A Hybrid Controller for Stability Robustness, Performance Robustness, and Disturbance Attenuation of a Maglev System

Devices using magnetic levitation (maglev) offer the potential for friction-free, high-speed, and high-precision operation. Applications include frictionless bearings, high-speed ground transportation systems, wafer distribution systems, high-precision positioning stages, and vibration isolation tables. Maglev systems rely on feedback controllers to maintain stable levitation. Designing such feedback controllers is challenging since mathematically the electromagnetic force is nonlinear and there is no local minimum point on the levitating force function. As a result, maglev systems are open-loop unstable. Additionally, maglev systems experience disturbances and system parameter variations (uncertainties) during operation. A successful controller design for maglev system guarantees stability during levitating despite system nonlinearity, and desirable system performance despite disturbances and system uncertainties. This research investigates five controllers that can achieve stable levitation: PD, PID, lead, model reference control, and LQR/LQG. It proposes an acceleration feedback controller (AFC) design that attenuates disturbance on a maglev system with a PD controller. This research proposes three robust controllers, QFT, Hinf , and QFT/Hinf , followed by a novel AFC-enhanced QFT/Hinf (AQH) controller. The AQH controller allows system robustness and disturbance attenuation to be achieved in one controller design. The controller designs are validated through simulations and experiments. In this research, the disturbances are represented by force disturbances on the levitated object, and the system uncertainties are represented by parameter variations. The experiments are conducted on a 1 DOF maglev testbed, with system performance including stability, disturbance rejection, and robustness being evaluated. Experiments show that the tested controllers can maintain stable levitation. Disturbance attenuation is achieved with the AFC. The robust controllers, QFT, Hinf , QFT/ Hinf, and AQH successfully guarantee system robustness. In addition, AQH controller provides the maglev system with a disturbance attenuation feature. The contributions of this research are the design and implementation of the acceleration feedback controller, the QFT/ Hinf , and the AQH controller. Disturbance attenuation and system robustness are achieved with these controllers. The controllers developed in this research are applicable to similar maglev systems

Penerapan Metode Kendali Nonlinier Berbasis Sistem Servo pada Sistem Magnetic Levitation (Maglev)

Dalam mendesain sistem kendali maglev umumnya terkendala oleh dinamika sistem yang kompleks dan nonlinier sehingga dibutuhkan pemilihan metode yang tepat. Oleh karena itu, pada penelitian ini diajukan sebuah pemodelan sistem kendali  maglev dengan menerapkan salah satu metode nonlinier yaitu feedback linearization yang dikembangkan dengan mengadaptasi sistem servo yang dinamakan kendali servo-feedback linearization. Hasil pemodelan sistem diuji dengan simulasi menggunakan matlab simulink. Performa sistem kendali hasil pemodelan yang diajukan pada penelitian ini dibandingkan dengan performa kendali feedback linearization sederhana. Hasil simulasi sistem kendali dengan skenario tanpa pemberian gangguan (disturbance) menunjukkan kendali feedback linearization dan kendali servo-feedback linearization menunjukkan performa yang bagus. Sinyal output kedua sistem kendali dapat mengikuti sinyal input referensi (set point). Hasil simulasi sistem kendali dengan skenario dengan penambahan gangguan (disturbance) dalam bentuk sinyal step menunjukkan kendali feedback linearization memiliki performa yang kurang baik, kendali tersebut tidak dapat meredam gangguan, sebaliknya kendali servo-feedback linearization dapat meredam gangguan yang diberikan

Third International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Third International Symposium on Magnetic Suspension Technology was held at the Holiday Inn Capital Plaza in Tallahassee, Florida on 13-15 Dec. 1995. The symposium included 19 sessions in which a total of 55 papers were presented. The technical sessions covered the areas of bearings, superconductivity, vibration isolation, maglev, controls, space applications, general applications, bearing/actuator design, modeling, precision applications, electromagnetic launch and hypersonic maglev, applications of superconductivity, and sensors

