T.C. DOKUZ EYLÜL UNIVERSITY ENGINEERING FACULTY ELECTRICAL & ELECTRONICS ENGINEERING DEPARTMENT MOBILE ROBOT LOCALIZATION with POSITION CONTROL Project Report by Ayhan ŞAVKLIYILDIZ - 2011502093 Burcu YELİS - 2010502069 Advisor Yrd.Doç.Dr. Ahmet ÖZKURT May,2015 IZMIR
ABSTRACT The subject of this project is the motion control problem of wheeled mobile robots. With reference to the unicycle kinematics, we review and compare several control strategies for trajectory tracking and pose stabilization in an environment free of obstacles. Project is developed for a two-wheel differentially-driven mobile robot. I
Contents ABSTRACT Contents List of Tables List of Figures I II III IV 1 INTRODUCTION 1 2 THE GOAL AND METHOD 2 2.1 Arduino.................................... 2 2.2 Reasons of Using Arduino.......................... 2 2.3 Hardware Components............................ 3 2.3.1 Arduino Mega 2560......................... 3 2.3.2 L298N Dual H- Bridge Motor Control.............. 4 2.3.3 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder.. 6 3 Algorithm 8 4 COST ANALYSIS 13 5 CONCLUSION 14 II
List of Tables 4.1 Cost Table.................................. 13 III
List of Figures 2.1 L298N Dual H- Bridge Motor Control.................. 4 2.2 Arduino Sketch Considerations....................... 6 2.3 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder....... 7 3.1 doencoder() Function Algorithm...................... 8 3.2 Mathematical expression for Pose of the Robot.............. 8 3.3 dopose() Function Algorithm........................ 9 3.4 doforward() Function Algorithm...................... 9 IV
1. INTRODUCTION Wheeled mobile robots are increasingly present in industrial and service robotics, particularly when flexible motion capabilities are required on reasonably smooth grounds and surfaces. Several mobility configurations (wheel number and type, their location and actuation, single- or multi-body vehicle structure) can be found in the applications. The most common for single-body robots are differential drive and synchro drive (both kinematically equivalent to a unicycle), tricycle or car-like drive, and omnidirectional steering. Beyond the relevance in applications, the problem of autonomous motion planning and control of robots have some theoretical challenges. In particular, these systems are a typical example of nonholonomic mechanisms due to the perfect rolling constraints on the wheel motion. In the absence of workspace obstacles, the basic motion tasks assigned to a wheel mobile robot may be reduced to moving between two robot postures and following a given trajectory. The robot position control indicates that the problem is truly nonlinear; linear control is ineffective, even locally. So the aim of this project is to provide robot position control in a theoretical approaches that reduce the errors. 1
2. THE GOAL AND METHOD The goal of this project is designing a low-cost robot which has position control. In this project, a robot which already exists in the school, was used. The goal is to: Research and choose small size and good features of hardware parts. Implement the system as fast as possible with cheap parts. Write the algorithm with minimax principle. In this project, Arduino program was used for software implementation. 2.1 Arduino Arduino is an open-source physical computing platform based on a simple microcontroller board, and a development for uploading software for the board. Position control,pose setting and motor controller algorithm will be programmed on Arduino. 2.2 Reasons of Using Arduino Arduino boards are inexpensive. The Arduino software runs on Windows, Macintosh OSX and Linux operating system. A great majority of microcontroller systems are limited to Windows. The Arduino programming is easy-to-use. The Arduino software has open source tools and can be expanded. The Arduino hardware can be expanded. 2
2.3 Hardware Components 2.3.1 Arduino Mega 2560 Arduino is a very popular and easy to use programmable board for creating your own projects. Consisting of a simple hardware platform and a free source code editor with an easy one-click compile/upload feature, it s designed to be really easy to use without being an expert programmer. Arduino is also the most popular microcontroller board for advanced users and all kinds of more ambitious projects. It s been used to make robots, home automation gadgets, automotive projects, for sensing and controlling lights, motors, locks and servos, sound and video, interactive objects like animated sculptures, toys and games, radio links and just about anything else you can dream up. It can even be a web server and connect your projects to the Internet. A huge number of example projects (including both hardware designs and software source code) are available to help beginners get started. 3
