The active vibration control of a submerged cylindrical shell by piezoelectric sensors and actuators is investigated. The
fluid is assumed to be inviscid and irrotational in developing a theoretical model. The cylindrical shell is modelled by
using the Rayleigh- Ritz method based on the Donnell-Mushtari shell theory. The fluid motion is modelled based on the
baffled shell model, which is applied to the fluid-structure interaction problem. The kinetic energy of the fluid is derived
by solving the boundary-value problem. The resulting equations of motion are expressed in matrix form, which enables
us to design control easily. The natural vibration characteristics of the cylindrical shell in air and in water are
investigated both theoretically and experimentally. The experimental results show that the natural frequencies of the
submerged cylindrical shell decrease to a great extent compared the natural frequencies in air. However, the natural
mode shapes for lower modes are not different from the mode shapes in air. Two MFC actuators were glued to the shell
and the positive position feedback control was applied. Experiments on the active vibration control of the submerged
cylindrical shell were carried out in water tank. Both theoretical and experimental results showed that both vibrations and
sound radiation can be suppressed by piezoelectric actuators.
This paper is concerned with the modeling of the rectangular plate bonded with rectangular piezoceramic sensors and actuators, which can have an arbitrary angle with respect to the plate axis. The equations of motion were derived by the Rayleigh-Ritz method. The cantilever plate with piezoceramic sensors and actuators was built to verify the theoretical development. The theoretical frequency response curve based on the equations of motion was then compared to the experimental frequency response curve. The sensor and actuator characteristics were also studied both theoretically and experimentally. The sensor characteristic is defined as the ratio of the tip displacement to the voltage output and the actuator characteristic is defined as the ratio of the applied voltage to the tip displacement. The final objective of the research is to optimize the sensor and actuator locations as well as orientation to maximize the control performance. The control performance will follow.
This paper is concerned with the development of an active vibration isolation device using PZT wafers. The main task of the device is to protect vibration-sensitive instruments from hazardous environments. The device developed in this study consists of S-shaped supporters bonded with PZT wafers, passive damping materials and piezoceramic sensors that can measure the relative motion between the base and the platform. The newly developed device can produce discernible displacement thus providing a way of counteracting external disturbances. Control techniques, which can fully utilize the functions of the device, are also developed. The experimental results show that the proposed device and the control techniques are capable of isolating vibrations thus useful in protecting sensitive instruments from external vibrations.
This research is concerned with the adaptive positive position feedback (PPF) controller design for the vibration suppression of smart structures. The main advantage of the PPF controller is that it can tackle the target mode without disturbing other modes. However, its major drawback is that we should tune the PPF filter frequency to the natural frequency of the target mode. In this study, we developed a new algorithm, which can adaptively trace the optimal PPF filter frequency in real time. To this end, we applied the gradient descent method to the digital PPF controller and derived the adaptive PPF control algorithm in digital form, which can be implemented in real time. The proposed adaptive PPF controller was tested using the simple beam structure. The experimental results show that the adaptive PPF controller is capable of tuning the PPF filter frequency to the optimal one in real time thus achieving vibration suppression in changing environments.
This paper is concerned with the development of the passive-active vibration absorber using piezoelectric actuators. The active vibration absorber system consists of 2 pairs of PZT actuators bonded on aluminum plates making s- shaped device. Hence, the active system is directly connected to the passive system. The rubber attached to the end of the beam is connected to the upper base as a structural member. It allows bending thus maximizing the vertical movement generated by the piezoceramic actuators. This paper also presents the development and the verification of the control techniques for the passive-active vibration absorber. The vibration absorber can be utilized as a passive vibration absorber when the controller is off. It is shown that vibrations can be reduced by 20dB for the first mode, when the SISO PPF controller is operated. The advantage of PPF controller provides us the most effective way of increasing damping for the particular mode of interest. However, the natural mode should be computed in the process of design, to maximize the performance. In reality the target natural frequency is estimated by the frequency response of the vibration-absorbing device and is later applied to the PPF controller as a filter frequency. In this paper, the adaptive PPF controller is considered to cope with the structural change, so that it can modify the filler frequency based on the measurement. It is found that the adaptive PPF controller is effective for the active vibration absorber when the external disturbance is applied with various excitation frequencies. It can be concluded that the proposed passive-active vibration absorber is an effective way of reducing the vibration amplitude of the precise devices in the harsh environments thus enhancing the precision.
