Speed Control Of Stepper Motor 5j5k64

Declaration This is to certify that this project and thesis is our original work. No part of this work has been submitted elsewhere partially or fully for the award of any other degree or diploma. Any material reproduced in this thesis has been properly acknowledged.

Students’ names & Signatures

1. RAHMAN MD. ASHIQUR ID: 06-06485-1

2. HOSSAIN MOHAMMAD ISMIAL ID: 06-06693-2

3. AHMED ISTIAQ ID: 06-06481-1

4. AHMED SAKIB ID: 06-06852-2

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Approval The thesis titled “Speed Control And Performance Evaluation Of a Stepper Motor” has been submitted to the following respected of the board of examiners of the faculty of Engineering in partial fulfillment of the requirements of the degree of Bachelor of Science in Electrical & Electronic Engineering on August ,2009 by the following students and has been accepted as satisfactory.

1. RAHMAN MD. ASHIQUR (06-06485-1) 2. HOSSAIN MOHAMMAD ISMAIL (06-06693-2) 3. AHMED ISTIAQ (06-06481-1) 4. AHMED SAKIB (06-06852-2)

_____________________________ Mr. Rinku Basak ( Supervisor ) Assistant Professor & Coordinator Dept. of Electrical And Electronic Engineering. American International University- Bangladesh

Mahmoodul Islam(External) Lecturer Dept. of Electrical And Electronic Engineering. American International University -Bangladesh.

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Prof. Dr. Tofazzal Hossain Dean –in- charge Department of Engineering American International University - Bangladesh

Dr. Carmen Z. Lamanga Vice chancellor American International University - Bangladesh

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ACKNOWLEDGEMENT

We would like to express our special thanks to our thesis advisor Mr. Rinku Basak, Assistant Professor & Coordinator, Faculty of Engineering, American International University- Bangladesh, for the ingenious commitment, encouragement and highly valuable advice he provided us over the entire course of this thesis. His rigorous attitudes to do the research and inspire thinking to solve problems are invaluable for our study career. We would like to appreciate Dr. Carmen Z. Lamanga , honorable Vice Chancellor , American International University- Bangladesh for her encouragements. We would like to appreciate Prof. Dr. Tofazzal Hossain , Dean-in-charge, Department of Engineering, American International University- Bangladesh for his encouragements. We would also like to thanks Mr. Masud , Lab supervisor for faculty of Engineering , of American International University- Bangladesh whose in valuable and irreplaceable experience help us get through lots of hardware related uncertainties . Next we would like to thanks our parents for their continues prayer and unbreakable belief in us through out our lives and also during the times of this project. Finally, we would like to express our hearties gratefulness to almighty Allah for his heavenly blessings without which it would not possible to complete this project successfully.

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CONTENTS

Declaration Approval Sheet Acknowledgement Abstract

(i) (ii) (iii) (vi)

Chapter 1: Introduction 1.1 1.2 1.3 1.4

Introduction Historical Background Objectives of this work Introduction to this thesis

Chapter 2: Theory and Operation of Stepper Motors 2.1 Introduction 2.2 Theory of operation of Stepper motors 2.3 Advantages of stepper motors 2.4 Disadvantages of stepper motors 2.5 Types of Stepper motors 2.6 Comparison between VR and PM stepper motor 2.7 Stepper motor switching sequences and step angle 2.8 Modeling of permanent magnet stepper motor 2.9 Stepper motor applications 2 10 Summary

Chapter 3: Circuit Description 3.1 Introduction 3.2 Hardware Overview 3.3 Summary Chapter 4: Circuit Implementation and Operation 4.1 Introduction 4.2 Implementation 4.3 Summary

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Chapter 5: speed control of a stepper motor 5.1 5.2 5.3: 5.4:

Introduction Rotating left turn and right turn Experimental Results Summary

Chapter 6: Discussions and Conclusions 6.1 6.2 6.3 6.4

Discussions Suggestions for future work Limitations of this circuit Conclusions

References:

Appendix:

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ABSTRACT

Despite model improvements and different control algorithms, much work remains to be done to attain maximum motor performance. This work attempts to achieve control and velocity tracking for a step motor using optimization techniques. The resulting system displays practical stabilization for velocity tracking of a voltage-fed permanent-magnet stepper motor. The control design is an output- design that utilizes stator current and rotor position measurements. The goal of this work is to design a controller that is rotted in anti clock or clock wise using controller , Xillinx software and PWM ( Pulse Width Modulation ).

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Chapter 1

Introduction 1.1 Introduction Stepper motors are used in a variety of applications, including high and low propulsion technology, computer peripherals, machine tools, robotics, etc. The interest in this system has been steadily increasing requirements for accuracy and repeatability while at the same time placing ever tighter demands on the maximum and constancy of speed as well as position resolution. However it has a non-linear and coupled dynamic structure so we could use different control schemes to make the stepper more competitive to use in different levels of application. Open loop control will provide a satisfactory solution under limited conditions. But for high performance dynamic operation this will not give satisfactory results. So we need to find more sophisticated control methods to make the performance of stepper motors much more competitive. We can do this by using newer techniques for drive control using fast semiconductor power switches and powerful microcontrollers made for motor application.

A stepper motor is a marvel in simplicity. It has no brushes or s and it is a synchronous motor with the magnetic field electronically switched to rotate the armature magnet. The essential function of a stepper motor is to translate switching excitation changes into precisely defined increments of rotor position. A stepper motor can be viewed as an electric motor without commentators .Typically, all the windings in the motor are part of the stator, and the rotor is either a permanent magnet, or in the case of variable reluctance motors, a toothed block of some magnetically soft material. A stepping motor system consists of three basic elements, often combined with some type of interface as shown in Fig 1.1. The first element, the indexer, is a microprocessor capable of generating pulses and direction signals to the driver . The second element is the driver and converts the indexer command signal into the power necessary to energize the motor winding.

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interface

Controller

High level command

Driver

Step pulses

Motor Motor current

Fig 1.1 Driving system of a Stepper Motor

The last element is the step motor which is an electromagnetic device that converts the digital pulses into mechanical shaft rotation. Advantages of step motors (compared to other types of motors) are low cost, high reliability, high torque at low speeds and a simple rugged construction that operates in almost any environment. The disadvantages of step motors are resonance effects at low speeds and decreasing torque with increasing speed.

1.2 Historical Background Stepper motors were developed in the early 1960's as a low cost alternative to position servo systems in the emerging computer peripheral industry. The main advantage of stepper motors is that they can achieve accurate position control without the requirement for position . In other words, they can run "open-loop", which significantly reduces the cost of a position control system. Stepper motors utilize a doubly-salient topology, which means they have "teeth" on both the rotor and stator. Torque is generated by alternately magnetizing the stator teeth electrically, and the permanent magnet rotor teeth try to line up with the stator teeth. There are many different configurations of stepper motors, and even more diverse ways to drive them. The most common stator configuration consists of two coils (A and B). These coils are arranged around the circumference of the stator in such a way that if they are driven with square waves which have a quadrature phase relationship between them, the motor will rotate. To make the motor rotate in the opposite direction, simply reverse

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the phase relationship between the A and B signals. A transition of either square wave causes the rotor to move by a small amount, or a "STEP". Thus, the name "stepper motor". The size of this step is dependent on the teeth arrangement of the motor, but a common value is 1.8 degrees, or 200 steps per revolution. Speed control is achieved by simply varying the frequency of the square waves. Because stepper motors can be driven with square waves, they are easily controlled by inexpensive digital circuitry and do not even require PWM. For this reason, stepper motors have often been inappropriately referred to as "digital motors". However, by utilizing power modulation techniques to change the quadrature square waves into sine and cosine waveforms, even MORE step resolution is possible. This is called "microstepping", where each discrete change in the sine and cosine levels constitutes one micro step . Theoretically, there is no limit to the position resolution achievable with microstepping, but in reality, it is limited by the motor mechanical and electrical tolerances. Some stepper motors are designed specifically for micro-stepping and consist of tightly matched impedances between the A and B coils, and tighter machining tolerances on the teeth at the expense of higher cost. Stepper motors are popular with digital control systems because they can be used in an open loop manner with predictable responses. Such applications include positioning heads in disk drives, adjusting fuel mixtures in automobiles, and controlling robot arms in robotics. Due to various disadvantages of DC motors in some applications they are increasingly begin replaced by servo motors or stepper motors Both types of motors offer similar opportunities for precise positioning but they differ in a number of ways. Servo motors require analog control systems of some type while stepper motors can run open loop. When making a choice between them, a number of issues that are application specific must be considered. From a control engineer’s perspective, the development of open loop or closed loop control involves modeling, and simulation of any system requires a thorough understanding of the system dynamics.

