complete mobile robot control system.
With FPGA devices, it is possible to tailor the design to fit
the requirements of applications (for example,
exploration and navigation functions for a robot).
General-purpose computers can provide acceptable
performance when tasks are not too complex. A single
processor system cannot guarantee real-time response
(particularly in the absence of considerable additional
hardware), if the environment is dynamic or semi-
dynamic. Here we focus on the design of the mobile
robot platform, with two driving wheels mounted on the
same axis. An FPGA-based robotic system can be
designed to handle tasks in parallel [3]. The mobile robot
consists of many units like Mechanics (chassis, housing,
wheels), electromechanical parts and Sensors.
Robots carry out various tasks. During these
tasks the robot moves and orients. While navigating, it
uses signals from the environment and the contents of
its own memory to make the correct decisions. This form
of navigation may be manifold depending on the given
task and problem [1].
Wheeled mobile robot:
Wheel control is less complex than the actuation
of multi-joint legs, and wheels cause minimal surface
damage in comparison with treads. Wheeled mobile
robots (WMRs) are more energy efficient than legged
robots on hard and smooth surfaces [6]. They require
fewer and simpler parts and are thus easier to build than
legged mobile robots.
A robot is capable of locomotion on surface
solely through the actuation of wheel assemblies
mounted on the robot and in contact with the surface.
Most designs require minimum two motors for driving
(and steering) a mobile robot. The combination of two
driven wheels allows the robot to be driven straight, in a
curve, or to turn on the spot.
II. HARDWARE DESCRIPTION OF MOBILE ROBOT
Architecture of Mobile Robot:
Within the proposal of mobile robotics
platform, the use of FPGA Controller, with control
software especially developed for the necessary
applications, is considered using structured libraries to
design, simulation, and verification with MODELSIM, we
convert the model to function prototyping using FPGA
hardware.
This system included both hardware and
software development. The output of ADC was
connected to the FPGA board and it was used as the
input of the source code. The assembly language that is
used in this system is VHDL. After the simulation and the
synthesis process, the program has been implemented
on the FPGA board.
The Spartan 3E family of Field-Programmable Gate
Arrays is specifically designed to meet the needs of high
volume, cost-sensitive consumer electronic applications
[4]. They are ideally suited to a wide range of consumer
electronics applications, including broadband access,
home networking, display/projection and digital
television equipment.
Fig.1: Block Diagram of mobile robot.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 05 Issue: 10 | Oct 2018 www.irjet.net p-ISSN: 2395-0072

FPGA’s avoid the high initial cost, the lengthy
development cycles, and the inherent inflexibility of
conventional ASICs. Also, FPGA programmability permits
design upgrades in the field with no hardware
replacement necessary, an impossibility with ASICs.
Logic Implementation on FPGA:
Basically two approaches are followed to implement
logic on FPGA board. They are Look up table approach
and Multiplexer approach.
In look up table approach, the logic is
implemented with LUTs. A LUT is basically a memory
device with certain capacity. As per the design
requirement, the LUT is filled up with specific value to
implement the design. The LUT approach is widely used
in most of the FPGAs.
As the logic capacity of FPGA increases, synthesis for
FPGAs is becoming more important. To efficiently exploit
increased logic capacity of FPGAs, synthesis tools and
efficient synthesis methods for FPGA targets become
necessary. One solution to designing large designs
efficiently is to use VHDL synthesis. Several synthesis
tools exist for mapping these descriptions to various
FPGA families.
FPGA implementation and programming:
Fig.2: Design flow on FPGA
To define the behavior of the FPGA, the user provides a
hardware description language (HDL) or a schematic
design. The HDL form is more suited to work with large
structures because it's possible to just specify them
numerically rather than having to draw every piece by
hand.
Once the design and validation process is
complete, the binary file generated is used to
(re)configure the FPGA. This file is transferred to the
FPGA/CPLD via a serial interface (JTAG).
In a typical design flow, an FPGA application
developer will simulate the design at multiple stages
throughout the design process. Initially the RTL
description in VHDL or Verilog is simulated by creating
test benches to simulate the system and observe results.
Then, after the synthesis engine has mapped the design
to a netlist, the netlist is translated to a gate level
description where simulation is repeated to confirm the
synthesis proceeded without errors.
Finally the design is laid out in the FPGA at which
point propagation delays can be added and the
simulation run again with these values back-annotated
onto the netlist.
III. IR DISTANCE MEASURABLE SENSOR
The Sharp GP2YOA21YK sensor shown in Figure is an
IR device that can provide distance measurements. This
sensor has a shorter range of 10 to 80cm (~ 4 to 32
inches). The measured distance appears as an analog
signal at the output.
Fig.3: Pin Assignment
Fig.4: Operation of Sharp IR Ranging Module
Fig.5: Internal Block Diagram of sensor.

