Smart double panel with decentralised active damping units for the control of sound transmission

This thesis presents a comprehensive study of a smart aircraft double panel for active vibroacoustic control. The control of the double panel vibration is implemented using Multi-Input-Multi-Output (MIMO) decentralised velocity feedback loops. The loops are applied via an array of electrodynamic force actuators and collocated velocity sensors. The actuators are located in an air cavity between the two panels such that they can react against the two panels. Two velocity sensors per actuator are used. Either sensor is located at the source and radiating panel footprint of an actuator. The error velocity is formed by subtracting weighted sensor outputs. In the introductory part of the thesis a survey of aircraft interior noise is given, and stateof- the-art passive and active noise control methods are presented. In Chapter two the mathematical model for the theoretical analysis of the smart double panel is formulated and a parametric study of passive sound transmission is performed using the mathematical model. In Chapter three the performance of decentralised feedback control systems using absolute and relative velocity is analysed theoretically. In Chapter four the stability and performance of decentralised feedback control systems using reactive actuators driven with weighted velocity error signals is analysed theoretically. In Chapter five the stability of decentralised feedback control systems using weighted velocity error signals and electrodynamic reactive actuators is analysed experimentally. In Chapter six the performance of decentralised feedback control systems using weighted velocity error signals and reactive actuators is analysed experimentally.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Model-based nonlinear control of active tilting-pad bearings

A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The proposed active tilting-pad bearing has linear actuators that radially translate each pad. The use of feedback control in determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the operation of the rotating machine. In the first part of the dissertation, we develop a nonlinear dynamic model of the active bearing system. The hydrodynamic force produced by the fluid film is modeled as a nonlinear, squeeze-film damper plus repellent spring. A model-based nonlinear controller is then designed to exponentially regulate the rotor position to the origin. A proof-of-concept experiment shows that the active strategy improves the bearing performance relative to its traditional passive operation. Further, the experiment demonstrates that the model-based nonlinear control regulates the rotor comparably to a linear PID control, but requires significantly less control energy. The second part of the dissertation introduces a new type of active fluid-film bearing which actively adjusts the angular velocity of the pads of a tilting-pad bearing. This is motivated by the observation that there is more control authority in the pad tilting motion than in its radial translation. To this end, a dynamic model for the bearing system is developed, inclusive of the nonlinear hydrodynamic force for the infinitely-short bearing case. A model-based controller is then constructed, based on measurements of the journal position and velocity and pad tilting angles, to ensure that the journal is asymptotically regulated to the bearing center. Numerical simulations illustrate the performance of the active bearing under the proposed control in comparison with the bearing\u27s standard passive mode of operation

Vibration isolation with smart fluid dampers: a benchmarking study

The non-linear behaviour of electrorheological (ER) and magnetorheological (MR) dampers makes it difficult to design effective control strategies, and as a consequence a wide range of control systems have been proposed in the literature. These previous studies have not always compared the performance to equivalent passive systems, alternative control designs, or idealised active systems. As a result it is often impossible to compare the performance of different smart damper control strategies. This article provides some insight into the relative performance of two MR damper control strategies: on/off control and feedback linearisation. The performance of both strategies is benchmarked against ideal passive, semi-active and fully active damping. The study relies upon a previously developed model of an MR damper, which in this work is validated experimentally under closed-loop conditions with a broadband mechanical excitation. Two vibration isolation case studies are investigated: a single-degree-of-freedom mass-isolator, and a two-degree-of-freedom system that represents a vehicle suspension system. In both cases, a variety of broadband mechanical excitations are used and the results analysed in the frequency domain. It is shown that although on/off control is more straightforward to implement, its performance is worse than the feedback linearisation strategy, and can be extremely sensitive to the excitation conditions

Hardware-in-the-loop simulation of magnetorheological dampers for vehicle suspension systems

Magnetorheological (MR) fluids provide an elegant means to enhance vibration control in primary vehicle suspensions. Such fluids can rapidly modify their flow characteristics in response to a magnetic field, so they can be used to create semi-active dampers. However, the behaviour of MR dampers is inherently non-linear and as a consequence, the choice of an effective control strategy remains an unresolved problem. Previous research has developed a method to linearize the damper's force/velocity response, to allow implementation of classical control techniques. In the present study, this strategy is used to implement skyhook damping laws within primary automotive suspensions. To simulate the vehicle suspension, a two-degree-of-freedom quarter car model is used, which is excited by realistic road profiles. The controller performance is investigated experimentally using the hardware-in-the-loop-simulation (HILS) method. This experimental method is described in detail and its performance is validated against numerical simulations for a simplified problem. The present authors demonstrate that feedback linearization can provide significant performance enhancements in terms of passenger comfort, road holding, and suspension working space compared with other control strategies. Furthermore, feedback linearization is shown to desensitize the controller to uncertainties in the input excitation such as changes in severity of the road surface roughness

