Independent Control of Multiple Degrees of Freedom Local Magnetic Actuators with Magnetic Cross-coupling Compensation

This letter tackles the problem of independent control of multiple degrees of freedom (DoF) systems based on local magnetic actuation (LMA). This is achieved by means of a modular disturbance rejection scheme, with the aim of enhancing the range of use of multiple-DoF LMAs in dexterous surgical manipulators. An LMA actuation unit consists of a pair of permanent magnets, characterized by diametrical magnetization, acting as magnetic gears across the abdominal wall. In this study, the model of the LMA and the time-varying magnetic disturbances owing to the proximity of multiple units are discussed. Subsequently, the developed model is capitalized in order to establish a Kalman state observer for the purpose of developing a sensor-free endoscopic manipulator suited to infer the state of the internal side of the LMA. Afterwards, the same model is used to develop an adaptive feedforward compensator system, with the aim of balancing the magnetic torques acting on the LMAs from the neighboring units in the case of unknown and frequency-varying sinusoidal disturbances. The effect of a magnetic shield, realized by means of MuMetal is also analyzed. The overall control system is modular with respect to the number of units and requires no centralized intelligence. The proposed scheme is subsequently validated by means of experiments performed on a benchtop platform, showing the effectiveness of the proposed approach. In particular, the proposed state observer presents a root mean square error (RMSE) ranging from 28 to 47 rpmin the estimation of the rotational velocity of the internal magnet and an RMSE of 1.18 to 1.41 mNm in the estimation of a load torque. The disturbance compensation system provides a reduction of 40% to 50% in the disturbance caused by interacting LMA units

Space science/space station attached payload pointing accommodation study: Technology assessment white paper

Technology assessment is performed for pointing systems that accommodate payloads of large mass and large dimensions. Related technology areas are also examined. These related areas include active thermal lines or power cables across gimbals, new materials for increased passive damping, tethered pointing, and inertially reacting pointing systems. Conclusions, issues and concerns, and recommendations regarding the status and development of large pointing systems for space applications are made based on the performed assessments

Magnetic Actuators and Suspension for Space Vibration Control

The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals

Advanced flight control system study

The architecture, requirements, and system elements of an ultrareliable, advanced flight control system are described. The basic criteria are functional reliability of 10 to the minus 10 power/hour of flight and only 6 month scheduled maintenance. A distributed system architecture is described, including a multiplexed communication system, reliable bus controller, the use of skewed sensor arrays, and actuator interfaces. Test bed and flight evaluation program are proposed

Extended analytical charge modeling for permanent-magnet based devices : practical application to the interactions in a vibration isolation system

This thesis researches the analytical surface charge modeling technique which provides a fast, mesh-free and accurate description of complex unbound electromagnetic problems. To date, it has scarcely been used to design passive and active permanent-magnet devices, since ready-to-use equations were still limited to a few domain areas. Although publications available in the literature have demonstrated the surface-charge modeling potential, they have only scratched the surface of its application domain. The research that is presented in this thesis proposes ready-to-use novel analytical equations for force, stiffness and torque. The analytical force equations for cuboidal permanent magnets are now applicable to any magnetization vector combination and any relative position. Symbolically derived stiffness equations directly provide the analytical 3 £ 3 stiffness matrix solution. Furthermore, analytical torque equations are introduced that allow for an arbitrary reference point, hence a direct torque calculation on any assembly of cuboidal permanent magnets. Some topics, such as the analytical calculation of the force and torque for rotated magnets and extensions to the field description of unconventionally shaped magnets, are outside the scope of this thesis are recommended for further research. A worldwide first permanent-magnet-based, high-force and low-stiffness vibration isolation system has been researched and developed using this advanced modeling technique. This one-of-a-kind 6-DoF vibration isolation system consumes a minimal amount of energy (Ç 1W) and exploits its electromagnetic nature by maximizing the isolation bandwidth (> 700Hz). The resulting system has its resonance > 1Hz with a -2dB per decade acceleration slope. It behaves near-linear throughout its entire 6-DoF working range, which allows for uncomplicated control structures. Its position accuracy is around 4mum, which is in close proximity to the sensor’s theoretical noise level of 1mum. The extensively researched passive (no energy consumption) permanent-magnet based gravity compensator forms the magnetic heart of this vibration isolation system. It combines a 7.1kN vertical force with <10kN/m stiffness in all six degrees of freedom. These contradictory requirements are extremely challenging and require the extensive research into gravity compensator topologies that is presented in this thesis. The resulting cross-shaped topology with vertical airgaps has been filed as a European patent. Experiments have illustrated the influence of the ambient temperature on the magnetic behavior, 1.7h/K or 12N/K, respectively. The gravity compensator has two integrated voice coil actuators that are designed to exhibit a high force and low power consumption (a steepness of 625N2/W and a force constant of 31N/A) within the given current and voltage constraints. Three of these vibration isolators, each with a passive 6-DoF gravity compensator and integrated 2-DoF actuation, are able to stabilize the six degrees of freedom. The experimental results demonstrate the feasibility of passive magnet-based gravity compensation for an advanced, high-force vibration isolation system. Its modular topology enables an easy force and stiffness scaling. Overall, the research presented in this thesis shows the high potential of this new class of electromagnetic devices for vibration isolation purposes or other applications that are demanding in terms of force, stiffness and energy consumption. As for any new class of devices, there are still some topics that require further study before this design can be implemented in the next generation of vibration isolation systems. Examples of these topics are the tunability of the gravity compensator’s force and a reduction of magnetic flux leakage