Design, Implementation and Control of a Magnetic Levitation Device

Magnetic levitation technology has shown a great deal of promise for micromanipulation tasks. Due to the lack of mechanical contact, magnetic levitation systems are free of problems caused by friction, wear, sealing and lubrication. These advantages have made magnetic levitation systems a great candidate for clean room applications. In this thesis, a new large gap magnetic levitation system is designed, developed and successfully tested. The system is capable of levitating a 6.5(gr) permanent magnet in 3D space with an air gap of approximately 50(cm) with the traveling range of 20x20x30 cubic millimeters. The overall positioning accuracy of the system is 60 micro meters. With the aid of finite elements method, an optimal geometry for the magnetic stator is proposed. Also, an energy optimization approach is utilized in the design of the electromagnets. In order to facilitate the design of various controllers for the system, a mathematical model of the magnetic force experienced by the levitated object is obtained. The dynamic magnetic force model is determined experimentally using frequency response system identification. The response of the system components including the power amplifiers, and position measurement system are also considered in the development of the force model. The force model is then employed in the controller design for the magnetic levitation device. Through a modular approach, the controller design for the 3D positioning system is started with the controller design for the vertical direction, i.e. z, and then followed by the controller design in the horizontal directions, i.e. x and y. For the vertical direction, several controllers such as PID, feed forward and feedback linearization are designed and their performances are compared. Also a control command conditioning method is introduced as a solution to increase the control performance and the results of the proposed controller are compared with the other designs. Experimental results showed that for the magnetic levitation system, the feedback linearization controller has the shortest settling time and is capable of reducing the positioning error to RMS value of 11.56μm. The force model was also utilized in the design of a model reference adaptive feedback linearization (MRAFL) controller for the z direction. For this case, the levitated object is a small microrobot equipped with a remote controlled gripper weighting approximately 28(gr). Experimental results showed that the MRAFL controller enables the micro-robot to pick up and transport a payload as heavy as 30% of its own weight without a considerable effect on its positioning accuracy. In the presence of the payload, the MRAFL controller resulted in a RMS positioning error of 8μm compared with 27.9μm of the regular feedback linearization controller. For the horizontal position control of the system, a mathematical formula for distributing the electric currents to the multiple electromagnets of the system was proposed and a PID control approach was implemented to control the position of the levitated object in the xy-plane. The control system was experimentally tested in tracking circular and spiral trajectories with overall positioning accuracy of 60μm. Also, a new mathematical approach is presented for the prediction of magnetic field distribution in the horizontal direction. The proposed approach is named the pivot point method and is capable of predicting the two dimensional position of the levitated object in a given vertical plane for an arbitrary current distribution in the electromagnets of the levitation system. Experimental results showed that the proposed method is capable of predicting the location of the levitated object with less than 10% error

Multi - objective sliding mode control of active magnetic bearing system

Active Magnetic Bearing (AMB) system is known to inherit many nonlinearity effects due to its rotor dynamic motion and the electromagnetic actuators which make the system highly nonlinear, coupled and open-loop unstable. The major nonlinearities that are associated with AMB system are gyroscopic effect, rotor mass imbalance and nonlinear electromagnetics in which the gyroscopics and imbalance are dependent to the rotational speed of the rotor. In order to provide satisfactory system performance for a wide range of system condition, active control is thus essential. The main concern of the thesis is the modeling of the nonlinear AMB system and synthesizing a robust control method based on Sliding Mode Control (SMC) technique such that the system can achieve robust performance under various system nonlinearities. The model of the AMB system is developed based on the integration of the rotor and electromagnetic dynamics which forms nonlinear time varying state equations that represent a reasonably close description of the actual system. Based on the known bound of the system parameters and state variables, the model is restructured to become a class of uncertain system by using a deterministic approach. In formulating the control algorithm to control the system, SMC theory is adapted which involves the formulation of the sliding surface and the control law such that the state trajectories are driven to the stable sliding manifold. The surface design involves the transformation of the system into a special canonical representation such that the sliding motion can be characterized by a convex representation of the desired system performances. Optimal Linear Quadratic (LQ) characteristics and regional pole-clustering of the closed-loop poles are designed to be the objectives to be fulfilled in the surface design where the formulation is represented as a set of Linear Matrix Inequality optimization problem. For the control law design, a new continuous SMC controller is proposed in which asymptotic convergence of the system’s state trajectories in finite time is guaranteed. This is achieved by adapting the equivalent control approach with the exponential decaying boundary layer technique. The newly designed sliding surface and control law form the complete Multi-objective SMC (MO-SMC) and the proposed algorithm is applied into the nonlinear AMB in which the results show that robust system performance is achieved for various system conditions. The findings also demonstrate that the MO-SMC gives better system response than the reported ideal SMC (I-SMC) and continuous SMC (C-SMC)

