Control of DC Servomotor Report submitted in partial fulfilment of the requirement to the degree of B.SC In Electrical and Electronic Engineering Under the supervision of Dr. Abdarahman Ali Karrar By Mohammed Sami Hassan Elhakim To Department of Electrical and Electronic Engineering University of Khartoum July 2008 Dedication I would like to take this opportunity to write these humble words that are unworthy of expressing my deepest gratitude for all those who made this possible. First of all I would like to thank god for my general existence and everything else around and within me. Second I would like to thank my beloved parents(Sami & Sawsan), my brothers (Tarig & Hassan), and my sister (Latifa), thank you so much for your support, guidance and care, you were always there to make me feel better and encourage me. I would like also to thanks all my friends inside and out Khartoum university, thank you for your patients tolerance and understanding, for your endless love that has stretched so far, for easing my pain and pulling me through. A special thanks to my partner Muzaab Hashiem without his help and advice i won’t be able to do what i did, thank you for being an ideal partner, friend and bother. Last but not the least i would like to thank my supervisor Dr. Karar and all those who helped me throughout this project, thank you for filling my mind with this rich knowledge. Mohammed Sami Hassan Elhakim. I Acknowledgement The first word goes to God the Almighty for bringing me to this world and guiding me as i reached this stage in my life and for making me live and see this work. To the principle of Khartoum university. To my supervisor Dr. Abdalrahman Ali Karrar who constructively criticize my work and in more ways than he will ever know and inspired me and I would like to thanks him for his interest, sincere encouragement and help throughout this project. I would like also to convey a special note of appreciation to the administration of Khartoum university and the staff of Electrical and Electronic Department, and to the staff of the computer labs for their continues assistance throughout this project. II Abstract A (Servomechanism), or servo is an automatic device that uses error-sensing feedback to correct the performance of a mechanism. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position or other parameters. Servomechanism is unique from other control systems because it controls a parameter by commanding the time-based derivative of that parameter. Servo systems are either electromechanical, electro hydraulic, hydraulic, or pneumatic. Whatever the form, a relatively weak signal that represents a desired movement of the load is generated, controlled, amplified, and fed to a servo motor that does the work of moving the heavy load. Servomechanisms were first used in military fire-control and marine navigation equipment. Today servomechanisms are widely used as in automatic machine tools, satellite-tracking antennas, remote control airplanes, automatic navigation systems on boats and planes, and antiaircraft-gun control systems. In this project we compared between several methods for controlling a dc servo motor.PWM (Pulse Width Modulation), PFM (Pulse Frequency Modulation) & linear method are used for controlling the speed of the motor. PCM (Pulse Code Modulation) is a method to control the position of the dc servo motor. The Micro-controller (atmega32) is the control commander used in this project and the results are monitored in Proteus simulation program. III المستخلص اﻵلية المؤازرة، او ما يعرف بالسيرفو عبارة عن جهاز تلقائى يستخدم دارة ارتجاع استشعار الخطأ لتصحيح أداء اﻵلية. ان هذا المصطلح ينطبق فقط على النظم التى بها دارة ارتجاع او اشارات لتصحيح الخطأ تساعد فى التحكم على الموقع الميكانيكى او اى قيم اخرى لﻻجهزة. اﻵلية المؤازرة فريدة عن غيرها من نظم التحكم ﻻنها تتحكم فى القيم المعينة عن طريق اصدار اوامر الى القاعدة الزمنية المشتقة من هذه القيمة. انظمة السيرفو اما نظم أجهزة الكهربائية اوهيروكهربائية ، اوالهيدروليكية ، أو ةهوائي. مهما كان شكلها فان اشارة ضعيفة نسبيا تمثل حركة الحمل المطلوبة يتم توليدها و التحكم فيها و تضخيمها ليغذى بها محرك السيرفو الذى يقوم بنقل الحمولة الثقيلة. آلية المؤازرة استخدمت ﻻول مرة ي الجيش للسيطرة على الحريق ومعدات المﻻحة البحرية . اما اليوم فان آلية المؤازرة تستخدم على نطاق واسع كما هو الحال في أدوات اﻵﻻت اﻷوتوماتيكية ، وتتبع اﻷقمار الصناعية والهوائيات ، وطائرات التحكم عن بعد ، ونظم المﻻحة التلقائية على القوارب والطائرات والمدافع