1.3 Objectives of this work The stepper motor is an easy and reliable device to convert electrical energy into mechanical motion. It does not have the accuracy or the response speed of a dc motor. It is however utilized in many applications such as disk drives, printers, recorders, plotters, copiers, scanners, fax machines, robots, machine tools, automobiles, and medical equipment for its ease of use. Since each input change causes exactly one step rotation, a stepper motor may be operated in an open loop system. 9

The motor used in the lab is a 4-phase, unipolar stepper motor. It has a step angle, a phase resistance, a phase inductance and a holding torque. Although there are discrete components controllers, stepper motor ICs will be used here. The motor phase connections and a typical control circuit are shown in the circuit diagram. The stepper motor will work with a 5V supply and should not be operated at higher than 200 steps per second. The easiest way to accomplish the task is to measure the input period of the pulse train using the IC function and store this value in a memory location. 1. To construct the stepper motor control circuit and test its operations without connecting it to the microcontroller. It can be done by using 0V and 5V signals to simulate the microcontroller outputs. 2. To develop the software necessary to “capture” the period of the input wave form .It must be done when any change is needed in the timer frequency will change the speed of the motor "immediately." 3. To write a data table to generate control signals to the stepper motor control circuit such that the motor functions consistently. It may be generated to control signals directly using the timer IC and use output port to send stepper control signals. 4. To test and demonstrate the operations of the bidirectional rotation system. 5. To show various calculations regarding stepper motor control.

1.4 Introduction to this thesis In chapter 2, the operation of various kinds of stepper motor have been described briefly and their switching sequence as well as their speed control have been explained. In chapter 3, all necessary devices that are used to control the speed of the stepper motor for example ( Motor Driver Chip (SN74194), the switching controller (SN7474), the pulse controller (LM555), fixed voltage controller (LM7805), N-MOSFET, Bipolar Junction Transistor (BJT), switch, potentiometer ) have been discussed.

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In chapter 4, the implementation of circuit that can be used for speed control of the stepper motor has been explained. In addition, synchronization of the PWM period is important for current sensing accuracy. We generate PWM signals to generate sine and cosine wave. By changing frequency we can change the control input which governs the current of the motor and we can change or control the speed of the motor. In chapter 5, the software overview where the PWM period has been described. In chapter 6, the experimental data and how to rotate clockwise or anticlockwise and control of step angles all have been described .

In chapter 7, problems occurred while deg this project and their probable solution were mentioned. Suggestion for future work will make in various aspects for deg of such circuits. Finally conclusions were made to this circuit. In references various books are websites which were helpful for this thesis, the name of the authors, publisher and edition number were provided. Finally appendix on this work with Xillinx software have discussed.

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Chapter 2

Stepper Motors

2.1 Introduction A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied to it in the proper sequence. The motors rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of motor shafts rotation. The speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied. A stepper motor (or step motor) is a brussless, synchronous electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely, without any mechanism (see open loop control). Stepper motors are similar to switched control motor (which are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.

Figure 2.1 : Stepper Motors

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A stepper motor has simplicity. It has no s and it is a synchronous motor with the magnetic field electronically switched to rotate the armature magnet. The essential function of a stepper motor is to translate switching excitation changes into precisely defined increments of rotor position .A stepper motor can be viewed as an electric motor without commutators .Typically, all the windings in the motor are part of the stator, and the rotor is either a permanent magnet, or in the case of variable reluctance motors, a toothed block of some magnetically soft material.

2.2 Theory of Operation of Stepper Motors Stepper motors provide means for precise positioning and speed control without the use of sensors. The basic operation of the stepper motor allows the shaft to move a precise number of degrees each time a pulse of electricity is sent to the motor. The shaft of the motor moves only the number of degrees that it was designed for when each pulse is delivered. We can control these pulses that are sent and control the positioning and speed. The rotor of the motor produces torque from the interaction between the magnetic field in the stator and rotor. The strength of the magnetic field is proportional to the amount of the current sent to the stator and number of turns in the windings .The stepper motor uses electromagnetic theory to make the motor shaft turn a precise distance when a pulse of electricity is provided. Like poles of a magnet repel and unlike poles attract. Figure 2.2 shows a typical cross-sectional view of the rotor and stator of a stepper motor. From this diagram we can see that stator has four poles, and the rotor has six poles. So the rotor will require 12 pulses of electricity to move the 12 steps to make one complete revolution. Another way to say this is that the rotor will move precisely 30 degrees for each pulse of electricity the motor receives. When no power is applied to the motor, the residual magnetism in the rotor magnets will cause the rotor to detent or align one set of its magnetic pole with the magnetic poles of one of the stator magnets. This means that the rotor will have 12 possible detent positions. When the rotor is in a detent position, it will have enough magnetic force to keep the shaft from moving to the next position. This is what makes the rotor feel like it is clicking from one position to the next as you rotate the rotor by hand with no power applied.

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Figure 2.2 : Six Pole Rotor and Four Pole Stator in a Stepper Motor

When power is applied, it is directed to only one of the stator pairs of windings, which will cause that winding pair to become a magnet. One of the coils for the pair will become the north pole, and the other will become the south pole. When this occurs, the stator coil that is the north pole will attract the closest rotor tooth that has the opposite polarity, and the stator coil that is the south pole will attract the closest rotor tooth that has the opposite polarity. When current is flowing through these poles, the rotor will now have a much stronger attraction to the stator winding, and the increased torque is called the holding torque. By changing the current flow to the next stator winding, the magnetic field will be changed 90°. The rotor will only move 30° before its magnetic fields will again align with the change in the stator field. The magnetic field in the stator is continually changed as the rotor moves through the 12 steps to move a total of 360°. Figure 2.2 shows the position of the rotor changing as the current supplied to the stator changes .In Fig. 2.2 we can see that when current is applied to the top and bottom stator windings, they will become a magnet with the top part of the winding being the north pole, and the bottom part of the winding is the south pole. We should notice that this will cause the rotor to move a small amount so that one of its south poles is aligned with the north stator pole (at the top). The opposite end of the rotor pole, which is the north pole, will align with the south pole of the stator (at the bottom). A line is placed on the south pole piece that is

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located at the 12 o'clock position in Fig. 2.3a so that we can follow its movement as current is moved from one stator winding to the next. In Figure 2.3b current has been turned off the top and bottom windings, and current is now applied to the stator windings shown at the right and left sides of the motor. When this occurs, the stator winding at the 3 o'clock position will have the polarity for the south pole of the stator magnet, and the winding at the 9 o'clock position will have the north-pole polarity. In this condition, the next rotor pole that will be able to align with the stator magnets is the next pole in the clockwise position to the previous pole. This means that the rotor will only need to rotate 30° in the clockwise position for this set of poles to align with the stator poles.

Figure 2.3: One Quarter Revolution of a Two-Phase Six-Pole Stepper Motor

In Fig. 2.3c we can see that the top and bottom stator windings are again energized, but this time the top winding is the south pole of the magnetic field and the bottom winding is the north pole. This change in magnetic field will cause the rotor to again move 30° in the clockwise position until its poles will align with the top and bottom stator poles. We

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should notice that the original rotor pole that was at the 12 o'clock position when the motor first started has now moved three steps in the clockwise position . In Figwe can see that the two side stator windings are again energized, but this time the winding at the 3 o'clock position is the north pole. This change in polarity will cause the rotor to move another 30° in the clockwise direction. We should notice that the rotor has moved four steps of 30° each, which means the rotor has moved a total of 120° from its original position. This can be verified by the position of the rotor pole that has the line on it, which is now pointing at the stator winding that is located in the 3 o'clock position.