As shown in Figure internally the GP2YOA21YK contains
an IR LED and a position-sensitive IR detector. The IR
LED transmits a modulated beam of infrared light.
When the light strikes an object, most of the light
will be reflected back to the LED. Since no surface is a
perfect optical reflector, scattering of the IR beam occurs
at the surface of the object and some of the light is
reflected back to the position sensitive detector.
By comparing the near and far object beams shown
in figure, it is apparent that position at which the
scattered reflected IR beam hits the detector is a
function of the reflection angle [7].
Characteristics:
Fig.6: Analog Output Voltage Vs Distance to Reflective
Object.
Alignment of sensor:
Fig.7: Proper Alignment of Moving Sensor.
IV. DRIVING DC MOTOR
A DC motor requires 9v power supply. The motor will
have two lines. Since we cannot connect a DC motor
directly to FPGA board, so we use a driver IC.
The driver IC takes the control from board and
converts the voltage level to level required to drive the
motor. Now the current for the motor is supplied by the IC
driver.
A program is written to drive the motor. It is assumed
that a switch is connected to digital pin2 and the function
of this switch is to change the motor state. Initially the
motor is OFF. The motor will run in one direction when the
switch is pressed.
L293D Driver IC:
Fig.8: L293D Driver IC.
The diagrammatic representation of L293D is as
shown below. L293D is a 16 pin DIP (dual in-line
package) IC.
Fig.9: Pin Assignment of L293D IC.
Pin 1 and Pin 9 are enable pins, EN1 and EN2
respectively. The basic purpose of enable pins is to
enable a particular channel. EN1 enables the first
channel while EN2 enables the second channel. If both
the channels are to be used simultaneously, then both
the enables pins, EN1 and EN2 should be enabled by
applying 5V power supply.
Suppose, to control the left motor which is connected to
Pin3 (Output1) and Pin6 (Output2). As mentioned above,
it requires three pins to control this motor - Pin1
(Enable1), Pin2 (Input1) and Pin7 (Input2). Here is the
truth table representing the functionality of this motor
driver.

Table 1: Truth Table for L293D Motor Driver IC
Pin 1 Pin 2 Pin 7 Function
High High Low Turn clockwise (Forward)
High Low High
Turn Anti-clockwise
(Reverse)
High High High Stop
High Low Low Stop
Low X X Stop
Table2: Logic inputs to activate the L293 chip
Functions Inputs (EN1 EN2 IN1 IN2 IN3 IN4)
Forward 111010
Reverse 110101
Left 110100
Right 110001
The motor driver can be mounted on the chassis
using the connectors as shown below:
Fig.10: Mounting of L293D
The ADC converter on the Spartan 3E board converts the
analog signal from sensor to digital signal which in turn
used to display the distance of the robot from obstacle
through seven segment and control the motor to drive in
a proper way.
V. SIMULATION RESULTS
i) Analog to digital converter
ii) Motor Control
iii). Display (seven segment)
iv) Controller
VI. CONCLUSION & FUTURE WORK
With the advancement in the field of robotics,
robots can be used in hazardous condition where the
presence of human is unsafe. Autonomous mobile robots
can also be used to deliver parts in factories, being
complementary platforms in a security system. This
paper describes the implementation of a FPGA based
controller for a simple mobile robot. This design may be
described as a mapping from the input sensors to the
actuators which control the robot motions. It is shown
that FPGA can be configured to implement the design
successfully. The wireless channel may also be added to
increase system flexibility.

VII. REFERENCES
[1] Prabhas Chongstitvatana. “A FPGA-based Behavioral
Control System for a Mobile Robot”. IEEE Asia-Pacific
Conference on Circuits and Systems, Chiangmai,
Thailand, 1998.
[2] Renato A. Krohling, Yuchao Zhou, Andy M. Tyrrell.
“Evolving FPGA-based Robot Controllers using an
Evolutionary Algorithm”. n International Conference
on Artificial Immune Systems, pp.41-46, 2002.
[3] Hannan Bin Aznar, MA, Dimond, K.R. “Design of an
FPGA based adaptive neural controller for intelligent
robot navigation”. In Proceedings of the Euromicro
Symposium on Digital Systems Design, pp.283-290,
2005.
[4] P.H.W. Leong and K.H. Tsoi “Field Programmable
Array Technology for Robotics Applications”. In IEEE
International Conference on Robotics and Bioimetics
ROBIO, 2005.
[5] P. Jin, M.H. Yang, L. Wei, R. Liu, Y.W. Cai, H.G. Liu, H.
Seitz, N. Butterfass, J. Hirzinger, G “High
performance DSP/FPGA controller for
implementation of HIT/DLR dexterous robot hand".
In International conference on Robotics and
Automation, ICRA, pp.3397-3402, 2004.
[6] J.M. Rosario, R. Pegoraro, H. Ferasoli. “Conception of
Wheeled Mobile Robots with Reconfigurable
Control using Integrate Prototyping”. Laboratory of
Automation and Robotics, Sao Paulo, Brazil
[7] István Matijevics: Microcontrollers, Actuators and
Sensors in Mobile Robots, in Proceedings of 4th
Serbian-Hungarian Joint Symposium on Intelligent
Systems (SISY206) September 29-30,
2006,Subotica, Serbia.
[8] Volnie A.Pedroni. “Circuit Design with VHDL”.MIT
Press, Cambridge, Massachusetts, London, England.
[9] Chris Lo. “Dynamic Reconfiguration Mechanism for
Robot Control Software”. Department of Electrical
and Computer Engineering, University of Auckland,
Auckland, New Zealand.

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