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|Title:||Robot Sürüşü İçin Doğrusal Asenkron Motor Tasarımı|
|Other Titles:||Design of linear induction motor as a robot actuator|
|Publisher:||Fen Bilimleri Enstitüsü|
Institute of Science and Technology
|Abstract:||Son yıllarda oldukça ilerleme gösteren denetim yöntemleri, bilgisayar etkisi, malzeme teknolojisinin ilerlemesi gibi etkenler öteki endüstri uygulamalarını ele geçirmiş olan asenkron motoru robot uygulaması için de çekici duruma getirmiştir. Tezde, daha da özel bir durum ele alınarak, doğrusal tubular türde çelik ikinci İli bir asenkron motorun robot sürücüsü olarak kullanılma araştırılması yapılmıştır. Araştırma yapılırken tümüyle kuramsal kalınmamış, bir deney motorunun tasarlanıp gerçekleştirilmesiyle bu tür motorların robot sürücüsü olarak uygunluk derecesi saptanmıştır. Sonuçlar yüksek düzeyde olumludur. Motorun bir kuvvet makinesi olması, durma çalışması yapabilmesi verdiği öteleme kuvvetinin denetiminin yapıla bilmesi, kuvvet/hız özeğrisinin her noktada kararlı oluşu robotlar için gerçekten olumlu özelliklerdir. Yapısal olarak en büyük sorun ısınmadır. Ancak bu tür motorlar, büyük ikincil yüzeyleri nedeniyle etkili soğutmaya elverişlidirler. Buna dayanarak, bu sakıncanın ortadan kaldırılabileceği anlaşılır. Konum denetimi açısından da vektör denetiminin geliştirilmesiyle A. A. motorlarının özgüllükleri D. A. motorununkine benzer ve bu tür motorlar için eski sakıncaların ortadan kalkmasına yol açar. Tezde; anlaşılabilir olması açısından önce gü nümüz robotlarındaki elektriksel sürüş kapsamlı olarak verilmiş ve bu bilgilerin üzerine doğrusal çelik ikincilli asenkron motor kuramı ve uygulaması eklenerek, robotlardaki elektriksel sürüş dizgelerinin neler olduğu ve neler olabileceği konusunda bir yerlere varılması amaçlanmıştır. Tasarım ve deney ayrıntılı olarak verilmiştir. Daha sonra çelik ikincilli doğrusal asenkron motorun yalın de netlenme özellikleri incelenerek denetim sorununa getireceği yenilikler göz önüne alınmıştır.|
Basic Concepts of Robotics Above all, that question must be answered: What is a robot? Several definitions of robots are exist: - The popular conception is of a mechanical man capable of carrying out tasks that a human might do and displaying some capability for intelligence. Robots are often portrayed in movies as strong and stupid. More recent movies such as Star Wars have shown friendly, capable robots such as C3P0 and R2D2 who worked with their human counterparts in fighting the empire. - Users and manufacturers of industrial robots have banded together to form tne Robot Institute of America. They have a suitably precise definition: " A robot is a reprogrammable, multifunctional ma nipulator designed to move material parts, tools or specialized devices through variable programmed mo tions for the performance of variety of tasks." Other useful ways of defining robots are exist. Main problem of robots is control. There are several ways of control: - Point-to-point robots: These robots are able to move from one specified point to another but can not stop at arbitrary points not previously design ated. They are simplest and least expensive type of robots. Stopping points are often ^ust mechani cal stops that must be adjusted for each now opera tion. Point-to-point robots driven by servos are often controlled by potentiometers set to stop the robot arm at a specified point. - Continous path robots: These robots are able to stop at any specified number of points along a path. However, if no stop is specified, they may not s t ay on a straight line or constant curved pa th between specified points. Every point must be -vi- stored separately in the memory of the robot. - Controlled path (computed trajectory) robots: Control equipment on controlled path robots can ge nerate straight lines, circles, interpolated curves and other parts with high accuracy. Paths can be specified in geometric or algebraic terms in some of these robots. Good accuracy can be obtained at any point along the path. Only the start and fi nish coordinates and the path definition are requi red for control. - Servo versus non-servo robots: Servo contro lled robots have some means for sensing their posi tion and "feeding back" the sensed position to the means of control in such a way that the control, can cause a particular path to be followed. Non-servo robots have no way of determining whether or not they have reached a specified location. Controlled path robots all have servo capabi lity so that they can correct their path constantly to carry out a specified motion. 2) Electrical Drive In Robots Electrical drive is dominant method of drive in robotics. Also it is a proper driving method for future robots. Sooner or later electrical machines will capture all robot driving systems. Most people are more familiar with electric po wer than with fluid power, since the former is com mon in every household and in most walks of life. With respect to robot applications, electric power offers several advantages:, - Electric actuators are easy to control: they can provide fast accurate control of position and speed. - They are readily available and inexpensive. - It is easier to design for wiring than piping. - Electric actuators are quiet in operation. - Electrical systems are clean. - Electrical systems are improvable. -vii- But again, as in all areas of technology, the re are disadvantages to be considered: - Power/weight and torque/weight ratios are low. - Low torques require extensive gearing and be cause öf backlash this can introduce control prob lems. - Arcing can cause a fire hazard: up to recently electric actuators was therefore eliminated from certain tasks such as paint spraying. But A..C. in duction motors (with cage or core rotor) have eli minated that avoidance. - The possibility of electric shock introduces a safety hazard. Electric motor drives must have individual controls capable of controlling the power for reli able and unexpensive drives. In large robots, this requires switching of 10 to 50 A at 20 to 100 V. Small electric motors use simple switching circuits and are easy to control with low power circuits. There are three main types of electrical actu ators: D.C. motors, stepper motors and A.C. servomo tors. The operation of the D.C. motor relies on the fact that a conductor in a magnetic field at right angles to it experiences a force perpendicular to the current and the magnetic lines of force. The magnetic field is created by permanent magnets or field windings in stator and is radial. The rotor carries the armature windings, which lie axially, so that the force created when current flows thro ugh the armature causes the rotor to turn. Precise control of positioning in D.C. motors requires that a closed-loop servo be used with some type of positional feedback. Because of the closed loop