2.3 Advantages of stepper motors (a) Position error is non cumulative. A high accuracy of motion is possible, even under open-loop control. (b) Large savings in sensor (measurement system) and controller costs are possible when the open-loop mode is used. (c) Because of the incremental nature of command and motion, stepper motors are easily adaptable to digital control applications. (d) No serious stability problems exist, even under open-loop control. (e) Torque capacity and power requirements can be optimized and the response can be controlled by electronic switching. (g) Brushless construction has obvious advantages.

Open Loop Operation One of the most significant advantages of a stepper motor is its ability to be accurately controlled in an open loop system. Open loop control means no information about position is needed. This type of control eliminates the need for expensive sensing and devices such as optical encoders. .

2.4 Disadvantages of stepper motors (a) They have low torque capacity (typically less than 2,000 oz-in) compared to DC motors. (b) They have limited speed (limited by torque capacity and by pulse-missing problems due to faulty switching systems and drive circuits).

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(c) They have high vibration levels due to stepwise motion. (d) Large errors and oscillations can result when a pulse is missed under open-loop control. (e) Low output power for size and weight. (f) Low efficiency ,Motor draws substantial power regardless of load. (g) Motor gets high performance configurations. (h) Motor is audibly very noisy at moderate to high speeds.

2.5 Types of Stepper Motors Three basic types of stepper motors include the permanent magnet motor, the variable reluctance motor, and the hybrid motor, which is combination of previous two.

Permanent Magnet (PM) Stepper Motor A PM stepper motor operates on the reaction between a permanent-magnet rotor and an electromagnetic field. Figure 2.5.1 shows a cutaway diagram of a typical permanent magnet stepper motor. The rotor shows that the permanent magnet motor can have multiple rotor windings, which means that the shaft for this type of stepper motor will turn fewer degrees as each pulse of current is received at the stator .

Figure 2.4: Diagram of a Permanent Magnet Stepper Motor 17

For example, if the rotor has 50 teeth and the stator has 8 poles with 5 teeth each (a total of 40 teeth), the stepper motor is able to move 200 distinct steps to make one complete revolution. This means that shaft of the motor will turn 1.8° per step. The main feature of the permanent magnet motor is that a permanent magnet is used for the rotor, which means that no brushes are required. The drawback of this type of motor is that it has relatively low torque and must be used for low-speed applications. If no power is applied to the windings a small amount of magnetic force is developed between the permanent magnet and the stator. This magnetic force is called a residual or detent torque. The detent torque can be noticed by turning a stepper motor by hand and is generally about one-tenth of the holding torque . The PM stepper motor has to overcome the detent torque to line up with the stator field when a steady DC signal is applied to the stator winding.

Variable Reluctance Stepper Motor The variable-reluctance (VR) stepper motor at its core basically differs from the PM stepper in that it has no permanent-magnet rotor and thus no residual torque to hold the rotor at one position when turned off. This means the field strength can be varied. The stator of a variable-reluctance stepper motor has a magnetic core constructed with a stack of steel laminations. The rotor is made of demagnetized soft steel with teeth and slots, or any other such magnetically permeable substance, unlike PM stepper motors.. When the stator coils are energized, the rotor teeth will align with the energized stator poles. In the non-energized condition there is no magnetic flux in the air gap so there is no detent torque. This type of motor operates on the principle of minimizing the reluctance along the path of the applied magnetic field. By alternating the windings that are energized in the stator, the stator field changes, and the rotor moves to a new position .

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Figure 2.4: Cross Section and side view of VR Stepper Motor . The motor shown in Fig 2.5.2 has four rotor teeth 90 degrees from each other and six poles 60 degrees apart from each others. So when the winding are energized in the recurring sequence of 2, 3, 1, and then the motor will rotate 30 degrees per step. This motor will provide less torque at standstill than PM motor but dynamic torque characteristics are better. The VR stepper motors mentioned up to this point are all single-stack motors. That is, all the phases are arranged in a single stack, or plane. The disadvantage of this design for a stepper motor is that the steps are generally quite large (above 15°). A variation to this scheme is the multitask stepper motor that can produce smaller step sizes because the motor is divided along its axial length into magnetically isolated sections, or stacks .

Hybrid Stepper Motor Construction of PM stepper motor becomes very complex below 7.5 deg step angles. Smaller step angles can be realized by combining permanent magnet stepper motor and variable reluctance stepper motor. Torque is created in the hybrid motor by the interaction of the magnetic field of the permanent magnet and the magnetic field produced by stator windings

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. Fig 2.5:Cross Section of a Hybrid Stepper Motor A typical hybrid motor is shown in Fig. 2.5.3. The stator construction is similar to the permanent magnet motor, and the rotor is cylindrical and magnetized like the PM motor with multiple teeth like a VR motor. The teeth on the rotor provide a better path for the flux to flow through the preferred locations in the air gap. This increases the detent, holding, and dynamic torque characteristics of the motor compared to the other two types of motors. Hybrid motors have a smaller step angle compared to the permanent magnet motor, but they are very expensive. In low cost applications, the step angle of a permanent magnet motor is divided into smaller angles using better control techniques. Permanent magnet motors and hybrid motors are more popular than the variable reluctance motor, and since the stator construction of these motors is very similar, a common control circuit can easily drive both types of motors.

2.6 Comparison between VR and PM Stepper Motors In general Hybrid/PM steppers have great step resolution which is advantageous when high angular position resolution is needed. On the other hand variable reluctance steppers are useful in applications where a load is to be moved a considerable distance, due to their large step size, with fewer number of excitations. PM motors produce a small amount of detent torque that helps in preserving the position even after current

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excitations in the windings are removed. This also proves to be a disadvantage as they have a large mechanical inertia compared to VR motors. With its wide range of applications and simple understandable physics PM stepper motors are of great interest to control engineers. In this work we focus on investigating a new control methodology for PM steppers . The speed of a stepper motor depends on the rate at which it can turn on and off the coils, and is termed the step-rate. The maximum step-rate, and hence the maximum speed, depends upon the inductance of the stator coils. Figure 2.6 shows the relation between current rise and winding inductance. It takes a longer time to build the rated current in a winding with greater inductance compared to a winding with lesser inductance. So, when using a motor with higher winding inductance, sufficient time needs to be given for current to build up before the next step command is issued. If the time between two step commands is less than the current build-up time, it results in a slip, i.e., the motor misses a step. Unfortunately, the inductance of the winding is not well documented in most of the stepper motor data sheets. In general, for smaller motors, the inductance value of the coil (in henrys) is much less than its resistance value (in ohms) so the time constant is small. With a lower time constant, current rise in the coil will be faster, which enables a higher step-rate.

Fig 2.6: Current Rise Rate and Torque vs. Speed Relationship in Stator winding .

2.7 Stepper Motor Switching Sequence and step angle Stepper Motor Switching Sequence

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To enable rotation of the rotor the magnetic field generated by the stator windings has to interact and drive the rotor flux, which is achieved by switching the direction of current flow through each winding. The switching sequences for the stepper motor are as described below. Full step : The stepper motor uses a four-step switching sequence, which is called a fullstep switching sequence. Each of the windings is tapped at one end and they are connected through a resistor to the negative terminal of the power supply . F

Figure 2.7: Switching Circuit and Sequence Table for Full Step Mode. The table in Figure shows the sequence for energizing the coils. During the first step of the sequence, switches SW1 and SW3 are on and the other two are off. During the second step of the sequence, switches SW1 and SW4 are on and the other two are off. During the third step of the sequence, SW2 and SW4 are on and the other two are off. During the fourth step of the sequence, SW2 and SW3 are on and the other two are off. This sequence continues through four steps, and then the same four steps are repeated again. These steps cause the motor to rotate one step or tooth on the rotor when a pulse is applied by closing two of the switches. This “Two Phase On” method gives 41.4 % more torque compared to “One Phase On” method.