Design, Optimization, and Experimental Characterization of a Novel Magnetically Actuated Finger Micromanipulator

The ability of external magnetic fields to precisely control micromanipulator systems has received a great deal of attention from researchers in recent years due to its off-board power source. As these micromanipulators provide frictionless motion, and precise motion control, they have promising potential applications in many fields. Conversely, major drawbacks of electromagnetic micromanipulators, include a limited motion range compared to the micromanipulator volume, the inability to handle heavy payloads, and the need for a large drive unit compared to the size of the levitated object, and finally, a low ratio of the generated magnetic force to the micromanipulator weight. To overcome these limitations, we designed a novel electromagnetic finger micromanipulator that was adapted from the well-known spherical robot. The design and optimization procedures for building a three Degree of Freedoms (DOF) electromagnetic finger micromanipulator are firstly introduced. This finger micromanipulator has many potential applications, such as cell manipulation, and pick and place operations. The system consists of two main subsystems: a magnetic actuator, and an electromagnetic end-effector that is connected to the magnetic actuator by a needle. The magnetic actuator consists of four permanent magnets and four electromagnetic coils that work together to guide the micromanipulator finger in the xz plane. The electromagnetic end-effector consists of a rod shape permanent magnet that is aligned along the y axis and surrounded by an electromagnetic coil. The optimal configuration that maximizes the micromanipulator actuation force, and a closed form solution for micromanipulator magnetic actuation force are presented. The model is verified by measuring the interaction force between an electromagnet and a permanent magnet experimentally, and using Finite Element Methods (FEM) analysis. The results show an agreement between the model, the experiment, and the FEM results. The error difference between the FEM, experimental, and model data was 0.05 N. The micromanipulator can be remotely operated by transferring magnetic energy from outside, which means there is no mechanical contact between the actuator and the micromanipulator. Moreover, three control algorithms are designed in order to compute control input currents that are able to control the position of the end-effector in the x, y, and z axes. The proposed controllers are: PID controller, state-feedback controller, and adaptive controller. The experimental results show that the micromanipulator is able to track the desired trajectory with a steady-state error less than 10 µm for a payload free condition. Finally, the ability of the micromanipulator to pick-and-place unknown payloads is demonstrated. To achieve this objective, a robust model reference adaptive controller (MRAC) using the MIT rule for an adaptive mechanism to guide the micromanipulator in the workspace is implemented. The performance of the MRAC is compared with a standard PID controller and state-feedback controller. For the payload free condition, the experimental results show the ability of the micromanipulator to follow a desired motion trajectory in all control strategies with a root mean square error less than 0.2 mm. However, while there is payload variation, the PID controller response yields a non smooth motion with a large overshoot and undershoot. Similarly, the state-feedback controller suffers from variability of dynamics and disturbances due to the payload variation, which yields to non-smooth motion and large overshoot. The micromanipulator motion under the MRAC control scheme conversely follows the desired motion trajectory with the same accuracy. It is found that the micromanipulator can handle payloads up to 75 grams and it has a motion range of ∓ 15 mm in all axes