2.3.2 L298N Dual H- Bridge Motor Control An H-Bridge is a circuit that can drive a current in either polarity and be controlled by Pulse Width Modulation (PWM). Pulse Width Modulation is a means in controlling the duration of an electronic pulse. In motors try to imagine the brush as a water wheel and electrons as a the flowing droplets of water. The voltage would be the water flowing over the wheel at a constant rate, the more water flowing the higher the voltage. Motors are rated at certain voltages and can be damaged if the voltage is applied to heavily or if it is dropped quickly to slow the motor down. Thus PWM. Take the water wheel analogy and think of the water hitting it in pulses but at a constant flow. The longer the pulses the faster the wheel will turn, the shorter the pulses, the slower the water wheel will turn. Motors will last much longer and be more reliable if controlled through PWM. Figure 2.1: L298N Dual H- Bridge Motor Control 4
Pins: Out 1: Motor A lead out Out 2: Motor A lead out Out 3: Motor B lead out Out 4: Mo (Can actually be from 5v-35v, just marked as 12v) GND: Ground 5v: 5v input (unnecessary if your power source is 7v-35v, if the power source is 7v-35v then it can act as a 5v out) EnA: Enables PWM signal for Motor A (Please see the Arduino Sketch Considerations section) In1: Enable Motor A In2: Enable Motor A In3: Enable Motor B In4: Enable Motor B EnB: Enables PWM signal for Motor B Specifications: Double H bridge Drive Chip: L298N Logical voltage: 5V Drive voltage: 5V-35V Logical current: 0-36mA Drive current: 2A (MAX single bridge) Max power: 25W Dimensions: 43 x 43 x 26mm Weight: 26g 5
Figure 2.2: Arduino Sketch Considerations 2.3.3 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder This powerful is a brushed DC gearmotor that have hardware features an integrated quadrature encoder with 64 counts per revolution (CPR) of the motor shaft. DC motors are intended for use at 12 V, though in general, these kinds of motors can run at voltages above and below the nominal voltage (they can begin rotating at voltages as low as 1 V). Lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor. Using the Encoder A two-channel Hall effect encoder is used to sense the rotation of a magnetic disk on a rear protrusion of the motor shaft. The quadrature encoder provides a resolution of 64 counts per revolution of the motor shaft when counting both edges of both channels. To compute the counts per revolution of the gearbox output, multiply the gear ratio by 64. The motor/encoder has six color-coded, 11 (28 cm) leads terminated by a 1*6 female header with a 0.1 pitch. This header works with standard 0.1 male headers and our male jumper and precrimped wires. If this header is not convenient for your application, you can pull the crimped wires out of the header or cut the header off. The following table describes the wire functions: 6
Figure 2.3: 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder Cable Color and Names: Red : motor (connects to one motor terminal) Black : motor (connects to the other motor terminal) Green: encoder GND Blue : encoder Vcc (3.5 20V) Yellow : encoder A output White : encoder B output The Hall sensor requires an input voltage, Vcc, between 3.5 and 20 V and draws a maximum of 10 ma. The A and B outputs are square waves from 0 V to Vcc approximately 90 degree out of phase. The frequency of the transitions tells you the speed of the motor, and the order of the transitions tells you the direction. 7
3. Algorithm In this project, whole algorithm was written by us. Firstly, encoder output has been tested. Because encoder CPR(counter per revolute) values did not fit to encoder datasheet values. Hence, according to these measured counter values doencoder() function was constructed. After doencoder() function construction, interrupts were attached to the digital pins(2 and 3) of the Arduino Mega and interrupts were written in the initialization of the program. The encoder algorithm was shown in below figure: Figure 3.1: doencoder() Function Algorithm Secondly dopose() and doforward() function was constructed according to desired coordinate points by using the mathematical expression below: Figure 3.2: Mathematical expression for Pose of the Robot 8
Pose function was shown in below figure: Figure 3.3: dopose() Function Algorithm Forward function was shown in below figure: Figure 3.4: doforward() Function Algorithm 9
The main program is given below figure: 10
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4. COST ANALYSIS Product Quantity Unit Price Total Price; Arduino Mega 1 70 TL 70 TL; Motor Driver L298N 1 20 TL 20 TL; DC Brushed Motor with Encoder 2 80 TL 160 TL ; Other Materials - - 20 TL ; Total - - 270 TL; Table 4.1: Cost Table 13
5. CONCLUSION Every project progresses in the direction of theory. But the theoretical procedure might change with economical and environmental reasons. In order not to run into a problem, theoretical procedure has to be prepared with regard to economical and environmental reasons. In this paper, the road map has been explained as a process of the project. The software part of the robot has been researched and explained. Pose function, forward function,mathematical expressions, encoder function have been mentioned. Arduino has been mentioned related to the software part which based on Arduino microcontroller. The challenging part of this project is to reading the encoder counts, mathematical expressions and wheel errors. In this point, hardware implementation calculations should be sensitive for the main program was written in a good looped algorithm. 14