Brode makinasında performans artışı için çerçeve hareket hızının artırılması ve hareket kontrolü

Abstract

Bu çalışma Saurer 3040 model 21 Yard uzunluğundaki brode makinası baz alınarak yapılmıştır. Birinci bölümde nakış ve nakısın tarihi kısaca anlatılmış teknolojik gelişmelerden bahsedilmiştir. Ayrıca bu çalışmada makina performansı için hedeflenen değerler belirtilmiştir. İkinci bölümde brode makinasının tanıtılmasına yönelik detaylar belirtilmiş, makinanın çalışma felsefesi anlatılmaya çalışılmıştır. Bölüm üç brode makinası çerçeve hareketinin hangi hız profili ile yaptırılacağına ilişkin hareket incelemesini içerir. Dördüncü bölümde motor seçimi, matematik modelin kurulması ve çeşitli kontrol algoritmalarının uygulanması detaylı bir biçimde sunulmuştur. Bu çalışmaların sonuçlan beşinci bölümde verilmiştir. Son olarak bölüm altı, bu çalışmanın sınırlarının belirtildiği ve bu konuda daha neler yapılabileceğinin önerildiği bölümdür.

Embroidery is an embellishment which is applied to a surface (cotton, silk, leather, etc) by using a needle and yarn. There are two type of embroidery machines in the market, multi head and long type. In long type embroidery machines mostly curtain is embroideried. In those machines embroideried surface is in vertical position. Embroidery was made by hand until the year 1860. As a result of this, embroideries were very expensive and not widely used. First shuttle embroidery machine was discovered by Franz Saurer, Switzerland in 1 869. Standart lengths of the long type machines are 5, 10, 15, 21 Yards. Bigger machine length means slower speed so less stitch. Because the machines are so expensive amortization period is not less than 3 years depending on cost and labour. At this point, even little increment of performance may provide big advantages in costs and competition. This study covers Saurer 3040-21 Yards long type embroidery machine. There are 1416 needles on that machine and it runs up to 185 rpm. Total weight is 27 t and frame weight is about 1500 kg. Machine is driven by a main motor, X/Y frame motors and a coulisse motor. Loop formation: The needle is in the first low position before formation of the loop. In this moment, the shuttles are still in their lowest position. Then the needle comes back a little. The shuttle point seizes the thread behind the eye of the needle. After that, the needle goes to the lowest position again and the shuttle pushed through the loop. Last, the needle is in its initial position and the shuttle in its highest position. Thread system pentamat includes bobbin (supplies thread), thread brake (adjust thread tension), big and small thread guides, needle, borer and shuttle. Main drive shaft drives cams of needle, big and small thread guides, borer, fabric presser and shuttle mechanisms. Frame weight is balanced by a helical spring at the end of the machine when the machine first initialized. Frame motion is obtained by servo motors controlled individually in horizontal (X) and vertical (Y) direction each. Machine is driven from one end. Cams get the motion from main shaft and transmit it to the last action shafts which are situated whole length of machine. For each standart machine length, recommended speed values are can not be increased. Otherwise vibration increase dramatically on last action shafts and breakdown may occur in cam mechanisms. Recommended machine speed is 185 rpm for 14mm stitch length in Saurer 3040- 21. In this study, frame motion is isolated from all other parts and supposed to reach higher values in order to obtain better performance. Frame does not move in the 0-230 degree range of main shaft. In this period, needles and shuttles are driven. After 230 degree, frame start to move to reach the next stitch coordinates and it stops at 360 degree. If the machine runs at 185 rpm the frame motion has to be done in 117ms. Target speed in this study is 309 rpm and so frame motion period is 70ms. Two trigonometric and one parabolic speed profiles has been examined and below speed profile is choosen. co = ( L / 0.07 ) * [ 1 - cos ( 2irt / 0.07 ) ] Here, L is stitch length and t is the time changing from 0 to 0.07 seconds. The most common structure for high performance motion controllers consist position controller, velocity controller and current controller. This cascade control structure has an innermost current loop, a velocity loop around the current loop and a position loop around the velocity loop. This multiloop control structure functions properly only if the bandwidth of the loops have the proper relationship. Bandwidth is the measure of how well the controlled quantity tracks and responds to the command signal. The current loop must have the highest bandwidth, the velocity loop and finally the position loop has the lowest bandwidth. Therefore, the tunning of the control-loop regulators is accomplished by starting with the innermost loop and working outward. PI control has been performed in this study for current loop. One limitation of the current loop is gain, phase and offset errors that occur due to imperfect sensors and other circuitry. These errors are one source of torque ripple so it is important to keep these errors to an absolute minimum. Another limitation of the properly designed current controller is insufficient voltage to generate the