Vibration suppression and slewing control of a flexible structure

Examined here are the effects of motor dynamics and secondary piezoceramic actuators on vibration suppression during the slewing of flexible structures. The approach focuses on the interaction between the structure, the actuators, and the choice of control law. The results presented here are all simulated, but are based on experimentally determined parameters for the motor, structure, piezoceramic actuators, and piezofilm sensors. The simulation results clearly illustrate that the choice of motor inertia relative to beam inertia makes a critical difference in the performance of the system. In addition, the use of secondary piezoelectric actuators reduces the load requirements on the motor and also reduces the overshoot of the tip deflection. The structures considered here are a beam and a frame. The majority of results are based on a Euler Bernoulli beam model. The slewing frame introduces substantial torsional modes and a more realistic model. The slewing frame results are incomplete and represent work in progress

Vibration Suppression of a Spacecraft Flexible Appendages Using Smart Material

The article of record as published may be found at http://dx.doi.org/10..1088/0964-1726/7/1/011This paper presents the results of positive position feedback (PPF) control and linear–quadratic Gaussian (LQG) control for vibration suppression of a flexible structure using piezoceramics. Experiments were conducted on the US Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is comprised of a rigid central body and a flexible appendage. The objective of this research is to suppress the vibration of the flexible appendage. Experiments show that both control methods have unique advantages for vibration suppression. PPF control is effective in providing high damping for a particular mode and is easy to implement. LQG control provides damping to all modes; however, it cannot provide high damping for a specific mode. LQG control is very effective in meeting specific requirements, such as minimization of tip motion of a flexible beam, but at a higher implementation cost.This paper presents the results of positive position feedback (PPF) control and linear–quadratic Gaussian (LQG) control for vibration suppression of a flexible structure using piezoceramics. Experiments were conducted on the US Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is comprised of a rigid central body and a flexible appendage. The objective of this research is to suppress the vibration of the flexible appendage. Experiments show that both control methods have unique advantages for vibration suppression. PPF control is effective in providing high damping for a particular mode and is easy to implement. LQG control provides damping to all modes; however, it cannot provide high damping for a specific mode. LQG control is very effective in meeting specific requirements, such as minimization of tip motion of a flexible beam, but at a higher implementation cost.This paper presents the results of positive position feedback (PPF) control and linear–quadratic Gaussian (LQG) control for vibration suppression of a flexible structure using piezoceramics. Experiments were conducted on the US Naval Postgraduate School’s flexible spacecraft simulator (FSS), which is comprised of a rigid central body and a flexible appendage. The objective of this research is to suppress the vibration of the flexible appendage. Experiments show that both control methods have unique advantages for vibration suppression. PPF control is effective in providing high damping for a particular mode and is easy to implement. LQG control provides damping to all modes; however, it cannot provide high damping for a specific mode. LQG control is very effective in meeting specific requirements, such as minimization of tip motion of a flexible beam, but at a higher implementation cost

TIP trajectory tracking of flexible-joint manipulators

In most robot applications, the control of the manipulator’s end-effector along a specified desired trajectory is the main concern. In these applications, the end-effector (tip) of the manipulator is required to follow a given trajectory. Several methods have been so far proposed for the motion control of robot manipulators. However, most of these control methods ignore either joint friction or joint elasticity which can be caused by the transmission systems (e.g. belts and gearboxes). This study aims at development of a comprehensive control strategy for the tip-trajectory tracking of flexible-joint robot manipulators. While the proposed control strategy takes into account the effect of the friction and the elasticity in the joints, it also provides a highly accurate motion for the manipulator’s end-effector. During this study several approaches have been developed, implemented and verified experimentally/numerically for the tip trajectory tracking of robot manipulators. To compensate for the elasticity of the joints two methods have been proposed; they are a composite controller whose design is based on the singular perturbation theory and integral manifold concept, and a swarm controller which is a novel biologically-inspired controller and its concept is inspired by the movement of real biological systems such as flocks of birds and schools of fishes. To compensate for the friction in the joints two new approaches have been also introduced. They are a composite compensation strategy which consists of the non-linear dynamic LuGre model and a Proportional-Derivative (PD) compensator, and a novel friction compensation method whose design is based on the Work-Energy principle. Each of these proposed controllers has some advantages and drawbacks, and hence, depending on the application of the robot manipulator, they can be employed. For instance, the Work-Energy method has a simpler form than the LuGre-PD compensator and can be easily implemented in industrial applications, yet it provides less accuracy in friction compensation. In addition to design and develop new controllers for flexible-joint manipulators, another contribution of this work lays in the experimental verification of the proposed control strategies. For this purpose, experimental setups of a two-rigid-link flexible-joint and a single-rigid-link flexible-joint manipulators have been employed. The proposed controllers have been experimentally tested for different trajectories, velocities and several flexibilities of the joints. This ensures that the controllers are able to perform effectively at different trajectories and speeds. Besides developing control strategies for the flexible-joint manipulators, dynamic modeling and vibration suppression of flexible-link manipulators are other parts of this study. To derive dynamic equations for the flexible-link flexible-joint manipulators, the Lagrange method is used. The simulation results from Lagrange method are then confirmed by the finite element analysis (FEA) for different trajectories. To suppress the vibration of flexible manipulators during the manoeuvre, a collocated sensor-actuator is utilized, and a proportional control method is employed to adjust the voltage applied to the piezoelectric actuator. Based on the controllability of the states and using FEA, the optimum location of the piezoelectric along the manipulator is found. The effect of the controller’s gain and the delay between the input and output of the controller are also analyzed through a stability analysis

