Aircraft are often confronted with distinct circumstances during different parts of their mission. Ideally the
aircraft should fly optimally in terms of aerodynamic performance and other criteria in each one of these mission
requirements. This requires in principle as many different aircraft configurations as there are flight conditions, so
therefore a morphing aircraft would be the ideal solution. A morphing aircraft is a flying vehicle that i) changes
its state substantially, ii) provides superior system capability and iii) uses a design that integrates innovative
technologies. It is important for such aircraft that the gains due to the adaptability to the flight condition are not
nullified by the energy consumption to carry out the morphing manoeuvre. Therefore an aeroelastic numerical
tool that takes into account the morphing energy is needed to analyse the net gain of the morphing. The code
couples three-dimensional beam finite elements model in a co-rotational framework to a lifting-line aerodynamic
code. The morphing energy is calculated by summing actuation moments, applied at the beam nodes, multiplied
by the required angular rotations of the beam elements. The code is validated with NASTRAN Aeroelasticity
Module and found to be in agreement. Finally the applicability of the code is tested for a sweep morphing
manoeuvre and it has been demonstrated that sweep morphing can improve the aerodynamic performance of an
aircraft and that the inclusion of aeroelastic effects is important.
KEYWORDS: Control systems design, Firearms, Actuators, Lead, Control systems, Electronics, Motion measurement, Power supplies, Smart materials, Computer engineering
While good marksmanship is the key to the effectiveness of the infantry mission, all soldiers experience a decrease in
accuracy due to combat stress that generates detrimental physiological effects. INSTAR is a tactical rifle designed to
address these effects by decoupling unwanted shooter-induced disturbances from the barrel via an active suspension
system. Previous papers have addressed the design of the active suspension system: the actuation, driving electronics
and power supply. In this paper we consider the development of the jitter control system. Beginning with an analytical
model of the gun that includes the shooter, we develop the appropriate model for the design of the control system. We
investigate two designs. The first design is based on lead compensation. The second design is based on LQG. Both
designs show that the control system can effectively reduce the jitter to acceptable levels. The classical compensator
demonstrates better transient performance.
Electrostrictor transducers are attractive because of their (relatively) large displacements. However, they exhibit a quadratic nonlinearity between the charge and displacement as well as a nonlinear relationship between charge and voltage. These nonlinearities limit the useful range for linear output. For example, in acoustic applications, these nonlinearities limit the range of displacements that do not generate higher order harmonics. In this paper we describe a nonlinear electronic controller to mitigate the effects of the material nonlinearity. We also provide a stability proof for the nonlinear controller. This proof is based on a Lyapunov stability proof for a nonlinear capacitor with modifications.
The constitutive behavior of magnetostrictive materials exhibits many nonlinearities. One of the dominate nonlinearities is the quadratic dependence between the drive current and the transducer displacement. While the transducer can be operated at low drive levels with little distortion, at high drive levels the square law distortion is evident. In this paper we propose a nonlinear feedback loop for the drive amplifier such that the amplifier provides a compensation for this transducer nonlinearity. Thus the combination of the amplifier and the magnetostrictive transducer presents a linear input output relationship to the user. The effectiveness of this nonlinear control is demonstrated in simulation.
Smart structures typically consist of many interacting components, which result in a closed loop formed by an actuator, structure, sensors, controller, and drive circuit components. Despite the recognition of component interactions, much of the traditional design approach for such systems is highly compartmentalized and sequential. The primary objective of the present work is to develop a basic understanding of the energy flow and dynamic interaction between the electrical and mechanical subsystems of smart actuators. When operating from portable power sources, a crucial factor in determining the performance of such a smart system is the battery capacity required for the actuator to operate through a given time span along with its life time. The real and reactive power in such a system will determine the battery life and size separately. While the real power is dissipated only in the drive circuit, the reactive power of the circuit and the actuator cannot be calculated individually, where the interaction arises. Multi-objective function optimization problem, which combines the real and reactive power by different weights, will result in a better balanced solution than optimizing either one of them separately. Genetic algorithm is applied for discrete component selection to generate more realistic designs. The optimization result is illustrated in the paper, as well as their relationship with multi-objective functions.