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Half-step: A nother switching sequence for the stepper motor is called an eight-step or half-step sequence. The switching diagram for the half-step sequence is shown in Fig. 2.8 . The main feature of this switching sequence is that you can double the resolution of the stepper motor by causing the rotor to move half the distance it does when the full-step switching sequence is used. This means that a 200-step motor, which has a resolution of 1.8°, will have a resolution of 400 steps and 0.9°. The way the controller gets the motor to reach the half-step is to energize both phases at the same time with equal current U

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Figure 2.8: Switching Circuit and Sequence Table for Half Step Mode. In this sequence the first step has SW1 and SW3 on, and SW2 and SW4 are off. The sequence for the first step is the same as the full-step sequence. The second step has SW1 on and all of the remaining switches are off. This configuration of switches causes the rotor to move an additional half-step. The third step has SW1 and SW4 on, and SW2 and SW3 are off, which is the same as step 2 of the full-step sequence. The sequence continues for eight steps and then repeats. The main difference between this sequence and the full-step sequence is that steps 2, 4, 6, and 8 are added to the full-step sequence to create the half-step moves

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Micro-step: The full-step and half-step motors tend to be slightly jerky in their operation as the motor moves from step to step. The amount of resolution is also limited by the number of physical poles that the rotor can have. The amount of resolution (number of steps) can be increased by manipulating the current that the controller sends to the motor during each step. Also we can reduce the resonance problem using micro-stepping at a low step rate. For that the current can be adjusted so that it looks similar to a sine wave. U

U

Figure 2.9: Phase current diagram in micro-step mode. Figure 2.9 shows the waveform for the current to each phase. From this diagram we can see that the current sent to each of the two sets of windings is timed so that it is always out of phase with each other. The fact that the current to each individual phase increases and decreases like a sine wave and cosine wave that is always out of time with the other phase will allow the rotor to reach hundreds of intermediate steps. The voltage sent to the motor is now an approximate sine wave. The motor for this type of application is generally a permanent magnet brushless DC motor. The motor windings will require a capacitor to be wired in series for this type of application. Micro-stepping is a relatively new stepper motor technology that controls the current in the motor winding. Advantages and disadvantages of micro winding : The major advantage using micro-stepping technique is as below: 1. Smooth movement at low speeds. 2. Increased step positioning resolution as a result of smaller step angle. 3. Maximum torque at both low and high step rates. The major disadvantage of the micro-stepping technique is as below: 24

1. If static friction is in the system, the angular precision is limited. 2. Detent torque needs to be overcome because of the non-sinusoidal characteristic of PM stepper motor. 3. Cost of implementation. We will discuss this technique more in the next chapter, as this technique was used in this thesis to drive the stepper motor.

Step angle The step angle, the number of degrees a rotor will turn per step, is calculated as follows: Step Angle (B) = 360 degrees/ S S = mNr where m = Number of phases. Nr = Number of rotor teeths. For this motor m=3 Nr = 4 S = mNr = 3*4 = 12 Step Angle ,B = 360/12 = 30 degrees per step

2.8 Modeling of permanent magnet stepper motor In order to investigate the dynamics of mechanisms driven by stepper motors a model had to be created. With a minimum background of basic laws of electromagnetism and motor physics, this section provides a brief derivation of a nonlinear model of the 2-phase PM stepper motor shown in Figure 2.8.

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Figure 2.10: Four Pole PM stepper Motor. As explained earlier, when the windings of a phase are energized, a magnetic dipole is generated on the stator side. If for example phase 2 is active (phase 1 is switched off), winding 3 produces an electrical north pole and winding 4 a South Pole.

2.9 Applications of Stepper motors Stepper motors are used in a wide variety of applications in industry, including computer peripherals, business machines, motion control, and robotics, which are included in process control and machine tool applications. A partial list of applications is shown below . 1. Computer Peripherals: Floppy disk Printer Tape Reader Plotter 2. Business Machines: Card Reader Copy Machine Banking system Type Writer Card sorter

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3. Process Control: Valve control Conveyor Assembly lines Laser trimming Mail handling system 4. Machine Tools: Milling Machine Drilling Machine Grinding Machine Laser Cutting Sewing

2 10 Summary In this chapter different types of stepper motors, their applications and the advantages and disadvantages of stepper motors have been described. Also the switching sequence and step angle have been discussed in this chapter. Moreover the application of the stepper motors has been discussed .

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Chapter 3

Circuit Description and Hardware Implementation

3.1 Introduction Stepper motors are used in a variety of applications, including high and low propulsion technology, computer peripherals, machine tools, robotics, etc. The interest in this system has been steadily increasing requirements for accuracy and repeatability while at the same time placing ever tighter demands on the maximum and constancy of speed as well as position resolution. However it has a non-linear and coupled dynamic structure so we could use different control schemes to make the stepper more competitive to use in different levels of application. Open loop control will provide a satisfactory solution under limited conditions. But for high performance dynamic operation this will not give satisfactory results. So we need to find more sophisticated control methods to make the performance of stepper motors much more competitive. We can do this by using newer techniques for drive control using fast semiconductor power switches and powerful microcontrollers made for motor application. Stepper motors operate differently from normal DC motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, such as a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one, and from there the process is repeated. Each of those slight rotations is called a "step," with an integral number of steps making a full rotation. In that way, the motor can be turned by a precise angle.

Circuit Diagram of this work Circuit Diagram of this work below:

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Figure 3.1: Circuit Diagram of this work.

3.2 Hardware Overview In this thesis some kinds of hardwares are used to control the speed of a stepper motor . Those hardwares have been described below:-

The Stepper Motor The operation of a stepper motor requires the presence of the following elements : (a) A control unit ( a micro-processor for example) which supplies impulses the frequency of which is proportional to the speed of the motor. This applies equally to both directions of rotation; (b) A sequencer which will direct the impulses to the various motor coils (c) A power supply.

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Motor Driver Chip (SN74194)

Introduction A 74194 - Bidirectional Universal Shift from the 74LS or 74HC - TTL families of logic devices to produce the stepping pattern. If the motor is some distance from the circuit board or power supply, it might be best to separate the motor's power supply lead from the circuit board's supply as illustrated in the next diagram. The motor could be connected using larger gauge wire. This will keep most effects of the motors current pulses away from the supply to the circuit board. A filter capacitor could be placed in the motor's supply circuit as well

Features The Step rate adjustment range of the drivers is 0.(1.39 sec) to 145 steps per second. (Lower and higher step rates are also possible.). The only step angle for these drivers is the design step angle of the motor itself. 'Halfstepping' is not possible with either of the driver circuits. A 74194 - Bidirectional Universal Shift from the 74LS or 74HC - TTL families of logic devices to produce the stepping pattern. For a 12 volt supply, external circuits can draw up to 100 milliamps. For a 24 volt supply, external circuits can draw up to 25 milliamps.

Pin Configuration(SN74194) IC SN74194 is a IC of 16 pins. The function of these pins are : (a) (b) (c) (d)

Pins (1, 3, 16) are used for biasing. Pins (4, 5, 6, 8) are used for ground. Pin 11 is used for taking input pulses Pins (12, 13, 14, 15 ) are used for output ports.

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GRD

Figure 3.2: Pin configuration of IC SN74194. (e) Pins (9, 10 ) are driver pins used to toggle the rotation of the stepper motor .

SN74194 driver initialization When power is applied to the 74194 Stepper Driver circuit there is a very short delay before stepping of the outputs can begin. The delay is controlled by a capacitor, resistor and transistor . The function of the delay is to allow the outputs of IC74194 to be set with pin 12 in a HIGH state and pins 13, 14 and 15 in a LOW state before direction control becomes active. The delay also prevents IC555 from oscillating until IC74194 has been set. If the power to the circuit is turned off, there should be a pause of at least 10 seconds before it is reapplied. The pause is to allow a capacitor to discharge through a resistor and a diode.. .

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The switching controller (SN7474) Introduction These devices contain two independent D-type positive edge triggered flip-flops. A low level at the preset or clear inputs sets or resets the outputs regardless of the levels of the inputs. When preset and clear are inactive , data at the D input meeting the setup time requirements are transferred to the outputs on the positive going edge of the clock pulse Clock triggering occurs at a voltage level and is not directly related to the rise time of the clock pulse. Following the hold time interval , data at the input may be changed without affecting the levels at the outputs.