International Symposium on Magnetic Suspension Technology, Part 1

The goal of the symposium was to examine the state of technology of all areas of magnetic suspension and to review related recent developments in sensors and controls approaches, superconducting magnet technology, and design/implementation practices. The symposium included 17 technical sessions in which 55 papers were presented. The technical session covered the areas of bearings, sensors and controls, microgravity and vibration isolation, superconductivity, manufacturing applications, wind tunnel magnetic suspension systems, magnetically levitated trains (MAGLEV), space applications, and large gap magnetic suspension systems

A lifting and actuating unit for a planar nanoprecision drive system

Ein wesentlicher Treiber in vielen heutigen Technologiebereichen ist die Miniaturisierung von elektrischen, optischen und mechanischen Systemen. Mehrachsige Geräte mit großen Verfahrbereichen und extremer Präzision spielen dabei nicht nur in der Messung und Qualitätssicherung, sondern auch in der Fabrikation und Manipulation von Nanometerstrukturen eine entscheidende Rolle. Die vertikale Bewegungsaufgabe stellt eine besondere Herausforderung dar, da die Schwerkraft des bewegten Objektes permanent kompensiert werden muss. Diese Arbeit schlägt dafür eine Vertikalhub- und -aktuiereinheit vor und trägt damit zur Weiterentwicklung von Nanometer-Präzisionsantriebssystemen bei. Grundlegende mögliche kinematische Integrationsvarianten werden betrachtet und entsprechend anwendungsrelevanter Kriterien gegenübergestellt. Der gezeigte parallelkinematische Ansatz zeichnet sich durch seine gute Integrierbarkeit, geringe negative Einflüsse auf die umliegenden Systeme, sowie die Verteilung der Last auf mehrere Stellglieder aus. Folgend wird ein konstruktiver Entwicklungsprozess zusammengestellt, um diese favorisierte Variante weiter auszuarbeiten. Im Laufe dieses Prozesses wird die zu entwickelnde Einheit in das Gesamtsystem eingeordnet und ihre Anforderungen, Randbedingungen und enthaltenen Teilsysteme definiert. Die vertikale Aktuierung besteht dabei aus zwei Systemen: Einer pneumatische Gewichtskraftkompensation und einem elektromagnetischen Präzisionsantrieb. Das technische Prinzip der Hubeinheit wird erstellt und die Teilsysteme im verfügbaren Bauraum angeordnet. Daraus wird ein detailliertes Modell des pneumatischen Aktors abgeleitet, dieser dimensioniert und dessen Eigenschaften bestimmt. Die Ausdehnung dieses Teilsystems definiert die räumlichen Grenzen für den umliegenden Präzisionsantrieb. Zur Auslegung dieses Antriebs wird das Kraft-/Leistungsverhältnis als Zielgröße definiert. Mit Hilfe von numerischer Simulation und Optimierung werden Geometrien für verschiedenste Topologien entworfen und bewertet. Die geeignetste Variante wird mit allen Teilsystemen in eine Einheit integriert und auskonstruiert. Abschließend werden zukünftige Schritte für die Integration der Einheit in ein Präzisionsantriebssystem dargestellt und mögliche Anwendungsszenarien in der Nanofabrikation präsentiert.A central driver in many of today's fields of technology is the miniaturization of electrical, optical and mechanical systems. Multi-axis devices with large travel ranges and extreme precision play a decisive role, not only in measurement and quality assurance, but also in the fabrication and manipulation of nanometer structures. The vertical movement task poses a special challenge, since the gravitational load of the moving object must be compensated permanently. This thesis proposes a vertically lifting and actuating unit and thus contributes to the further development of nanometer precision drive systems. Basic possible kinematic integration variants are considered and compared according to application relevant criteria. The presented parallel kinematic approach is characterized by its good integrability, its minimal negative influences on the surrounding systems, as well as the distribution of the load to several actuators. Subsequently, a constructive development process is compiled to further develop this favoured variant. During this process the unit to be developed is integrated into the overall system. Further, its requirements, boundary conditions and subsystems are defined. The vertical actuation consists of two systems: A pneumatic weight force compensation and an electromagnetic precision drive. The technical principle of the lifting unit is developed and the subsystems are arranged in the available design space. Based on this, a detailed model of the pneumatic actuator is created, its dimensions derived and properties obtained. These dimensions define the spatial limits for the surrounding precision actuator. For the design of this actuator, the force-power ratio is chosen as the objective quantity. Using numerical simulations and optimization, geometries for various topologies are created and evaluated. The most suitable variant is designed and integrated with all other subsystems into one unit. Finally, upcoming steps for integrating the unit into a precision drive system are outlined and possible future applications in the field of nanofabrication are presented