While good marksmanship is key to the effectiveness of the infantry mission, all soldiers experience a decrease in accuracy due to combat stress that generates detrimental physiological effects. INSTAR is a tactical rifle designed to address these effects by decoupling unwanted shooter-induced disturbances from the barrel via an active suspension system. The critical design driver for this active suspension was the "complete" actuation system (actuation, driving electronics and power supply). This paper presents an overview to the INSTAR architectural design along with the challenging actuation requirements. The architectural development and experimental performance characterization of the selected Recurve piezoceramic actuation system is discussed in detail along with the specialized driving electronics needed for power conservation. Range-of-motion experiments were conducted on a full-scale, 1 DOF INSTAR prototype, demonstrating the necessary actuation system control authority for a successful active suspension.
A high-efficiency driving amplifier with small profile for smart actuators is essential for portable actuator devices. In this paper, a detailed optimized design of half-bridge switching circuit to drive smart actuators is described. The mathematical optimization procedure is applied to the traditional circuit design to make the circuit smaller and more efficient. The objecitve function presented in this paper is to minimize the total weight of the circuit, including heat sink, inductor and bus capacitor. The calculation of the power dissipation of MOSFET is adopted as a critical step to get the suitable heat sink. The optimization results are presented to demonstrate the effectiveness of this method.
The power requirements imposed on an active vibration control system are quite important to the overall system design. In order to improve the efficiency we analyze different feedback control strategies which will provide electrical energy regeneration. The active isolation system is modeled in a state-space form for two different types of actuators: a piezoelectric stack actuator and a linear electromagnetic (EM) actuator. During regenerative operation, the power is flowing from the mechanical disturbance through the electromechanical actuator and its switching drive into the electrical storage device (batteries or capacitors). We demonstrate that regeneration occurs when controlling one or both of the flow states (velocity and/or current). This regenerative control strategy affects the closed loop dynamics of the isolator which sees its damping reduced.
Good marksmanship is critical to infantry mission effectiveness. In combat there are intense external simulations such as incoming fire, loud noises. There is fear of the unknown and death, especially with the witnessing of loss of life. Unfortunately, the stress generated by all these pressures produces detrimental physiological effects. Studies have shown that the heart beat of a soldier in combat is aroudn 300 beats per minute. In addition to this, the soldiers breathing and muscle jerk increases, significantly reducing accuracy. This lost accuracy severely reduces the change of soldier survival, mission effectiveness and increase colateral damage and civilian casualiteis. These stressors are well known to the military.
Electrical power distribution for recently developed smart actuators becomes an important air-vehicle challenge if projected smart actuation benefits are to be met. Among the items under development are variable shape inlets and control surfaces that utilize shape memory alloys (SMA); full span, chord-wise and span-wise contouring trailing control surfaces that use SMA or piezoelectric materials for actuation; and other strain-based actuators for buffet load alleviation, flutter suppression and flow control. At first glance, such technologies afford overall vehicle performance improvement, however, integration system impacts have yet to be determined or quantified. Power systems to support smart structures initiatives are the focus of the current paper. The paper has been organized into five main topics for further discussion: (1) air-vehicle power system architectures - standard and advanced distribution concepts for actuators, (2) smart wing actuator power requirements and results - highlighting wind tunnel power measurements from shape memory alloy and piezoelectric ultrasonic motor actuated control surfaces and different dynamic pressure and angle of attack; (3) vehicle electromagnetic effects (EME) issues, (4) power supply design considerations for smart actuators - featuring the aircraft power and actuator interface, and (5) summary and conclusions.
We consider the integrated optimization of electrically driven Recurve actuators. The drive circuit is based on a half-bridge switching amplifier topology. Both actuator and circuit physical design variables are considered in the optimization formulation. The objective is to minimize the weight of the system while satisfying performance and stability constraints. The interactions and trade offs between the actuator and the drive circuit are investigated. Optimization results show clear interrelations between the design of the electric circuit and the actuator. The optimization is based on an integrated model of the electronics with the Recurve actuator. A finite element model for Euler-Bernoulli beams is developed with appropriate coupling interface to the drive circuit. The proposed finite element model correctly considers charge variation over the actuator and leads to an energy conservative formulation. The structural model is coupled to the electric circuit model via charge-voltage transfer function.