KEYWORDS: Sensors, Semiconducting wafers, Actuators, Smart structures, Ferroelectric materials, Motion models, Digital signal processing, Active vibration control, Space robots, Vibration control
This research is concerned with the modeling and active vibration control of slewing smart structures. When cantilever beam rotates about axes perpendicular to the undeformed beam's longitudinal axis, it experiences inertial loading. Hence, the beam vibrates during and after slewing. In this paper, the analytical model for a single slewing flexible beam with surface bonded piezoelectric sensor and actuator is first developed using the Hamilton's principle with discretization by the assumed mode method. The theoretical frequency response function is then compared to the experimental open loop frequency response data. It is found from the comparison that the rotor friction should be included in the modeling. A new concept is introduced to incorporate the effect of the friction. As a result, the use of coupling factor is proposed in this paper. The positive position feedback, (PPF) controller is designed for the suppression of residual vibrations after slewing. The experimental results show that it can suppress the vibration effectively but cannot alleviate the vibrations occurred during slewing. This problem is discussed in detail in this paper.
KEYWORDS: Genetic algorithms, Digital signal processing, Sensors, Smart structures, Actuators, Feedback control, Composites, Amplifiers, Finite element methods, Active vibration control
This paper is concerned with the real-time automatic tuning of the multi-input multi-output positive position feedback controllers for smart structures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searching optimal design parameters without falling into local minimums thus rendering globally optimal solutions. The previous real-time algorithm that tunes a single control parameter is extended to tune more parameters of the MIMO PPF controller. We employ the MIMO PPF controller since it can enhance the damping value of a target mode without affecting other modes if tuned properly. Hence, the traditional positive position feedback controller can be used in adaptive fashion in real time. The final form of the MIMO PPF controller results in the centralized control, thus it involves many parameters. The bounds of the control parameters are estimated from the theoretical model to guarantee the stability. As in the previous research, the digital MIMO PPF control law is downloaded to the DSP chip and a main program, which runs genetic algorithms in real time, updates the parameters of the controller in real time. The experimental frequency response results show that the MIMO PPF controller tuned by GA gives better performance than the theoretically designed PPF. The time response also shows that the GA tuned MIMO PPF controller can suppress vibrations very well.
This paper is concerned with design, manufacturing and performance test of lightweight THUNDER using a top fiber composite layer with near-zero CTE, a PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by the lightweight fiber reinforced plastic layers without losing capabilities to generate high force and displacement. It is possible to save weight up to about 30 percent if we replace the metallic backing materials by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature by following autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detaching form a flat mold. From experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDER.
This paper is concerned with the viscoelastic strain-energy hinge for solar array deployment. The original strain-energy hinge proposed by TRW for solar array deployment was made of strip measures. Due to its structural simplicity, the strain-energy hinge has been considered as an alternative to the torsional spring type deployment mechanism. However, theoretical modeling of the strain-energy hinge is extremely difficult because of its nonlinear pre- and post-buckling dynamic behavior. To investigate its dynamic characteristics, series of buckling and deployment tests on a single strain-energy hinge and a solar array structure equipped with strain-energy hinge have been conducted. The deployment test results show that there remain residual vibrations after deployment, which are resulted from the rapid deployment and the bending flexibility of the strain- energy hinge. We propose the use of viscoelastic material embedded between the layers of the strip measure to increase the passive damping. It results in less residual vibrations and smooth deployment. Experimental results show that viscoelastic strain-energy hinge ins superior to the ordinary strain-energy hinge in deployments. Based on the experiments on the single strain-energy hinge, an equivalent 1D torsional spring model is proposed. Simulation results based on the equivalent model are fairly in good agreement with experimental results.