Features (a) (b) (c) (d) (e) (f) (g)

Supply voltage range ( Minimum 4.25v, Normal 5.00v, Maximum 5.25v ) High level input voltage ( Minimum 2.00v ). Low level input voltage ( Maximum 0.80v ). High level output voltage ( Minimum -0.40v ). Low level output voltage ( Maximum 16.00v ). Pulse duration ( CLK high, Minimum 30ms, CLK low, Minimum 37ms ). Operating free air temperature ( Minimum 00 C, Maximum 700 C) .

Pin Configuration(SN7474) The switching controller IC (SN7474) consists of 14 pins. The function of the pins have defined in below: (a) Biasing pins : 1, 13, 14 pins are used for biasing. (b) Ground pins : 7. 12 are connected with ground. (c) Output pins : 3, 8 pins are used for the output.

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Figure 3.3: Pin configuration of IC SN7474. For this thesis , pins ( 1,13,14,10,4 ) are shorted for biasing voltage 5v. Pins ( 2,6,11 ) are shorted for toggle. Pins (3, 8 ) are used for output, pin no 3 is used for giving pulse to the IC SN 74194 and the output from pin 8 is used to control the pin of 10 and 9 of the IC 74194.

Description Generally IC SN7474 is called the switching controller IC. There some limitation in supply voltage , high level input voltage , low level input voltage as well as high level output voltage and low level output voltage It is operated in Minimum 00 C to maximum 700 C.

The pulse controller (LM555)

Introduction Applications such as oscillators, pulse generator, ramp or square-wave generator, one shot multivibrators and voltage monitors all require a circuit capable of producing timing intervals. The most popular integrated circuit timer is the 555 , first introduced by Signatics Corporation. Like general purpose op-amps, the 555 is reliable, easy to use in a variety of applications, and low in cost. The 555 can also operate from supply voltage of

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+5v to +18v, making it compatible with both TTL( transistor-transistor logic) circuits and op amp circuits.

Features (a) (b) (c) (d) (e) (f) (g) (h) (i)

Two operation modes ( astable and monostable). For astable don’t need any input. For monostable input is needed. Maximum voltage is not equal to the Vcc. The output voltage will may be 2/3Vcc or less than 2/3Vcc. The minimum value of output voltage is 0.1v but does not 0. Reset will always high otherwise output will be 0. There is a charging path and discharging path. Biasing voltage is generally 5v.

Pin Configuration (a) Pin 1 is used for ground pin. (b) Pin 2 is used for trigger. (c) Pin 3 is used for out port port. (d) Pin 4 is used for reset. (e) Pin 5 is controlled the Vcc voltage. (f) Pin 6 is used for comparing threshold voltage (g) Pin 7 is called is discharging pin, where the current is discharged. (h) Pin 8 is used for applying Vcc or biasing voltage. .

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Figure 3.4: Internal Circuit diagram of 555 timer.

Description The 555 IC timer has two modes of operation, either as an astable mutivibrator or as a monosthable multivibrator. Free running operation of the 555 in figure. The output voltage switches from a high to low state and back again. The time the output is either high or low is determined by a resistor – capacitor network connected externally to the 555 timer. The value of the output voltage is less than Vcc. When the timer is operated as a one-shot multivibrator , the output voltage is low until a negative going trigger pulse is applied to the timer, then the output switches is high. The time the output is high determined by a resistor and capacitor connected to the IC timer. IC555 timer can be used in Programmable timer counter (XR-2240) as well as in speed control of the stepper motor circuit.

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Figure 3.5: Free – running operation

Fixed voltage controller (LM7805)

Introduction

Voltage regulators produce fixed DC output voltage from variable DC (a small amount of AC on it). Normally we get fixed output by connecting the voltage regulator at the output of the filtered DC(see in above diagram). It can also used in circuits to get a low DC voltage from a high DC voltage (for example we use 7805 to get 5V from 12V). There are two types of voltage regulators 1. fixed voltage regulators(78xx,79xx) 2. variable voltage regulators(LM317) In fixed voltage regulators there is another classification 1. +ve voltage regulators 2. -ve voltage regulators

Features (a) (b) (c) (d) (e) (f)

Output current up to 1A Thermal overload protection Thermal overload protection Output voltage of 5, 6, 8, 9, 10, 12, 18, 24v Short circuit protection Output transistor safe operating area protection.

Pin Configuration

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To identify the leads of the 7805, first have to keep the lead downward and the writing to in front of the side, the figure below. The heat sink above the voltage regulator.(1 input,2-gnd,3-output) .

Figure 3.6: Regulator IC7805

This is the same way of lead identification for all 3 terminal IC's (for . Power transistor).

Figure 3.7: Construction of Regulator IC7805

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The above diagram show how to use 7805 voltage regulator. Here the coupling capacitors are used for good regulation. But there is no need for it in normal case..But using 7805 in analog circuit using capacitor is badly needed, otherwise the noise in the output voltage will be high. The mainly available 78xx IC's are 7805,7809,7812,7815,7824.

Description

Positive voltage regulator: This include 78xx voltage regulators. The most commonly used ones are 7805 and 7812 gives fixed 5V DC voltage if input voltage is in (7.5V,20V).Regulation won't be proper if input voltage is <7.5 V or some 3V. If input is 6V then output may be 5V or 4.8V, but there are some parameters for the voltage regulators like maximum output current capability, line regulation etc.. , that parameters won't be proper. For applying 3.55V , can be got around 3.5V. that electronics components should be used in the proper voltage and current ratings In this project, a commercially produced circuit board with an on-board 7805 regulator. It was designed to be powered from 9-12 volts input to the regulator.

Negative voltage regulator Mostly available -ve voltage regulators are of 79xx family. For IC741 +12v and -12v will be enough, even though in most circuits can be used +15v and -15v.

N-MOSFET Introduction MOSFET s are further broken down into depilation type and enhancement define their basis mode of operation. The name of the MOSFET is metal oxide semiconductor field effect transistor. Features

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(a) To prevent the gate leakage current NMOSFET is used . (b) For JFET, an appreciable amount of gate current will flow which will reduce the amplitude of the input signal NMOS is free from this disadvantage. To overcome this disadvantage the gate terminal is insulated from the channel with a thin layer of silicon dioxide. (c) An negative voltage is applied to the gate terminal which will repel electrons from the n channel and reduce drain current.

Pin Configuration Normally NMOSFET has three pins ( Gate , Drain and Source ). For the following figure ( 1pin – gate, 2pin – drain and 3 pin- source ) Gate is used for input , drain is used for output and source is used for ground.

Figure 3.8 : Pin configuration of NMOSFET Description The basic construction of the NMOS is provided on the figure , a slap of p-type material is form a silicon base and is referred to as a substrate. It is the foundation on which the

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device is constructed. In some cases the substrate is internally connected to the source terminal. The source and drain terminals are connected throw metallic to n dope region linked by an n – channel as shown in the figure. The gate is also connected to a metal surface but remains insulated from the n channel by a very thin SiO2 layer. Sio2 is a type of insulator refer to as a dielectric. Operating modes (a) Accumulation (b) Depletion (c) Inversion

Figure 3.9 : Construction diagram of NMOSFET

Bipolar Junction Transistor (BJT) Introduction The transistor is a three – layer semiconductor device consisting of either two n and one p type layers of material or two p- and one n-type layers of material. The former is called and npn transistor, and the latter is called a pnp transistor . At lower end of the active 40

region the emitter current is zero, and the collector current is simply that due to the reverse saturation current. As in figure . Base current which is insert to the base terminal.

Figure 3.10: Construction of Bipolar Junction Transistor ( BJT )

Features (a) Base to emitter voltage may be 0.7 v. (b) When base current will less than or equal to 0 μA it will be called cutoff region. (c) The BJT device could be biased to operate outside of the maximum limits.

Pin Configuration

Figure 3.11 : Pin configuration of NPN BJT

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(a) Pin 1 indicates the emitter. (b) Pin 2 indicates the base. (c) Pin 3 indicates the collector.