Neuromechanical Tuning for Arm Motor Control

Movement is a fundamental behavior that allows us to interact with the external world. Its importance to human health is most evident when it becomes impaired due to disease or injury. Physical and occupational rehabilitation remains the most common treatment for these types of disorders. Although therapeutic interventions may improve motor function, residual deficits are common for many pathologies, such as stroke. The development of novel therapeutics is dependent upon a better understanding of the underlying mechanisms that govern movement. Movement of the human body adheres to the principles of classic Newtonian mechanics. However, due to the inherent complexity of the body and the highly variable repertoire of environmental contexts in which it operates, the musculoskeletal system presents a challenging control problem and the onus is on the central nervous system to reliably solve this problem. The neural motor system is comprised of numerous efferent and afferent pathways with a hierarchical organization which create a complex arrangement of feedforward and feedback circuits. However, the strategy that the neural motor system employs to reliably control these complex mechanics is still unknown. This dissertation will investigate the neural control of mechanics employing a “bottom-up” approach. It is organized into three research chapters with an additional introductory chapter and a chapter addressing final conclusions. Chapter 1 provides a brief description of the anatomical and physiological principles of the human motor system and the challenges and strategies that may be employed to control it. Chapter 2 describes a computational study where we developed a musculoskeletal model of the upper limb to investigate the complex mechanical interactions due to muscle geometry. Muscle lengths and moment arms contribute to force and torque generation, but the inherent redundancy of these actuators create a high-dimensional control problem. By characterizing these relationships, we found mechanical coupling of muscle lengths which the nervous system could exploit. Chapter 3 describes a study of muscle spindle contribution to muscle coactivation using a computational model of primary afferent activity. We investigated whether these afferents could contribute to motoneuron recruitment during voluntary reaching tasks in humans and found that afferent activity was orthogonal to that of muscle activity. Chapter 4 describes a study of the role of the descending corticospinal tract in the compensation of limb dynamics during arm reaching movements. We found evidence that corticospinal excitability is modulated in proportion to muscle activity and that the coefficients of proportionality vary in the course of these movements. Finally, further questions and future directions for this work are discussed in the Chapter 5

Nonlinear Control of a Flexible Rotor Magnetic Bearing System: Robustness and the Indefinate Model

Previously published control strategies for magnetic bearings primarily focus on linear optimal control techniques. While these methods afford many advantages, conspicuously absent from the literature are detailed attempts at nonlinear control. Here, we obtain the equations of motion of an overhung flexible rotor supported in magnetic bearings with two different levels of model sophistication. We derive a generic nonlinear controller in the manner of feedback linearization, and compare the eigenanalysis and transient response of the two rotor models under the action of this >perfect model> controller. We then proceed to obtain a robust nonlinear controller through the sliding mode technique and demonstrate that robustness by implementing it on an uncertain model.Center for Electromechanic

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