Modeling and shape estimation of smart structures for active control

Piezoelectric materials allow the transformation of electric constraints into mechanical constraints and vice versa. They are used as controllers or sensors in the industrial field. The analysis of the behavior of piezoelectric materials lays within the use of these materials in structures whose form or modes of vibration are to be controlled. The need for these studies is crucial. From a general point of view, the need for stability of structures has become increasingly important with the development of technologies related to telecommunications and microtechniques. Adaptive structures are the only means to achieve the requisite stability in the face of diverse situations. The objective of this research is to model the effect of electro- mechanical coupling and to estimate the shape of the adaptive structures for active control. Ideal models were developed for various adaptive structures. These models make it possible to determine the static and dynamic behavior of these structures. The model behavior was compared with experimental results and the, numerical, finite elements and the Rayleigh-Ritz methods. Results obtained from all of the above approaches reveal good agreements among them. For a possible application of active control, the analysis of substructures in commercial FEA software ANSYS is used to extract the mass, the rigidity and input matrices. In order to evaluate at real time the shape of the flexible or composite structures, an algorithm was developed to determine the forms of the structures under arbitrary loads and different boundary conditions. The results obtained by this method were compared with those obtained from numerical, the finite elements and experimental methods. The results also, show that the developed algorithm makes it possible to correctly estimate the structures

Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, part 2

A collection of papers presented at the Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems is given. The papers address modeling, systems identification, and control of flexible aircraft, spacecraft and robotic systems

Modeling and sliding-mode control of flexible-link robotic structures for vibration suppression

In many applications, the use of slender and light flexible structures has increased due to the requirement of more energetically efficient structures. This kind of structures is easily prone to vibrate due to external forces or due to forces generated in the inner structure during the movement. One objective of this work is to generate models of flexible-link structures: cantilever beam, one flexible-link robot and two flexible-link robot; which include rotational actuators, piezoelectric actuators, and different kinds of sensors (acceleration and deformation). The models are obtained under a classical mechanics approach of Lagrange Euler energy balance; the assumed mode method is used to approximate the flexibility of the elastic components. In the model formulation, new rotation angles are introduced in the distal joints and the joint inertia is separated according to this new kinematic consideration. Some parts of the resulting model involving integral terms are calculated using symbolic programming software; whereas other parts are implemented and calculated dynamically during simulation. The resulting models are programmed in Matlab/Simulink subjected to a novel verification methodology and then validated experimentally in a platform constructed for the implementation. The second objective is to develop, from simplified models of the flexible-link structures, robust controllers for joint tracking and active vibration suppression. Therefore, robust control is used with two basic purposes: to face the model uncertainties due to the discrepancies between the models and real systems and to suppress the vibration of the flexible-link structures. Three control strategies are proposed: Dual loop control approach, decentralized and centralized Lyapunov model-based sliding mode control approach. The values required for the implementation of the controller are obtained from the formulated models. The controllers were implemented in a dSPACE rapid prototyping control card and the experimental results show the effectiveness of the proposed control strategies in terms of joint tracking and vibration suppression.In viele Anwendungen, die Nutzung von schlanken und leichten Strukturen ist wegen Energieanforderungen gestiegen. Solche Strukturen sind anfällig für Schwingung wegen äußere Kräfte oder innere erzeugen Kräfte während der Bewegung. Ein Ziel dieser Arbeit handelt sich um die Erzeugung von verschiedener flexiblen-Glied Strukturen z.B. Kragarm, ein und zwei flexibel-Glied Roboter. Die Strukturen enthalten: rotatotische Aktoren, piezoelektrische Aktoren und verschiedene Sensoren (Beschleunigung und Dehnung). Die Modelle werden im Rahmen klassisches Ansatz von Lagrange Euler Energiebilanz entwickelt; die Angenommene Mode Methode (Assumed Mode Method) wird verwendet, um die Flexibilität der elastischen Komponenten zu approximieren. In der Modellformulierung werden neue Rotationswinkel in die distalen Gelenke eingeführt und die gemeinsame Trägheit gemäß dieser neuen kinematischen Betrachtung getrennt. Einige Elemente des resultierenden Modells integrale Begriffe beinhalten, werden mit symbolischen Programmiersoftware berechnet; während andere Teile umgesetzt und dynamisch aus der Simulation berechnet. Die resultierenden Modelle werden in Matlab/Simulink programmiert, sie werden unter eine neuartige Methodologie verifiziert unterworfen und dann validiert in experimentell in einem Prüfstand. Das zweite Ziel ist von vereinfachten Modellen robuste Controller für die Gelenkablaufverfolgung und aktive Schwingungsunterdrückung zu entwickeln. Daher ist eine robuste Regelung mit zwei grundlegende Zwecke verwendet: die Modellunsicherheiten zu berücksichtigen aufgrund der Unterschiede zwischen den Modellen und realen Systemen und die Schwingung der flexiblen Strukturen zu unterdrücken. Drei Kontrollstrategien werden vorgeschlagen: Dual Regel Ansatz, dezentrale und zentrale Lyapunov modellbasierten Sliding Mode Control Ansätze. Die erforderlichen Werte für die Ausführung der Steuerung sind aus den formulierten Modellen erhalten. Die Regler wurden in einer dSPACE Rapid-Prototyping-Steuerkarte implementiert. Die experimentellen Ergebnisse zeigen die Wirksamkeit der vorgeschlagenen Kontrollstrategien in Bezug auf die Gelenkablaufverfolgung und Schwingungsunterdrückung