The Inertially Stabilized Rifle is a new stabilized rifle system that can eliminate the disturbances induced by the shooter. Recurve actuator is used in this system to provide the precise movement of the rifle barrel. In such a portable device, only low voltage electrical sources are available yet the piezoelectric actuator needs high voltage to drive the actuator. The actuators consume little real power but a large amount of reactive power. Furthermore, the piezoelectric actuators are present an almost purely capacitive load. In this paper, we describe the development of a low input voltage amplifier for a high voltage piezoelectric actuator. This amplifier is based on switching technology so it efficiently handles the regenerative energy from the piezoelectric actuator. This amplifier consists of two stages. The first stage is a flyback converter which boosts the (low) input voltage to the maximum voltage required by the piezoelectric actuator. The second stage is a half-bridge amplifier which delivers the output voltage to the actuator as commanded by the reference signal. The basic structure of the amplifier is described, and its performance is characterized in terms of bandwidth, distortion, and efficiency.
The power requirements imposed on a active vibration isolation system are quite important to the overall system design. In order to improve the efficiency of an active isolation system we analyze different feedback control strategies which will provide an electrical energy regeneration. In this case, the power is flowing from the mechanical disturbance through the electromechanical actuator and its switching drive into the electrical storage device (batteries or capacitors). We demonstrate that regeneration occurs when controlling one or both of the flow states (velocity and current). This regenerative control strategy also affects the closed loop dynamics. The regenerative control applied to a voice-coil actuator results in a closed loop system which has a reduced amount of damping compared to the initial system. In fact the regenerative control strategy will increase the level of vibration compared to the closed electrical circuit boundary condition in order to make the system absorb more energy, of which a part is transferred to an electrical storage device.
KEYWORDS: Amplifiers, Actuators, Control systems, Feedback control, Device simulation, Systems modeling, Signal attenuation, Computing systems, Ferroelectric materials, Vibration control
The power requirements imposed on the amplifier by piezoelectric actuators in both open and closed loop vibration suppression control systems is discussed. We consider a two-degree-of-freedom mechanical system driven by a piezoelectric stack for the purpose of analyzing power flow and power dissipation. A state space model for this system that includes the electrical input and output variables of the piezoelectric actuator is developed. The power requirements of the open loop system are measured and compared to simulations performed with the state-space model. Results show that the simulations correlate well with the measured data. We then investigate the power requirements for two closed-loop vibration suppression control schemes. We show that the closed-loop power flow and power dissipation is a function of the type of feedback control law implemented. In our simulations, a feedback controller that introduces significant damping (approximately 70% critical) increases the frequency range in which real power is flowing between the actuator and the mechanical system. A controller that introduces only light damping is primarily reactive over the frequency range studied but exhibits a narrowband region of real power flow. Linear amplifier analysis demonstrates that the closed-loop control system must be considered in determining the power dissipation requirements for the control system.
The formulation of an optimization problem for the design of a current controlled switching power amplifier to drive a piezoelectric actuator is the subject of this paper. The design is formulated as a continuous optimization problem. A detailed model that includes the anhysteretic nonlinearity between the electric field and polarization is developed and is coupled with a dynamic model of the amplifier. The design specifications are formulated as optimization constraints. The objective function is chosen to be the weight of the inductor. Optimization results are presented to demonstrate the efficiency of the proposed design morphology.
The effect of bidirectional power flow on the power distribution system of an aircraft is addressed in this paper. The active vibration control problem of the tail surface of an aircraft using piezoelectric actuators is chosen to motivate the study presented. A simple dynamic model of the tail surface is developed. A current controlled switched-mode power amplifier is used to drive the actuators. The integration of the `amplifier-actuator' into the power distribution system of the aircraft is studied in detail. The effect of circulating energy between the actuators and the DC bus on the voltage on the bus is explained. Solutions to avoid instability and undesirable distortion in the DC bus voltage are proposed.
KEYWORDS: Actuators, Control systems, Earthquakes, Control systems design, Electronics, Feedback control, Power supplies, Wind energy, Structural design, Magnetism
This study explores the use of a linear PMDC machine as a regenerative force actuator for the mitigation of earthquake disturbances in civil structures. Unlike previous studies of this kind, the control system developed is purely active, meaning no 'hybrid' control techniques are used, such as the combination of active force actuation and passive tuned mass dampers. Modeling methods for the machine as well as its associate drive electronics are briefly described. It is shown that for this purely active system, it is possible and feasible to develop regenerative excitation schemes which drive the machine primarily by absorbing power from the excited building. Such regenerative excitation makes it possible to isolate the actuator from the external power grid, which is necessary during earthquakes, where the quality, or even the mere availability of external power is questionable. Furthermore, results are presented which find the minimum reservoir of energy necessary to excite the machine during the beginning of the earthquake, and it is shown that the actuator local power supply will see a gain in energy across the duration of the disturbance. The control system design methods presented employ position feedback. Then, force limiting techniques are employed to regulate power flow in the machine. The effectiveness of this control design is evaluated on a 3-story building, and performance is briefly compared to that of semi-active control designs proposed elsewhere.