المضادة للنظم المراقبة و غيرها. و في هذا المشروع نقوم بالمقارنة بين عدة وسائل للتحكم فى محركات السيرفو ذات التيار المباشر مثل PWM ) تعديل عرض النبضة( و PFM ) تعديل تردد النبضة( و اﻻنظمة الخطية، هذه الطرق الثﻻثة تستخدم للتحكم فى سرعة المحرك. و PCM ) تعديل رمز النبضة ( طريقة للتحكم فى موقع محركات السيرفو ذات التيار المباشر . )atmega32( هو المتحكم المستخدم فى هذا المشروع و تم رصد النتائج عن طريق برنامج محاكاة بروتوس. IV Table of contents Dedication I Acknowledgement II Abstract III IV المستخلص Table of content V List of figures VII List of tables VIII Chapter one: Introduction 1 1.1 Servos 1 1.2 Statement of the problem 1 1.3 Objectives 2 1.4 Methodology 2 1.4.1 PWM (Pulse Width Modulation) 2 1.4.2 PFM (Pulse Frequency Modulation) 2 1.4.3 PCM (Pulse Code Modulation) 2 1.5 Description of layout 3 Chapter Two: Literature review 4 2.1 Types of motors 4 2.1.1 AC motors 5 2.1.1.1 Induction motors 5 2.1.1.2 Synchronous motors 7 2.1.2 DC motors 8 2.1.2.1 Shunt wound motor 9 2.1.2.2 Series wound motor 10 2.1.2.3 Compound wound motors 11 2.1.2.4 Stepper motor 11 2.1.2.5 PMDC motor 12 2.2 System control 13 2.3 SERVOs 16 2.4 Types of feedback 18 2.4.1 Analog tachometer 18 2.4.2 Digital tachometer 19 2.4.2.1 Absolute encoder 19 2.4.2.2 Incremental encoder 20 2.4.2.3 Resolvers 21 2.5 Speed control for DC motors 23 2.5.1 Field current control 23 2.5.2 Armature control 23 2.6 Atmega32 micro-controller 24 2.7 ULN2003A amplifier 25 2.8 Control Methods 26 2.8.1 Linear method 26 2.8.2 PWM (Pulse Width Modulation) method 26 2.8.2.1 Normal mode 27 2.8.2.2 Fast PWM 28 V 2.8.2.3 Phase correct PWM 29 2.8.3 PFM (Pulse Frequency Modulation) 30 2.8.4 PCM (Pulse Code Modulation) 31 2.9 Switches 31 Chapter Three: Design and Implementation 32 3.1 System requirements 32 3.2 General system layout 32 3.3 system working mechanism 32 3.3.1 Linear method 32 3.3.2 PWM (Pulse Width Modulation) method 33 3.3.3 PFM (Pulse Frequency Modulation) method 34 3.3.4 PCM (Pulse Code Modulation) method 34 Chapter Four: Results and Test 36 4.1 Linear method 36 4.2 PWM (Pulse Width Modulation) method 36 4.3 PFM (Pulse Frequency Modulation) method 41 4.4 PCM (Pulse Code Modulation) method 41 Chapter Five: Conclusions and Comments 42 References 43 APPENDEX A Linear Method APPENDEX B PWM Method APPENDEX C PFM Method APPENDEX D PCM Method VI List of Figures Figure 2.1 Concept of electromagentism 4 Figure 2.2 Induction motor. 6 Figure 2.3 Cutaway of induction motor. 7 Figure 2.4 Cutaway of AC synchronous motor. 8 Figure 2.5 Typical speed-torque curve for shunt wound motors. 10 Figure 2.6 Typical speed-torque curve for series wound motors. 10 Figure 2.7 Typical speed-torque curve for compound wound motors. 11 Figure 2.8 Stepper motor. 12 Figure 2.9 Typical DC motor construction. 13 Figure 2.10 Open loop drive. 14 Figure 2.11 Example of an application using open loop drive. 14 Figure 2.12 closed loop drive. 15 Figure 2.13 The concept of SERVO system. 16 Figure 2.14 Tachometer. 19 Figure 2.15 Absolute encoder 20 Figure 2.16 Incremental encoder. 21 Figure 2.17 Rotating transformer. 22 Figure 2.18 Typical resolver output. 22 Figure 2.19 Atmega32 microcontroller 25 Figure 2.20 (ULN2003A) amplifier 25 Figure 2.21 PWM outputs. 27 Figure 2.22 Timing diagram for CTC. 28 Figure 2.23 Fast PWM Mode, Timing Diagram 29 Figure 2.24 Phase Correct PWM Mode, Timing Diagram. 30 Figure 2.25 Pulse Frequency Modulation. 31 Figure 3.1 Linear method. 33 Figure 3.2 PWM method. 33 Figure 3.3 PFM method. 34 Figure 3.4 PCM method 35 Figure 4.1 The PWM method generated wave for 10% duty cycle. 37 Figure 4.2 The PWM method generated wave for 30% duty cycle. 38 Figure 4.3 The PWM method generated wave for 50% duty cycle 39 Figure 4.4 The PWM method generated wave for 70% duty cycle. 40 Figure 4.5 The PWM method generated wave for 90% duty cycle. 40 VII List of Tables Table 4.1 Input value vs. Speed of linear method. 36 Table 4.2 Duty cycle vs. OCRO of PWM method. 36 Table 4.3 Period (ms) vs. Speed of PFM method. 41 Table 4.4 period (ms) vs. Angle of PCM method. 41 VIII [References] References [1] MODERN CONTROL TECHNOLOGY, COMPONENTS &SYSTEMS [2] BALDOR MOTORS AND DRIVES[SERVO CONTROL FACTS] [3] WWW.WIKIPEDIA.ORG [4] WWW.FREEPATENTSONLINE.COM 43 [Appendix C] Appendix C /***************************************************** This program was produced by the CodeWizardAVR V1.25.7a Standard Automatic Program Generator © Copyright 1998-2007 Pavel Haiduc, HP InfoTech s.r.l.