Description A transistor is a three layer semiconductor device consisting of either two n-type and ptype layers pf materials or two p and one n-type layer of material. The former is called an npn transistor, and the latter is called a pnp transistor. The operation of npn transistor is exactly the same if the roles played by the electron and hole are interchanged. The depletion region has been reduced in width due to the apply bias , resulting in a heavy flow of majority carriers from the p-type to n type material For starting BJT at first it should be biased. The biasing voltage of BJT is more than 5 volt. There are three terminals in BJT : (a)

Gate – this terminal is connected to the input device

(b)

Drain – this terminal is connected to the positive node of the power source

(c)

Source – this is the source of electrons required for conductivity

Basic Circuit Components The basic componenets are : (a) Resistors (b) Capacitors (c) Potentiometer (d) Diodes (e) Switches

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Summary In this chapter the components of this thesis has been described. The most common device is IC SN74194 which is called as a driving device. Some other devices which are essential such as pulse controller, voltage controller device. Voltage controller device is used to save the circuit components. The pulse controller is controlled to give the pulse for controlling the driver IC. Some basic components ( resistors, capacitors, diodes ) are used for help of the circuit implementation.

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Chapter 4

Circuit Implementation and Observation 4.1 Introduction Speed control of a stepper motor is necessary for various applications. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied to it in the proper sequence. The motors rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of motor shafts rotation.

4.2 Implementation To control the stepper motor various kinds of components have been used. Some resistors, capacitors , some variable ICs ( for example driving IC, controller IC, regulated IC etc) , switches, LED s have been used. From Voltage controller IC 7805 gives constant 5 volt which is used for biasing IC SN74194, LM555, SN7474. LM555 give pulses for SN74194 in the pin of 11 of SN74194. Pin 7 and 15 , 2 and 12 are shorted of SN74194, and pin 12, 13, 14, 15 are used for output. 4, 5, 6, 8 are shorted and connected with ground. The pin 9 and 10 of SN74194 are connected with two LED s , it will indicate the circuit works. Controlling IC SN7474 control the pulse for SN74194. Four outputs are connected with four windings of the stepper motor that will be controlled with its speed. Some resistors are used to save the IC s. Generally two LED s are used ( in figure ) . For Q1 motor rotted clockwise and for Q2 rotted anticlockwise. Some diodes are used for indicating forward direction.

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Figure 4.1 : Implementation circuit to speed control of a stepper motor

From SN7474 get two outputs , one is connected with two LED s and another is connected with pin 11 of SN74194 for controlling the pulse. For biasing more than 5 volt can be used but for safety 5 volt is perfect for this circuit implementation. SN7805 control this voltage. We can also use Johnson counter and ring counter as a shift to implement this experiment.We can also use XR2240 IC as a timer for large time period. Description of this components have explained below:

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Shift Counters Two of the most common types of shift counters are introduced here: the Ring counter and the Johnson counter. They are basically shift s with the serial outputs connected back to the serial inputs in order to produce particular sequences. These s are classified as counters because they exhibit a specified sequence of states.

Ring Counters A ring counter is basically a circulating shift in which the output of the most significant stage is fed back to the input of the least significant stage. The following is a 4-bit ring counter constructed from D flip-flops. The output of each stage is shifted into the next stage on the positive edge of a clock pulse. If the CLEAR signal is high, all the flip-flops except the first one FF0 are reset to 0. FF0 is preset to 1 instead.

(a)

(b) Figure 4.2 : Ring Counter

Flip Flop outputs are FF0,FF1,FF2,FF3 are 1, 0, 0, 0.Since the count sequence has 4 distinct states, the counter can be considered as a mod-4 counter. Only 4 of the maximum 16 states are used, making ring counters very inefficient in of state 46

usage. But the major advantage of a ring counter over a binary counter is that it is selfdecoding. No extra decoding circuit is needed to determine what state the counter is in.

Johnson Counters A Johnson counter (or switchtail ring counter, twisted-ring counter, walking-ring counter, or Moebius counter) is a modified ring counter, where the output from the last stage is inverted and fed back as input to the first stage.[1][2][3] A pattern of bits equal in length to twice the length of the shift thus circulates indefinitely. These counters find specialist applications, including those similar to the decade counter, digital to analogue conversion, etc.

(a)

(b) Figure 4.3 : Johnson Counter Flip Flop outputs are FF0,FF1,FF2,FF3 are 0, 0, 0, 0. Johnson counters are a variation of standard ring counters, with the inverted output of the last stage fed back to the input of the first stage. They are also known as twisted ring counters. An n-stage Johnson

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counter yields a count sequence of length 2n, so it may be considered to be a mod-2n counter. The circuit above shows a 4-bit Johnson counter. The state sequence for the counter is given in the table as well as the animation on the left. Again, the apparent disadvantage of this counter is that the maximum available states are not fully utilized. Only eight of the sixteen states are being used. Beware that for both the Ring and the Johnson counter must initially be forced into a valid state in the count sequence because they operate on a subset of the available number of states. Otherwise, the ideal sequence will not be followed. We can also use this IC 4017 as a counter.

IC 4017

Figure 4.4 : IC 4017

Pin Configuration(IC 4017)

Figure 4.4 : IC 4017(pin diagram) 48

General Description of XR2240 The XR-2240 Programmable Timer is a monolithic controller capable of producing ultralong time delays with sacrificing accuracy. In most applications it provides a direct replacement for mechanical or electromechanical timing devices and generates programmable time delays from microseconds up to five days. Two timing circuits can be cascaded to generate time delays up to three years. As shown in figure 4.5 the circuit is comprised of an internal time base oscillator , a programmable 8 bit counter and a flip-flop .The time delay is set by an external R-C network and can be programmed to value from 1 RC to 255 RC. In astable operation , the circuit can generate 256 separate frequencies or pulse-patterns from a single RC setting and can be synchronized with external clock signal. Both the control inputs and outputs are compatible with TTL and DTL logic levels.

Figure 4.5 : IC XR2240 (pin diagram)

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Features Timing from micro-seconds to days Programmable delays : 1 RC to 255 RC. Wide supply range : 4V to 15V. TTL and DTL compatible output. High accuracy : 0.5% External Sync and Modulation capability. Excellent Supply Rejection : 0.2%N

4.3 summary

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Chapter 5

Speed control of a stepper motor

5.1 Introduction In this work a technique for controlling the stepper motor has been developed. The rotating properties and then implementation of the control algorithm in actual hardware to get experimental test results.

5.2 Stepper Motors and Driving Methods Often a mechanical operation or function is required in an application. This may in turn require a motor or other mechanical device to position a load or device .Examples are computer peripherals (scanners, disc drives, etc), camera, telescope and satellite dish positioning systems, robotic arms, and numerically controlled machine tools. While a conventional DC or AC motor can be used, it is difficult to accurately determine the exact position of the load, motor speed, or how much total motion has been produced, unless external positioning sensors, encoders, servo loops, and controlling devices (brakes, clutches, etc) are used. Many motors run at a speed in RPM that is too high, and this involves using a gear train to reduce the speed and increase the torque to useable levels. While this may not always be a problem, conventional motors can be difficult to use for certain applications. Where very high speed is not a factor and precise control is desired, a stepper motor may be advantageous. Many applications require lower speeds, below a few hundred revolutions per minute, and often conventional type motors include integral gear speed reduction systems. A stepper motor is a device that translates an electrical signal to a change in position of a shaft or other actuator. This is usually a linear translation or rotation. Unlike a conventional DC or AC motor, this is usually a discrete quantity, and occurs when a pulse or other signal is applied. While DC or AC motors are driven continuously, a stepper motor is driven generally by pulses. Stepper motors are somewhat similar to reluctance motors, i.e. they depend on attraction or repulsion of magnetic structures and derive their torque solely on the change of reluctance of a magnetic circuit, whereby a conventional motor derives its torque from the interaction of current carrying conductors with magnetic fields. A stepper motor cannot draw a higher current in a stalled rotor condition, to rapidly accelerate a load from rest to speed. This stalled rotor condition is momentarily encountered during startup of conventional motors due to mechanical inertia. It causes an initially high current to be drawn by the motor. DC 51

and AC motors can, within reason, draw the higher current they need to start up quickly. Stepper motors depend on reluctance torque only, so they can not start up as large a load as a comparable conventional motor. A stepper motor will move a load a certain discrete amount for each pulse applied, then stop and do nothing until another pulse is applied.