In this paper, the power flow between stacked electrostrictor actuators and a pulse-width-modulated switching amplifier is analyzed. The amplifier and actuator are components of a smart skin whose function is underwater acoustic echo cancellation. An integrated model is developed with includes a dynamic structural model of the actuator, a dynamic model of the power electronics and a nonlinear electromechanical coupling mechanism of the electrostrictor actuation materials.Using a linearized model, the mechanical admittance of the actuator seen by an external force is analyzed. An outer acoustic control loop is shown to modify this mechanical admittance and optimize the power coupling between the actuator and an external fluid medium by impedance matching. Effective power flow occurs only when the frequency of the external force is within the bandwidth of the amplifier.
In this paper we develop an integrated model of the amplifier, actuator material, and structural dynamics of a smart material. Stacked electrostrictor actuators are driven by a PWM amplifier. These actuators are attached to a graphite epoxy composite base and they drive an alumina headmass. The whole device, designed from underwater acoustics, is potted. We model the actuators using nonlinear constitutive laws. These equations are integrated into a dynamic model of the amplifier. Then these equations are integrated with a dynamic model of the actuator. Finally, a finite element model is developed for the multilayered composite material that provides the dynamic response of the device. Using superelements, stiffness coefficients are extracted from the finite element model of the multilayered composite material.
In this paper we report on the development of a high frequency switching amplifier for electrostrictive actuators. This amplifier is specifically designed for the capacitive loads that electrostrictive actuator present to them. An integrated nonlinear model of the actuator and the electronics is also developed. It is shown that one source of distortion in the actuator velocity is the nonlinear field to polarization relationship. The amplifier reduces the impact of this nonlinearity by controlling the current entering the actuator instead of the voltage across the actuator. Another major source of the distortion is caused by the quadratic relationship between polarization and strain in the electrostrictive material. The paper develops a new control scheme for the amplifier which significantly improves the linearity of the overall amplifier/actuator combination. Both experimental and simulation results of the Smart Material are reported.
In this paper we are concerned with Smart Materials that contain many actuators and sensors along with digital signal processing electronics that allow for the implementation of a control algorithm. Smart Materials have been proposed for the active control of sound from a vibrating structure. Here we investigate the design of structural control systems for these Smart Structures for noise suppression. First we model the radiated acoustic waves in terms of the velocity of the surface of the structure. Then we formulate an optimal control problem as a linear system that has a transmission zero in the path between the disturbance force and the shape that radiates best. A geometric description of the problem relates control problem to the acoustics. This optimal control problem is solved using a genetic algorithm.
In this paper we report on the development of a high frequency switching amplifier for electrostrictive actuators. This amplifier is specifically designed for the capacitive loads that electrostrictive actuator present to them. One of the ultimate goals is to miniaturize these amplifiers so that they could be embedded into the material along with the actuators. Therefore, the configuration was chosen that would allow for miniaturization. The amplifier is also designed for high efficiency for thermal management. An integrated nonlinear model of the actuator and the electronics is also developed. A prototype Smart Material was fabricated consisting of sixty four actuators and sixteen amplifiers. Both experimental and simulation results of the Smart Material are reported.
In this paper we are concerned with Smart Materials that contain many actuators and sensors along with digital signal processing electronics that allow for the implementation of a control algorithm. Smart Materials have been proposed for the active control of sound from a vibrating structure. Here we investigate the design of structural control systems for these Smart Structures for noise suppression. First we model the radiated acoustic waves in terms of the velocity of the surface of the structure. Then we formulate an optimal control problem as a linear system that has a transmission zero in the path between the disturbance force and the shape that radiates best.
A procedure is developed for mapping strain sensor readings into displacements. Optimal sensor layouts are determined by examining predicted mode shapes from synthesized strain data. The singular values of the transformation matrix bound the error in the inferred displacements. Issues of spatial aliasing as well as sensor spacing are also addressed. The methodology was validated by comparing both static and dynamic shape estimations with experiments.
