A systematic distributed optimal control design procedure is proposed for the rejection of wind load-induced disturbances on a truss-supported segmented mirror. The distributed nature of the controller is achieved by weighing of the interaction matrices between local (per-segment) controllers in a global H 2 optimization. The procedure allows a tradeoff analysis between the controller implementation complexity versus the improved performance the extra communication brings. The procedure is demonstrated on a finite element model of a segmented mirror on a flexible supporting truss to which we apply the combined closed-loop performance and local controller interconnection structure optimization. The resulting set of controllers is compared to a set of baseline controllers including linear-quadratic-Gaussian control, singular value decomposition control, and a distributed controller where local controllers of neighboring segments communicate. The tradeoff analysis for the segmented mirror demonstrates that the communication between the local controllers can be greatly reduced without significantly compromising the rejection of wind-induced wavefront errors.

This paper discusses a concept of bimorph deformable mirror used in adaptive optics to compensate for manufacturing errors, gravity release and thermal distortion affecting large lightweight mirrors in space telescopes. The mirror consists of a single-crystal Silicon wafer (D=75 mm t=500μm) covered with an optical coating on the front side and an array of 25 independent PZT actuators acting in d31 mode on the back side. The mirror is mounted on an isostatic support with three linear PZT actuators controlling the rigid-body motion. The paper presents the experimental results obtained with this design and a new, more compact alternative.

This paper considers the piezoelectric resistive and inductive RL shunt damping applied to rotationally periodic structures equipped with an array of regularly spaced piezoelectric patches. A method for simplifying the hardware, by reducing the size of the inductors and eliminating the use of synthetic inductors, is described. The paper compares two different ways of using the piezoelectric array: independent loops and parallel loops. It shows that, if a specific mode with n nodal diameters is targeted, mounting 4n piezoelectric patches in two parallel loops is as efficient as mounting them in 4n independent loops, while considerably reducing the demand on the inductors, L, (by 4n(2)). The method takes advantage of the mode shapes of rotationally periodic structures. The proposed method is validated numerically and experimentally on a rotationally periodic circular plate (nearly axisymmetric). The proposed technique is aimed at turbomachinery applications.

This paper explores the feasibility of active damping of suspension bridges with the addition of stay cables controlled by active tendons. An active tendon consists of a displacement actuator collocated with a force sensor monitoring the tension in the cable. The active tendons are controlled by decentralized integral force feedback (IFF). In the first part of the paper, the potential of the control strategy is evaluated on a numerical model of an existing footbridge; several configurations are investigated where the active cables connect the pylon to the deck or the deck to the catenary. The analysis confirms that it is possible to provide a set of targeted modes with a considerable amount of damping, reaching xi = 15%. In the second part of the paper, the control strategy is demonstrated experimentally on a laboratory mock-up equipped with four control stay cables equipped with piezoelectric actuators. The experimental results confirm the excellent performance and robustness of the control system and the very good agreement with the predictions.

This paper considers the RL shunt damping of rotationally periodic structures with an array of regularly spaced piezoelectric patches. The technique is targeted to the damping of a specific mode with n nodal diameters. For this particular case, one can take advantage of the shape of the targeted mode to organize the piezoelectric patches as a modal filter (in parallel loops) which reduces the demand on the inductors of the tuned inductive shunt. In the case of a perfectly rotationally periodic structure, it is possible to organize 4n piezoelectric transducers (PZT patches) in two parallel loops of 2n patches each. In this way, the demand on the inductors is reduced by 4n2 as compared to independent loops, which may allow a fully passive integration of the RL shunt in a turbomachinery application. The method is first illustrated experimentally on a circular plate; it is then applied to a prototype of an industrial bladed drum. The influence of blade mistuning is investigated.

This chapter compares three different ways of mitigating the dynamic response of buildings: Dynamic Vibration Absorber (DVA), Active Mass Damper (AMD) and Hybrid Mass Damper (HMD). The methodology is illustrated with a shear frame example subjected to a random seismic input. Two different ways of implementing the HMD are considered, one called passive starting from a mistuned DVA, and one called active starting from a tuned DVA and using a control system with two feedback loops. It is shown that a well designed HMD may produce performances comparable to that of an AMD while significantly reducing the actuator force and stroke requirements. Besides, the active implementation is immune to control system breakdown, because the HMD is reduced to a properly tuned DVA with optimum performances for a passive system.

This paper addresses the general problem of position control of high precision systems in the face of external disturbances. The paper discusses how the addition of a local force feedback to the control of position actuators can help in achieving a good transmission of the position command in the frequency band of the global position controller, the damping of the flexible modes of the controlled body and the isolation of the controlled body from the vibration of the support. The study is illustrated by a simple numerical model of a flexible structure over an active support.

We discuss the concept of lightweight segmented bimorph mirrors for adaptive optics. The segment consists of a monocrystal silicon substrate actuated by an array of in-plane piezoceramic (PZT) actuators with honeycomb electrodes. We focus on technological aspects of the segment design that are critical for space applications and describe a single segment demonstrator. The morphing capability of the segment is evaluated experimentally. We also discuss the local deformations (dimples) associated with the shape of the electrodes acting on the PZT array.

This paper considers the RL shunt damping of rotationally periodic structures with an array of regularly spaced piezoelectric patches. The technique is targeted to the damping of a specific mode with n nodal diameters. For this particular case, one can take advantage of the shape of the targeted mode to organize the piezoelectric patches in parallel loops, which reduces the demand on the inductors of the tuned inductive shunt. In the case of a perfectly rotationally periodic structure, it is possible to organize 4n piezoelectric transducers (PZT patches) in two parallel loops of 2n patches each. In this way, the demand on the inductors is reduced by 4n(2) as compared to independent loops. The method is first illustrated experimentally on a circular plate; it is then applied to a bladed drum. The influence of blade mistuning is investigated.

This paper discusses the concept of a light weight segmented bimorph mirror for adaptive optics. It focuses on the morphing strategy and addresses the ill-conditioning of the Jacobian of the segments, which are partly outside the optical pupil. Two options are discussed, one based on truncating the singular values and one called damped least squares, which minimizes a combined measure of the sensor error and the voltage vector. A comparison of various configurations of segmented mirrors was conducted; it is shown that segmentation sharply increases the natural frequency of the system with limited deterioration of the image quality.