The Fifth NASA/DOD Controls-Structures Interaction Technology Conference, part 1

This publication is a compilation of the papers presented at the Fifth NASA/DoD Controls-Structures Interaction (CSI) Technology Conference held in Lake Tahoe, Nevada, March 3-5, 1992. The conference, which was jointly sponsored by the NASA Office of Aeronautics and Space Technology and the Department of Defense, was organized by the NASA Langley Research Center. The purpose of this conference was to report to industry, academia, and government agencies on the current status of controls-structures interaction technology. The agenda covered ground testing, integrated design, analysis, flight experiments and concepts

MIT Space Engineering Research Center

The Space Engineering Research Center (SERC) at MIT, started in Jul. 1988, has completed two years of research. The Center is approaching the operational phase of its first testbed, is midway through the construction of a second testbed, and is in the design phase of a third. We presently have seven participating faculty, four participating staff members, ten graduate students, and numerous undergraduates. This report reviews the testbed programs, individual graduate research, other SERC activities not funded by the Center, interaction with non-MIT organizations, and SERC milestones. Published papers made possible by SERC funding are included at the end of the report

Technology for large space systems: A bibliography with indexes (supplement 16)

This bibliography lists 673 reports, articles and other documents introduced into the NASA scientific and technical information system between July 1, 1986 and December 31, 1986. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

MIT's interferometer CST testbed

The MIT Space Engineering Research Center (SERC) has developed a controlled structures technology (CST) testbed based on one design for a space-based optical interferometer. The role of the testbed is to provide a versatile platform for experimental investigation and discovery of CST approaches. In particular, it will serve as the focus for experimental verification of CSI methodologies and control strategies at SERC. The testbed program has an emphasis on experimental CST--incorporating a broad suite of actuators and sensors, active struts, system identification, passive damping, active mirror mounts, and precision component characterization. The SERC testbed represents a one-tenth scaled version of an optical interferometer concept based on an inherently rigid tetrahedral configuration with collecting apertures on one face. The testbed consists of six 3.5 meter long truss legs joined at four vertices and is suspended with attachment points at three vertices. Each aluminum leg has a 0.2 m by 0.2 m by 0.25 m triangular cross-section. The structure has a first flexible mode at 31 Hz and has over 50 global modes below 200 Hz. The stiff tetrahedral design differs from similar testbeds (such as the JPL Phase B) in that the structural topology is closed. The tetrahedral design minimizes structural deflections at the vertices (site of optical components for maximum baseline) resulting in reduced stroke requirements for isolation and pointing of optics. Typical total light path length stability goals are on the order of lambda/20, with a wavelength of light, lambda, of roughly 500 nanometers. It is expected that active structural control will be necessary to achieve this goal in the presence of disturbances