KEYWORDS: Actuators, Sensors, Control systems, Control systems design, Finite element methods, Bridges, Wheatstone bridges, Resistance, Feedback control, Systems modeling
While the phenomenon of shifts in the poles of flexible structures caused by local stiffening due to bonded piezoceramic actuators is well documentated, shifts in the zeros associated with the distorted mode shapes due to localized stiffening has yet to be investigated. The finite element method in conjunction with state space models was used to derive transfer functions for both collocated and noncollocated sensor/actuator pairs. Models that considered the mode shape distortions compared favorably with experimental measurements. With the numerical models validated by experiments, state variable feedback control gains were determined using linear quadratic regulator design for noncollocated and collocated sensor/actuator pairs for the cases of classical mode shapes and distorted mode shapes. It is demonstrated that lack of consideration of distorted mode shapes can lead to a loss of performance of the control systems.
The next generation of materials will contain many embedded or attached actuators and/or sensors. They will also contain support electronics including power electronics and a computer processor with a communication network along with the `smarts' to respond to their environment. Current research is also directed toward miniaturization of the components, particularly the sensor and actuators with the idea of incorporating large numbers of actuators and sensors into the material. In keeping with this trend, the electronics should also be miniaturized along with the sensors and actuators. In this paper we discuss miniaturized power converters and power systems with potential applications to materials with miniaturized sensors and actuators.
In this paper we describe a new algorithm for the detection, location, and estimation of damage on a space truss using parameter identification techniques. The concept is to start with a model of the truss which is known to accurately model the healthy truss. This healthy model of the truss is periodically updated using dynamic response data. When damage has occurred, a damage model of the truss is constructed from dynamic response data using an identification algorithm. By comparing the parameters in the truth model with the parameters of the damage model, the damage is detected, located, and the extent of the damage accessed. The algorithm proposed here uses an explicit model of the damage to the truss. This description of the damage allows the algorithm search over a smaller set of possible damage models with attendant increase in performance. In addition to locating the damage, an estimate of the damage is also given. The performance of this algorithm for locating and estimating damage is presented in the form of three example problems including a 44 dof planar truss.
One definition of a smart structure is a structure with a miniaturized control system embedded in or attached to the material for improved performance of the structure. The feasibility of embedding piezoelectric sensors and actuators has been demonstrated. Current research is focusing on the development of the support electronics for these sensors and actuators. In this paper we discuss miniaturized power conversion/amplifier electronics for these actuators suitable for these smart structure applications. State-of-the-art dc to dc power converters with a 2 square inch footprint and a 1/4 in profile with power densities up to 50 W/in3 with efficiencies above 80% are described. The power converters to minimize thermal dissipation. The power bus requirements are also discussed.
Recently there has emerged a new class of sensors, called spatial filters, for structures which respond over a significant gauge length. Examples include piezoelectric laminate PVDF film, modal domain optical fiber sensors, and holographic sensors. These sensors have a unique capability in that they can be fabricated to locally alter their sensitivity to the measurand. In this paper we discuss how these sensors can be used for the implementation of control algorithms for the suppression of acoustic radiation from flexible structures. Based on this relationship between the total power radiated to the far field to the modal velocities of the structure, we show how the sensor placement to optimize the control algorithm to suppress the radiated power.
Modal domain optical fiber sensors have recently been employed in the implementation of system identification algorithms and the closed-loop control of vibrations in flexible structures. The mathematical model of the modal domain optical fiber sensor used in these applications, however, only accounted for the effects of strain in the direction of the fiber's longitudinal axis. In this paper, we extend this model to include the effects of arbitrary stress. Using this sensor model, we characterize the sensor's sensitivity and dynamic range.
Modal domain optical fiber sensors, or distributed effect sensors, for active vibration suppression in flexible structures are considered. Preliminary modeling results indicate that these sensors can be used to sense vibrations in a flexible beam and the signal can be used to damp vibrations in the beam. Weighted distributed-effect sensors can be used to implement high order compensators with low order functional observers.
In this paper we discuss the use of a distributed-effect modal domain optical fiber
sensor (MD sensor) as a component in an active control system to suppression vibrations in
a flexible beam. We integrate the sensor model into the model for a flexible structure.
Based on this system model, a control system with a dynamic compensator is designed to
add damping to the low order modes of the flexible structure. To verify the modeling
procedure a cantilevered beam was instrumental with a piezoelectric actuator and an MD
sensor. It is shown that experimental responses closely match simulated responses for both open ioop and closed loop tests.
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