control, the smooth operation possible, and the ability to generate large torques, D.C. motors are used in those robots in which precise control and high power are required. Stepper motors are a unique type of actuator and have been used mostly in computer peripherals. A stepper motor provides output in the form of -viii- discrete angular motion increments. It is actuated by a series of discrete electrical pulses. For eve ry electrical impulse there is a single-step rotati on of the motor shaft. In robotics, stepper motors are used for relatively light duty applications. Also, stepper motors are typically used in open lo op systems. There are numerous other aspects of electric motors which maybe investigated. Recent advances in control electronics are producing A. C. servomo tors. These motors have the advantages of being cheaper to manufacture than D.C. motors, they have no brushes, and they possess a high power output With the proper electronics package, however, their performance can be made to look very much like the performance of a D.C. motor. 3) Linear Induction Motort Design and Construc tion Linear Induction motor is a different type of electric machine. By an imaginary process, a rotary induction motor can be transformed into a linear in duction motor if the stator of rotary motor is cut by a radial plane and unrolled and the rotor is re placed by conducting sheet (or plate). This is not only for induction motor but also for. every type of electrical machines. It is designated the "stator" as the "primary" and the "rotor" as the "secondary". Notice that the primary (core and windings) now has a finite length, called active length of the linear induction machine, and it has a beginning and an end. The presence of these two ends leads to the phenomenon of end effects (or edge effects) which is unique to linear induction machines and does not exist in conventional rotating machines. Such motors are obviously "flat" linear induc tion motors. If the flat primary is rerolled about an axis parallel to the direction of the field moti on, an entirely different form of cylindirical stru cture is produced, and the field now travels along the bore of primary. Such motors are tubular motors or axial flux motors. One obvious advantage of a tubular motor is that it does not have any end con nections. There are a number of ways in which a tubular motor maybe wound. Linear induction machine can be operated as a force machine which operates at very low speeds -ix- or at standstill mode. These machines are called as force machines because of obtaining maximum force at zero speed. Efficiency is not a good reference frame from which to judge the usefulness of these linear machi nes, since at standstill the power output is zero. Therefore, an introduction of the goodness factor is desirable so as to have some means of measuring the ability of a machine to convert or transform electrical power into mechanical force. For motors designed for continous high-speed operation, effici ency and power factor should be high. On the other hand, for low speed or standstill operation, atten tion should be directed towards other measures of performance such as the ratios force/input power, force/stator copper loss and force/weight. Designed and constructed motor in this thesis is a. tubular motor with steel secondary. It is a experimental motor. Its nominal values are: 380 V terminal voltage (3 phases), 50 Hz frequency, 7.5 m/s synchron speed. For different terminal volta ges, varying performance values were obtained by using an experimental system. Design calculations are made with respect to "Generalized nonlinear the ory". By using experimental and calculated values, performance char as t eri s tics of the motor are obtai ned. Differences between experimental and calcula ted values are acceptable. Thus, calculating met hod is succesful. 4) Controlling Features of Linear Induction Motor with Solid-Steel Secondary. In general terms, induction motors with solid steel secondary have higher secondary resistance than those containning high-conductivity material. Consequently, their force/speed characteristics are different to those of conventional induction motors. Thus, they produce high force at stand still and the force reduces with increase in speed. Their force-speed curve is then stable over the full range of motoring speeds. Starting current is relatively low and the entrefer is small, com pared with linear motors with conducting-plate secondary, so magnatising current is reduced. The. power factor is also higher, except at low slips. In addition, steel secondaries are robust rigid and have good thermal properties. -x- These features are appropriate for control. Speed control could be done by only changing the terminal voltage. Force/speed characteristics are stable at every point. 5) Using The Linear Motors For Linear Motion of Robot Linear motion is often used due to mechanical structure in robots. Linear joints have good accu racy and stiffness.. For linear motion, it is used mechanical transmission or fluid or pneumatic cylin ders. So linear induction motor can be used in robo tics. Especially Linear induction motor with steel secondary is very proper for robots. Above all it is a "force" machine, it can be operated at stand still mode and it can be controlled at every charac teristic point. These are attractive properties for robots. 6) Control of Robots The function of a robot is to perform useful tasks without a means of controlling the movements of manipulator. It is essential to use closed loop control, in which the error between a desired and an actual variable is used for corrective purposes». Control of a robot arm involves an extremely diffi cult analytical task. The dynamics of a robot with n degrees of freedom are highly non-linear: they are described by a set of n highly coupled, non-linear, second order differantial equations. The non-linea rities arise from inertial loading, from coupling between adjacent links of the manipulator and from gravity loads. In any control system it is important to know precisely the desired value of the controlled vari able. Where robots are taught by pendant or lead through, the desired values of each machine coordi nate are recorded. during teaching. 7) Induction Motors for Position Servomecha- nisms. Vector control enables the induction motor flux and torque to be controlled independently! thus the induction motor reveals control characteristics of D.C. motor and can be employed as the actuator in positioning s ervome onanisms.
|Description:||Thesis (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1992|
Tez (M.Sc. ) -- İstanbul Technical University, Institute of Science and Technology, 1992
|Appears in Collections:||Elektrik Mühendisliği Lisansüstü Programı - Yüksek Lisans|
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