necessary current. This situation occurs for large value current commands at higher motor speeds when the back EMF of the motor begins to approach the motor supply voltage. The most common velocity controller structure is the PI regulator. The choice of the P gain and the I gain for the desired response is made based upon the application requirements. Proportional gain is always used with higher bandwidths resulting from higher P gain values. The integral gain provides "stiffness" to load torque disturbances and reduces the steady-state velocity error to a zero value. However, integral gain does add phase shift to the velocity controller closed-loop frequency response and can result in a longer settling time. Therefore, a low value or zero value integral gain is sometimes used with very high bandwidth position controllers in point-to-point positioning applications while a significant integral gain value is used with contouring applications to provide high stiffness. In practice, usually tunning is done by trial-and-error techniques with the motor connected to the load or simulated load. Position control applications typically fall into two basic categories, contouring and point-to-point. P-to-P positioning is concerned about move time, settling time and velocity profile. The function of the motor in serving as the actuating component for the system is to provide the torque needed to accomplish the system's incremental motion demands. There are other devices available which are designed specifically to accomplish incremental motion functions, such as step motors. In those types a XI given motion command will result in a predetermined motion step. The DC motor has no such features and in order to function in an incremental motion servo system, it must be included in a control loop consisting of shaft connected transducers and amplifiers to control the motion. The DC motors offer superior response and improved flexibility in step rates and step sizes compared to the step motor: It turns out that the DC motor is used where the inherent limitations of step motors begin to be dominant. Some classes of DC motors are more suitable for incremental motion purposes than others. DC motors can be divided into several broad categories on the method they employ to create the magnetic field, and on the basic design and structure of the armature. Two basic classes of magnetic flux supply are the variable-magnetic- flux motors and the constant-magnetic-flux motors. Also three basic classes of armature design are the iron-core dc, the surface-wound dc and the moving coil motor. Also brushless dc motor should be considered as a special class which uses the same technology as the brush-type dc motors with the exception that the commutation is performed by electronic rather than mechanical means. Some primary performance characteristics required of the dc motor in order to meet the demands of incremental motion applications are; - Motor efficiency - Armature inertia - Armature inductance Linear current-to-torque relationships - Reluctance torque disturbance - The motor torque constant versus temperature - Motor peak current capability - Viscous damping coefficent - Torsional resonance conditions In chapter 4 all those points are examined and two control algorithms are performed; cascad control and linear quadratic optimum control. In cascad control, as previously discussed, three control loops were examined. Control signal is obtained by a correction term around reference control command. This correction term consists a current component which is the fastest loop, velocity component and position component which is the slowest. According to PD control algorithm, positional correction term is obtained from position and velocity output of system. Velocity correction term is obtained by PI control of only velocity output of system. Finally, PI control loop defined as current correction term which has positional and velocity correction terms. Xll Control loop frequencies can be calculated from differential equations of each control loops, easily. Details are in chapter 4.3. Another alternative control system, Linear Quadratic Optimum Control, is basically solution of the equation below; J = ( 1/2 ) J ( XTQX + UTRU ) dt Here, X is state variable matrix and U is command matrix. Matrixes R and Q are constant. Output matrix, U, is result of multiplying of state variable matrix, X, and coefficent matrix, K. K = - R"1BTP P matrix is obtained as solution of Riccati equation which is; -P = PA + ATP - PBR"1BTP + Q Solution of this expression gives equations which consist some unknown terms. Q and R matrixes can be defined. Thus we have only P matrix unknown. From this point, reverse integration is applied to the equations by using Runga-Kutta IV integration algorithm. Chapter 4.4 has all those calculations. Finally, point-to-point control is applied by using those control algorithms at the end of study. An embroidery design software is created for this aim. In this software a quarter circle is drawn as an example and saved as text file. Main computer program reads this file and calculates movements ( stitch length ) on x-axis and y- axis. For each movements, program calculates trajectories, applies choosen control algorithm. Block diagram of the system is as below; Hll XIV