Title page for ETD etd-042808-124333

Document Type dissertation

Author Name Potami, Raffaele

URN etd-042808-124333

Title Optimal sensor/actuator placement and switching schemes for control of flexible structures

Degree PhD

Department Mechanical Engineering

Advisors
Demetriou, Michael A., Advisor
Richman, Mark W., Committee Member
Hussein, Islam, Committee Member
Grigoriadis, Karolos M. , Committee Member
Gatsonis, Nikolaos A., Graduate Committee Rep

Keywords
hybrid system
PZT actuators
performance enhancement
actuator placement
actuator switching

Date of Presentation/Defense 2008-04-24

Availability unrestricted

Abstract
The vibration control problem for flexible structures is examined
within the context of overall controller performance and power
reduction. First, the issue of optimal sensor and actuator
placement is considered along with its associated control
robustness aspects. Then the option of alternately activating
subsets of the available devices is investigated. Such option is
considered in order to better address the effects of
spatiotemporally varying disturbances acting on a flexible
structure while reducing the overall energy consumption.

Towards the solution to the problem of optimal device placement,
three different approaches are proposed. First, a computationally
efficient scheme for the simultaneous placement of multiple
devices is presented. The second approach proposes a strategy for
the optimal placement of sensors and collocated sensor/actuator
pairs, taking into account the influence of the spatial
distribution of disturbances. The third approach provides a
solution to the actuator location problem by incorporating
considerations with respect to preferred spatial regions within
the flexible structure.

Then the second problem named above is considered. Activating a
subset of the available and optimally placed actuators and sensors
in a flexible structure provides enhanced performance with reduced
energy consumption. Such approach of switching on and off
different actuating devices, depending on their local-in-time
authority, results in a hybrid system. Therefore the proposed work
draws on existing results on hybrid systems and includes an
additional degree of freedom, whereby both the actuating devices
and the control signals allocated to them are switched in and out.
To enable this switching an activation strategy, which insures
also that stability-under-switching is guaranteed, is required.
Three different strategies are considered for such actuators
allocation: first a cost-to-go index is considered, then a cost
function based on the mechanical energy of the flexible structure
and finally a performance index based on the maximum deviation of
the transverse displacement.

A flexible aluminum plate was chosen to validate and test the
proposed approaches. The set up utilized four pairs of collocated
piezoceramic patches that serve to provide sensing and actuating
capabilities. Extensive numerical simulations were performed for
both the placement strategies and the switching policies proposed,
in order to predict the behavior of the flexible plate and provide
the optimal actuator and sensor locations that were to be affixed
on the flexible structure.

Finally, to complete the validation process a sequence of
experimental tests were performed. The objective of these tests
was to compare the performance of the proposed hybrid control
system to traditional non switched control schemes. In order to
provide a repeatable perturbation, four of the piezoceramic
patches were allocated to simulate a spatiotemporally varying
disturbance, while the remaining four patches were used as sensors
and controlling actuators. The experimental results showed a
significant performance improvement for the switched controller
over the traditional controller. Moreover the switched controller
exhibited improved robustness towards spatiotemporally varying
disturbances while the traditional controller showed a significant
loss of controller performance. The improvement achieved in
vibration control problems could be extended to a wider range of
applications. In particular, although this study was concentrated
on a rectangular thin plate, the proposed strategies can be
applied to emph{any} structure and more generally to any plant
whose dynamics can be represented by a second order linear system.
For example, by removing the restriction of spatially fixed
actuators and sensors, the proposed theory can be applied to the
problem of unmanned vehicles control.

Files
Raffaele_Potami.pdf

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Document Type	dissertation
Author Name	Potami, Raffaele
URN	etd-042808-124333
Title	Optimal sensor/actuator placement and switching schemes for control of flexible structures
Degree	PhD
Department	Mechanical Engineering
Advisors	Demetriou, Michael A., Advisor Richman, Mark W., Committee Member Hussein, Islam, Committee Member Grigoriadis, Karolos M. , Committee Member Gatsonis, Nikolaos A., Graduate Committee Rep
Keywords	hybrid system PZT actuators performance enhancement actuator placement actuator switching
Date of Presentation/Defense	2008-04-24
Availability	unrestricted
Abstract The vibration control problem for flexible structures is examined within the context of overall controller performance and power reduction. First, the issue of optimal sensor and actuator placement is considered along with its associated control robustness aspects. Then the option of alternately activating subsets of the available devices is investigated. Such option is considered in order to better address the effects of spatiotemporally varying disturbances acting on a flexible structure while reducing the overall energy consumption. Towards the solution to the problem of optimal device placement, three different approaches are proposed. First, a computationally efficient scheme for the simultaneous placement of multiple devices is presented. The second approach proposes a strategy for the optimal placement of sensors and collocated sensor/actuator pairs, taking into account the influence of the spatial distribution of disturbances. The third approach provides a solution to the actuator location problem by incorporating considerations with respect to preferred spatial regions within the flexible structure. Then the second problem named above is considered. Activating a subset of the available and optimally placed actuators and sensors in a flexible structure provides enhanced performance with reduced energy consumption. Such approach of switching on and off different actuating devices, depending on their local-in-time authority, results in a hybrid system. Therefore the proposed work draws on existing results on hybrid systems and includes an additional degree of freedom, whereby both the actuating devices and the control signals allocated to them are switched in and out. To enable this switching an activation strategy, which insures also that stability-under-switching is guaranteed, is required. Three different strategies are considered for such actuators allocation: first a cost-to-go index is considered, then a cost function based on the mechanical energy of the flexible structure and finally a performance index based on the maximum deviation of the transverse displacement. A flexible aluminum plate was chosen to validate and test the proposed approaches. The set up utilized four pairs of collocated piezoceramic patches that serve to provide sensing and actuating capabilities. Extensive numerical simulations were performed for both the placement strategies and the switching policies proposed, in order to predict the behavior of the flexible plate and provide the optimal actuator and sensor locations that were to be affixed on the flexible structure. Finally, to complete the validation process a sequence of experimental tests were performed. The objective of these tests was to compare the performance of the proposed hybrid control system to traditional non switched control schemes. In order to provide a repeatable perturbation, four of the piezoceramic patches were allocated to simulate a spatiotemporally varying disturbance, while the remaining four patches were used as sensors and controlling actuators. The experimental results showed a significant performance improvement for the switched controller over the traditional controller. Moreover the switched controller exhibited improved robustness towards spatiotemporally varying disturbances while the traditional controller showed a significant loss of controller performance. The improvement achieved in vibration control problems could be extended to a wider range of applications. In particular, although this study was concentrated on a rectangular thin plate, the proposed strategies can be applied to emph{any} structure and more generally to any plant whose dynamics can be represented by a second order linear system. For example, by removing the restriction of spatially fixed actuators and sensors, the proposed theory can be applied to the problem of unmanned vehicles control.
Files	Raffaele_Potami.pdf