Feedback control unit with an inerter proof-mass electrodynamic actuator

In this study the use of an inerter is considered for active vibration control of a structure excited by white noise. The structure is modelled as a single degree of freedom system and the control system consists of a vibration absorber with a mass suspended on a spring, a damper and an inerter. The absorber is equipped with a reactive force transducer in parallel with the passive suspension which is driven with a signal proportional to the velocity of the structure under control measured by an ideal collocated sensor. The effect of the inerter on the control stability and performance of the control system is investigated. It is shown that the effect of the inerter is to reduce the natural frequency of the inertial actuator, improving the stability of the feedback loop and thus its performance. The optimisation of the physical and control parameters of the control system such as the internal damping of the actuator, its natural frequency, its inertance and the feedback gain are considered such that either the kinetic energy of the host structure is minimised or the power dissipated by the control system is maximised

Robot Impedance Control and Passivity Analysis with Inner Torque and Velocity Feedback Loops

Impedance control is a well-established technique to control interaction forces in robotics. However, real implementations of impedance control with an inner loop may suffer from several limitations. Although common practice in designing nested control systems is to maximize the bandwidth of the inner loop to improve tracking performance, it may not be the most suitable approach when a certain range of impedance parameters has to be rendered. In particular, it turns out that the viable range of stable stiffness and damping values can be strongly affected by the bandwidth of the inner control loops (e.g. a torque loop) as well as by the filtering and sampling frequency. This paper provides an extensive analysis on how these aspects influence the stability region of impedance parameters as well as the passivity of the system. This will be supported by both simulations and experimental data. Moreover, a methodology for designing joint impedance controllers based on an inner torque loop and a positive velocity feedback loop will be presented. The goal of the velocity feedback is to increase (given the constraints to preserve stability) the bandwidth of the torque loop without the need of a complex controller.Comment: 14 pages in Control Theory and Technology (2016

A Passivity-based Nonlinear Admittance Control with Application to Powered Upper-limb Control under Unknown Environmental Interactions

This paper presents an admittance controller based on the passivity theory for a powered upper-limb exoskeleton robot which is governed by the nonlinear equation of motion. Passivity allows us to include a human operator and environmental interaction in the control loop. The robot interacts with the human operator via F/T sensor and interacts with the environment mainly via end-effectors. Although the environmental interaction cannot be detected by any sensors (hence unknown), passivity allows us to have natural interaction. An analysis shows that the behavior of the actual system mimics that of a nominal model as the control gain goes to infinity, which implies that the proposed approach is an admittance controller. However, because the control gain cannot grow infinitely in practice, the performance limitation according to the achievable control gain is also analyzed. The result of this analysis indicates that the performance in the sense of infinite norm increases linearly with the control gain. In the experiments, the proposed properties were verified using 1 degree-of-freedom testbench, and an actual powered upper-limb exoskeleton was used to lift and maneuver the unknown payload.Comment: Accepted in IEEE/ASME Transactions on Mechatronics (T-MECH

Vibration control strategies for proof-mass actuators

Proof-mass actuators have been considered for a broad range of structural vibration control problems, from seismic protection for tall buildings to the improvement of metal machining productivity by stabilizing the self-excited vibrations known as chatter. This broad range of potential applications means that a variety of controllers have been proposed, without drawing direct comparisons with other controller designs that have been considered for different applications. This article takes three controllers that are potentially suitable for the machining chatter problem: Direct velocity feedback, tuned-mass-damper control (or vibration absorber control), and active-tuned-mass-damper control (or active vibration absorber control). These control strategies are restated within the more general framework of Virtual Passive Control. Their performance is first compared using root locus techniques, with a model based on experimental data, including the low frequency dynamics of the proof-mass. The frequency response of the test structure is then illustrated under open and closed-loop conditions. The application of the control strategies to avoid machine-tool chatter vibrations is then discussed, without going into detail on the underlying physical mechanisms of chatter. It is concluded that virtual passive absorber control is more straightforward to implement than virtual skyhook damping, and may be better suited to the problem of machining chatter