5.3 Rotating left turn and right turn When a phase winding of a stepper motor is energized with current, a magnetic flux is developed in the stator. The direction of this flux is determined by the “Right Hand Rule” which states: “If the coil is grasped in the right hand with the fingers pointing in the direction of the current in the winding (the thumb is extended at a 90angle to the fingers), then the thumb will point in the direction of the magnetic field.” The rotor then aligns itself so that the flux opposition is minimized. In this case the motor would rotate clockwise so that its south pole aligns with the north pole of the stator A and its north pole aligns with the south pole of stator B. To get the motor to rotate we can now see that we must provide a sequence of energizing the stator windings in such a fashion that provides a rotating magnetic flux field which the rotor follows due to magnetic attraction. The armature or moving part, is a magnetic structure that may be only soft iron, (reluctance type) or may be a permanent magnet itself (hybrid type). Several electromagnets (poles), called the stator, are arranged around the armature, or rotor. When the electromagnets are energized as shown, the rotor will turn until it lines up with the opposite poles. If two adjacent stator magnets are energized so that the polarity is the same, the rotor will tend to line up between these poles such that the magnetic circuit has minimum reluctance, which is the easiest path for the magnetic lines of force. After this occurs, nothing else will happen. The electromagnets have a steady state current now flowing in their windings. The current flow will hold the rotor in position and a certain externally applied torque will be needed to move the rotor out of this position. This current flow acts as a brake, and therefore no external brake mechanism is needed. This force will be from several inch-ounces to several hundred inch ounces, depending on the motor. Motors with a permanent magnet rotor have a residual magnetism present and therefore a braking effect still exists with no current flow in the stator windings. Stepper motor speeds are typically from zero to a few hundred RPM, and they are best suited to low speed applications Naturally, a stepper motor physically like the one shown would not be very useful as only large angles of rotation (45 degrees or multiples of this) could be obtained unless gearing was used. Real world stepping motors have toothed rotors that often will resemble a gear, 48 or more discrete steps, with usually 200 or sometimes 400 steps. This allows 1.8 degree or 0.9 degree increments respectively, or even smaller by using half or mini stepping methods. Common stepper motors are usually two or four phase, depending on the number of windings on the stator. Usually there are two or four, and often the windings may be connected internally, to reduce the number of external leads. This is often done with the ground connections. All stepper motors will have at 52

least two phases, with four commonly used. There are also six phase stepper motors available. There are 3 basic types of stepper motors. The VR (variable reluctance) type has a soft iron rotor and can be turned when de-energized, since there is no holding torque. The PM (Permanent magnet type has a radially magnetized rotor. This type has detents when deenergized, which may present a problem in some applications. It is not suitable for small step angles. The hybrid type has an axially polarized rotor with sections, one with all north poles, the other with all south poles, and is a combination of the VR and PM type. The hybrid and variable reluctance types are the most commonly used.

5.3 Phases, Poles and Stepping Angles Usually stepper motors have two phases, but three- and five-phase motors also exist. A bipolar motor with two phases has one winding/phase and a unipolar motor has one winding, with a center tap per phase. Sometimes the unipolar stepper motor is referred to as a “four phase motor”, even though it only has two phases. Motors that have two separate windings per phase also exist—these can be driven in either bipolar or unipolar mode. A pole can be defined as one of the regions in a magnetized body where the magnetic flux density is concentrated. Both the rotor and the stator of a step motor have poles. In reality several more poles are added to both the rotor and stator structure in order to In Full Step Drive you are energizing two phases at any given time. The stator is energized according to the sequence AB AB AB  AB and the rotor steps from position 1 3 5 7 . Full step mode results in the same angular movement as 1 phase on drive but the mechanical position is offset by one half of a full step. The torque output of the unipolar wound motor is lower than the bipolar motor (for motors with the same winding parameters) since the unipolar motor uses only 50% of the available winding while the bipolar motor uses the entire winding. 

5.4 Experimental Results In this section the real-time results of the stepping control of the motor is presented. In hardware, first of all drive the stepper motor through a micro-stepping technique, where applying the inputs of sine and cosine to the drive circuitry. So the stepper motor stepping sequence follows that form of input. In this experiment , digital count values can find from the anaput and use that digital count as two winding current inputs to the stepper motor that the implementation. The IC 555 timer which is biased by IC 7805 s to give the sequential pulses that 53

would be used for rotating the stepper motor. IC 7805 gives 5V for biasing every IC s . The motor starts rotating when IC SN74194 takes pulse from IC 555 timer . There are two switching transistor used for controlling the direction of the speed of the stepper motor. When Q1 is on it is rotating as like the clockwise direction, for Q2 it is rotating anticlockwise. A switch is used to turn on and turn off these transistors. The speed can be varied using potentiometer. For increasing the resistance of the potentiometer the motor rotates slowly and it rotates fast with decreasing the resistance of potentiometer. For disconnecting between IC 555 timer and SN 74194 the motor is stopped , because in this time SN 74194 does not take any pulses from IC 555 timer. Moreover rotating of the stepper motor can be stopped by switch.

In this work we have got some results,Stepper motors differ from standard DC motors in that they do not spin freely when power is applied.For a stepper motor to rotate, the power source must be continuously pulsed in specific patterns.The step sequence (pattern) determines the direction of the stepper’s rotation. The time between sequence steps determines the rotational speed. Each step causes the stepper motor to rotate a fixed angular increment. The stepper motor supplied with the StampWorks kit rotates 3.6 degrees per step. This means that one full rotation (360 degrees) of the stepper requires 100 steps.The step sequences for the motor are stored in DATA statements. The StepFwd subroutine will read the next sequence from the table to be applied to the coils. The StepRev subroutine is identicalexcept that it will read the previous step.By adding the maximum value of the sequence to the current value.

5.5 Summary

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Chapter 6

Discussions and Conclusions

6.1 Discussions The circuit is designed to drive stepper motors and provides only basic control functions Forward, Reverse, Stop and Speed adjustment. The circuit is not complex and is cheaper than many dedicated driver/controller devices and the parts are easy to find. During the setup of the stepper motor driver circuit, it was observed that the IC SN74194 would burn out immediately after the switch has been turned on. Later, it has discovered that the voltage regulator circuit LM 7805 was not installed with the correct polarity. View to this incorrect polarity, a voltage must higher than the desired 5 volt level was delivered to the 16, 1, 3 pins of IC SN74194. As a result the IC will get heated up as a consequence it would burned out easily. On the other hand, the bi-directional switch was shorted internally. So the stepper motor was connected to rotted in only one direction. Later both the IC and the switch was properly installed and the entire circuit worked as expected.

6.2 Suggestions of future work As for the future work, first of all it can implement the technique using a faster microcontroller or DSP. For example, we can use a micro-controller which is specifically designed for motor control applications. It can also implement the fuzzy control technique, neural network control, active disturbance rejection control, or other optimized control techniques to control the motor speed. Another option would be to implement particle filters or other non-linear filter techniques to estimate the winding currents. Finally, it could be implement by switching to hardware based filtering, or a faster micro-controller or DSP.

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This circuit also can be used as pwm controller with variation of time period.

6.3 Limitations of this circuit This application note describes how to implement an exact linear speed controller for stepper motors. The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation. Many advantages are achieved using this kind of motors, such as higher simplicity, since no brushes or s are present, low cost, high reliability, high torque at low speeds, and high accuracy of motion. Many systems with stepper motors need to control the acceleration/ deceleration when changing the speed. This note presents a driver application capable of controlling acceleration and speed. The two common types of stepper motors are the bipolar motor and the unipolar motor. The bipolar and unipolar motors are similar, except that the unipolar has a center tap on each winding. The bipolar motor needs current to be driven in both directions through the windings, and a full bridge driver is needed. The center tap on the unipolar motor allows a simpler driving circuit, limiting the current flow to one direction. The main drawback with the unipolar motor is the limited capability to energize all windings at any time, resulting in a lower torque compared to the bipolar motor. The unipolar stepper motor can be used as a bipolar motor by disconnecting the center tap. Full vs. half stepping Stepper motors used in full-stepping mode powers one winding at a time. This way, four different settings (positions) is possible. By powering both windings simultaneous, the stepper motor is trapped between the positions obtained when full-stepping, also known as half-stepping. This gives the eight positions. When powering both windings, the torque is approximately 1.4 times higher than when powering only one winding, but at the cost of twice the power consumption.