KEYWORDS: Genetic algorithms, Amplifiers, Sensors, Actuators, Control systems, Active vibration control, Analog electronics, Smart structures, Feedback control, System identification
This paper is concerned with the optimal tuning of digitally programmable analog controllers on the ACTEX-1 smart structures flight experiment. The programmable controllers for each channel include a third order Strain Rate Feedback (SRF) controller, a fifth order SRF controller, a second order Positive Position Feedback (PPF) controller, and a fourth order PPF controller. Optimal manual tuning of several control parameters can be a difficult task even though the closed-loop control characteristics of each controller are well known. Hence, the automatic tuning of individual control parameters using Genetic Algorithms is proposed in this paper. The optimal control parameters of each control law are obtained by imposing a constraint on the closed-loop frequency response functions using the ACTEX mathematical model. The tuned control parameters are then uploaded to the ACTEX electronic control electronics and experiments on the active vibration control are carried out in space. The experimental results on ACTEX will be presented.
KEYWORDS: Genetic algorithms, Digital signal processing, Smart structures, Sensors, Actuators, Feedback control, Amplifiers, Algorithm development, Active vibration control, Control systems
This paper is concerned with the real-time automatic tuning of the positive position feedback controller for smart structures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searching optimal design parameters without falling into local minimums thus rendering globally optimal solutions. The advantage of the positive position feedback controller is that if it is tuned properly it can enhance the damping value of a target mode without affecting other modes. In this paper, we develop a real-time algorithm for determining a tuning frequency of the PPF controller based on the genetic algorithm. Hence, the traditional positive position feedback controller can be used in adaptive fashion in real time. To this end, the digital PPF control law is downloaded to the DSP chip and a main program, which runs genetic algorithms in real time, updates the parameter of the controller in real time. The real-time tuning of the PPF controller is applied to cases of initial disturbance and persistent harmonic disturbance. In both cases, the real-time tuning is achieved successfully. Hence, vibrations are suppressed satisfactorily. The experimental results also show that the PPF controller tuned by GA gives better performance than the manually tuned PPF controller for accommodating harmonic disturbances did.
This paper is concerned with the determination of multiple positive position feedback controller gains using genetic algorithms. The genetic algorithms have proven its effectiveness in searching optical design parameters without falling into local minima thus rendering globally optimal solutions. The use of genetic algorithms to the controller design have been investigated by many researchers but limited to the PID control, and optimal controls. In this paper, the genetic algorithm is applied to the positive position feedback control which has been successfully used for the active vibration suppression of smart structures. The advantage of the positive position feedback controller is that it can be easily implemented in analog circuits and each mode can be tackled independently. However, the disadvantage is that the natural vibration characteristics should be accurately determined a priori either theoretically or experimentally. In this paper, we develop a new algorithm for the determination of controller gains based on the genetic algorithm. Hence, the traditional positive position feedback controller can be used in adaptive fashion. Experimental results will prove its effectiveness.
KEYWORDS: Control systems, Sensors, Actuators, Intelligence systems, Smart structures, Modeling, Amplifiers, Data modeling, Analog electronics, Systems modeling
This paper presents preliminary modelling and vibration suppression experiment results for the USAF Phillips Laboratory's Planar Articulating Controls Experiment (PACE) test bed. PACE is a two link flexible multibody experiment constrained to move over the surface of a large granite table. In this paper, an approximate analytical dynamic model of a single slewing flexible body with surface bonded piezoelectric sensors and actuators is developed using Hamilton's Principle with discretization by the assumed modes method. After conversion to modal coordinates, damping is added to the model by including experimental damping measurements. The model is then converted to state-space form for the purpose of control design. The model is verified by comparison of simulated and experimental open loop frequency response data. Both decentralized and centralized controllers are designed for vibration suppression of a single arm of the PACE test bed. The controllers presented in this paper include: a positive position feedback (PPF) controller for controlling the first mode of vibration, a decentralized controller which uses three independent PPF filters for suppressing the first three modes of vibration, and a multiple-input, multiple-output linear quadratic gaussian design. The experiments include both analog and digital implementations of these controllers.
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