Modellazione e controllo di sistemi MagLev ellittici

Questa tesi è parte di un progetto più grande svolto in collaborazione con l'Università Norvegese di Scienze e Tecnologie, NTNU, che come obbiettivo ha l'idealizzazione di una piattaforma per la levitazione magnetica che sia economica e relativamente facile da assemblare. Gli studenti di teoria dei sistemi di controllo avrebbero dunque l'opportunità di replicare questa piattaforma per sperimentare i concetti teorici che hanno studiato e svilupparne una miglior comprensione. I primi passi del progetto sono stati compiuti da un gruppo di studenti del NTNU nella loro tesi triennale, "Magnetic levitation systems: design, prototyping and testing of a digital PID-controller”. Essi costruirono una piattaforma che sfrutta dei magneti permanenti per generare un campo magnetico stabile, dei solenoidi per alterare questo campo magnetico nel modo necessario per mantenere in equilibrio un disco magnetico, e un controllore PID per gestire questi solenoidi. Inoltre svilupparono anche un simulatore del sistema in MATLAB. In questa tesi è riportata parte della seconda iterazione di questo progetto, svolta in collaborazione con altri due studenti dell'Università degli Studi di Padova, Alberto Morselli e Andrea Nicetto. In questa seconda fase del progetto è stata compiuta una ri-pianificazione dei circuiti elettrici, lo sviluppo di nuovi algoritmi di controllo e uno studio sulla generalizzazione del posizionamento dei magneti. Questa tesi in particolare è incentrata su questa ultima parte: è stato studiato in simulazione il campo magnetico che i magneti genererebbero se fossero disposti in una conformazione ellittica anzichè circolare, come nel sistema fisico. Questa ricerca è stata ritenuta interessante in quanto potrebbe portare allo sviluppo di strategie di controllo più sofisticate (e interessanti per l'utilizzatore del sistema) per la levitazione dell'oggetto levitante. Queste modifiche richiedono l'analisi di diversi fattori: primo, come variano le equazioni differenziali che descrivono il sistema; secondo, come dovrebbe cambiare la posizione dei sensori per mantenere ottimale la misurazione del campo magnetico; terzo, scoprire quali sono i nuovi limiti dell'abilità di controllare l'oggetto levitante dettati dalle componenti fische del sistema, come attuatori e sensori, considerando che questi dovrebbero avere un costo limitato per rispettare gli obbiettivi del progetto.This thesis is part of a larger project in collaboration with the Norwegian University of Science and Technology, NTNU, and it has the objective of designing and building a maglev platform that is cheap, relatively easy to assemble, and reprogrammable. The intuition is that this platform may be used by students taking control systems subjects, that could then build their own system to experiment with, and develop a better understanding of the theoretical concepts behind control. The first steps of this project were taken by a series of NTNU students in their bachelor thesis, “Magnetic levitation systems: design, prototyping and testing of a digital PID-controller”. This first work built a platform that used permanent magnets and actively controlled solenoids (using PID control) to magnetically levitate a magnet. It also developed a mathematical framework in Matlab to simulate the system. This thesis reports part of a new round of development of the system, performed in collaboration with two other students from University of Padova, Alberto Morselli and Andrea Nicetto. This round overhauls the electrical circuits of the system, improves the control algorithms, and generalizes the results to other mechanical designs. This thesis focuses in particular on this generalization: we attempt to modify the system design to simulate the magnetic field the magnets would generate if they were placed in an elliptical arrangement instead of the original circular arrangement. This change in the disposition of the magnets is indeed deemed as allowing to implement more sophisticated (and interesting for the users) control strategies for the levitating magnet. This adaptation requires the accomplishment of several tasks: first, altering the ODEs to suit the new design; second, changing the positions of the sensors for the magnetic field as they may not be optimal anymore; third, finding which new limitations in the ability to control the levitating magnet are given by physical components such as actuators and sensors, since they must have a limited cost for the system to be affordable