Speed properties One drawback with the stepper motor is the limited torque capabilities at high speeds, since the torque of a stepper motor will decrease with increasing speed. The torque also drops at the resonant speed. The resonant speed will depend on the driving scheme of the stepper motor and the load. Maximum torque is achieved at low speeds, and this is an advantageous in many applications. 56

Fundamental of rotational motion To create rotational motion in a stepper motor, the current through the windings must change in the correct order. This is obtained using a driver that gives the correct output sequence when subjected to a pulse (‘stepper motor pulse’) and a direction signal. To rotate the stepper motor at a constant speed, pulses must be generated at a steady rate.

Linear speed ramp To start and stop the stepper motor in a smooth way, control of the acceleration and deceleration is needed. Using a constant acceleration/deceleration gives a linear speed profile. The time delay between the stepper motor pulses controls the speed. These time delays must be calculated in order to make the speed of the stepper motor follow the speed ramp as closely as possible. Discrete steps control the stepper motor motion, and the resolution of the time delay between these steps is given by the frequency of the timer.

6.4 Conclusions The applications of permanent magnet stepper motors have grown significantly in recent years in the appliance industry and the automotive industry, among others. These motors are used in a variety of industries, including high and low propulsion technology, computer peripherals, machine tools, robotics, etc. Sensor less permanent magnet motors are preferable to encoder-based systems because of compactness, low cost, low maintenance, and high reliability. The conventional sensor less method based on a neutral motor point has limited application since it has a low speed range, suffers from high common mode voltage noise, and exhibits high frequency switching noise. In this thesis, we explore a technique where we measure the current through a sense resistor and use it to estimate the speed and position of the stepper motor using its mathematical model. We used different kinds

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of techniques to estimate the speed and position to achieve speed control and then tried to implement it in hardware. First of all, using the mathematical model of the stepper motor, we performed a steady state analysis of the system. After that we implemented the discrete time extended in the simulation and the results were good compared to the other approaches, because we used a pure discrete time model by partially differentiating the system model matrix. The next task of the thesis was to implement the extended filter in the Microchip. Before implementing. So we generated the sine and cosine input using the varying duty-cycle of a PWM. After that we used the motor driver chip and other peripheral circuitry to drive the motor. Next we measured the current waveform of the voltage across the sense resistor and applied it to the anaput. The equivalent digital value of the analog signal is used to update the measurement equation. While implementing the whole system throughput time became too large compared to the required sampling time to update the measurement and time equations. Because of that reason the overall system becomes unstable in hardware and could not achieve the estimate of speed and position using the given information.

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Appendix Control Using XILLIX Software It can be used by XILLINX(verson 5.1) software which code is following VHDL CODE: library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; -- Uncomment the following lines to use the declarations that are -- provided for instantiating Xilinx primitive components. --library UNISIM; --use UNISIM.VComponents.all; entity motor_control is Port ( ready : out std_logic; go : in std_logic; dac : in std_logic; clock : in std_logic; seed : in std_logic_vector(9 downto 0); spd_con : in std_logic_vector(9 downto 0); motor_out : out std_logic); end motor_control; architecture Behavioral of motor_control is signal ld_sd, en_ran, zero_cross, spd_con_gt_eq_ran, motor_on: std_logic; signal ran_num,spd_con_reg:std_logic_vector(9 downto 0); signal n_s,p_s:std_logic_vector(1 downto 0); begin --NSOL process(p_s, go, dac, spd_con_gt_eq_ran) begin ld_sd<='0';en_ran<='0';zero_cross<='0';motor_on<='0'; case p_s is 59

when "00" => ready<='1'; if (go='1')then ld_sd<='1';n_s<="01"; else n_s<="00"; end if; when "01" => en_ran<='1'; if(dac='1')then n_s<="01"; else zero_cross<='1'; if (spd_con_gt_eq_ran='1')then motor_on<='1';n_s<="10"; else n_s<="10"; end if; end if; when "10" => en_ran<='1'; if(dac='0')then n_s<="10"; else zero_cross<='1'; if(spd_con_gt_eq_ran='1')then motor_on<='1'; n_s<="01"; else n_s<="01"; end if; end if; when others => n_s<="00"; end case; end process; --PSR process(clock) begin if rising_edge(clock) then p_s<= n_s; end if; end process; process(clock) begin if rising_edge(clock) then spd_con_reg<= spd_con; end if; end process; process(clock) begin if rising_edge (clock) then if (ld_sd='1') then ran_num<= seed; elsif (en_ran='1') then ran_num<=ran_num(8 downto 0) & (ran_num(2) xor ran_num(0)); end if; end if; end process;

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process(clock) begin if rising_edge (clock) then if (zero_cross='1') then motor_out<= motor_on; end if; end if; end process; process(spd_con_reg, ran_num) begin if (spd_con_reg > ran_num) then spd_con_gt_eq_ran<='1'; elsif (spd_con_reg = ran_num) then spd_con_gt_eq_ran<='1'; elsif (spd_con_reg < ran_num) then spd_con_gt_eq_ran<='0'; else spd_con_gt_eq_ran<='0'; end if; end process; end Behavioral;

TESTBENCH: -- VHDL Test Bench Created from source file motor_control.vhd -- 16:01:20 07/27/2009 --- Notes: -- This testbench has been automatically generated using types std_logic and -- std_logic_vector for the ports of the unit under test. Xilinx recommends -- that these types always be used for the top-level I/O of a design in order -- to guarantee that the testbench will bind correctly to the post-implementation -- simulation model. -LIBRARY ieee; USE ieee.std_logic_1164.ALL; USE ieee.numeric_std.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; ENTITY testbench IS END testbench; ARCHITECTURE behavior OF testbench IS COMPONENT motor_control 61

PORT( go : IN std_logic; dac : IN std_logic; clock : IN std_logic; seed : IN std_logic_vector(9 downto 0); spd_con : IN std_logic_vector(9 downto 0); ready : OUT std_logic; motor_out : OUT std_logic ); END COMPONENT; SIGNAL ready : std_logic; SIGNAL go : std_logic:='0'; SIGNAL dac : std_logic:='0'; SIGNAL clock : std_logic:='0'; SIGNAL seed : std_logic_vector(9 downto 0):="0000000001"; SIGNAL spd_con : std_logic_vector(9 downto 0):="0000111111"; SIGNAL motor_out : std_logic; BEGIN uut: motor_control PORT MAP( ready => ready, go => go, dac => dac, clock => clock, seed => seed, spd_con => spd_con, motor_out => motor_out ); -- *** Test Bench - Defined Section *** clock<= not clock after 50 ns; go<= '1' after 230 ns; dac<= not dac after 280 ns; -- *** End Test Bench - Defined Section *** END; In this chapter, the implementation of the circuit that can be used for controlling speed of the stepper motor has been discussed. The operation of this circuit , and controlling this circuit using XILLIX software have been explained. From this chapter, devices ( IC s , 62

resistors , capacitors ) which are connected with another device, their function also can be learned.

References 1. Robert L. Boylestad , “ Introductory Circuit Analysis “ Tenth Edition PrenticeHall of India , pp. Chapter 1 and Chapter 2.. 2. Robert L. Boylestad , “ Electronic Devices and Circuit Theory “ , Ninth Edition Prentice-Hall of India .. 3. Robert F. Coughlin , “ Operational Amplifiers and Linear Integrated Circuits” , Sixth Edition pp. Chapter 6 and Chapter 7 . 4. Charles A. Schuler and William L. Mcnamee, “ Industrial Electronics and Robotics “ , Sixth Edition 5. Jacob Millman and Christos C. Halkias , “ Electronic Devices and Circuit “ , Fifth Edition , Prentice-Hall of India , pp. Chapter 1 and Chapter 2.. 6. B.L.Thereja , “ Electrical Machines “ 10th Edition , Prentice-Hall of India , pp. synchronous motors 7. Motors for http://en.wikipedia.org/wiki/Motors page no 1, 2, 3 8. Some devices for http://en.wikipedia.org/wiki/Devices 9. Transistors and IC s for http://en.wikipedia.org/wiki/ICs detector pares 10. Xillinx Software

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