ABSTRACT The Zernike phase contrast sensor has been studied in the framework of the Active Phasin... more ABSTRACT The Zernike phase contrast sensor has been studied in the framework of the Active Phasing Experiment in the laboratory and on sky at the Very Large Telescope. Atmospheric turbulence strongly affects the shape of the signal of the Zernike phase contrast sensor. The first part of these proceedings is dedicated to a study of the influence of atmospheric turbulence on the signal of the Zernike phase contrast sensor. The second part is dedicated to the phasing of segmented deformable mirrors. A new technology of segmented deformable mirrors for adaptive optics made from silicon wafers with bimorph piezoelectric actuation has been proven to work. A demonstrator with three hexagonal segments of 90 mm corner to corner has been built. The morphing capability of the segmented mirror has been studied and validated by simulations and on a test bench. In this paper, we demonstrate with simulations the phasing of the segmented bimorph mirror with the Zernike phase contrast method. Aspects such as phasing in the presence of segment aberrations have been investigated.
Journal of Intelligent Material Systems and Structures, 2012
This article presents a strategy for enhancing the performance of the synchronized switch damping... more This article presents a strategy for enhancing the performance of the synchronized switch damping on inductor technique used for the semiactive control of structural vibrations. This enhancement is achieved by adding a negative capacitance to the resonant circuit that dissipates the energy converted by a piezoelectric transducer embedded in the structure. A unidimensional spring-mass system shunted synchronously to a resonant circuit is studied analytically, and the main parameters governing the performances of the system are highlighted. Experimental results obtained with a synthetic negative capacitance demonstrate the enhancement of the performance of synchronized switch damping on inductor and confirm the parametric dependencies identified analytically.
The use of tension cables to stiffen and control precision trusses as needed for future interfero... more The use of tension cables to stiffen and control precision trusses as needed for future interferometric missions is investigated. A strategy for damping cable structures with active tendons is presented. Each tendon consists of a displacement actuator (piezoelectric in this case) collocated with a force sensor; the local control law consists of an integral force feedback, which has guaranteed stability if we assume perfect actuator and sensor dynamics. Then an approximate linear theory that allows one to predict the closed-loop poles of a cable structure with a root locus technique is developed; the methodology is applied numerically to a model of the Jet Propulsion Laboratory Micro-Precision Interferometer. Finally, a laboratory experiment on a guyed truss with three active tendons is described, and the experimental results are compared with the numerical predictions.
... All rights reserved. Permissions & Reprints. Spatial filters in structural control. A. Pr... more ... All rights reserved. Permissions & Reprints. Spatial filters in structural control. A. Preumont Corresponding Author Contact Information , E-mail The Corresponding Author , A. François, P. De Man and V. Piefort. ... View Within Article. 4. Spatial aliasing. ...
This paper develops the theory of piezolaminated shells. The fundamental equations governing the ... more This paper develops the theory of piezolaminated shells. The fundamental equations governing the equivalent piezoelectric loads and sensor output are derived. The reciprocity between piezoactuation and piezosensing is pointed out. Piezoelectric shell finite elements are developed based on Mindlin elements. Different electrical boundary conditions are examined.
Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, 2005
The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and... more The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and the influence of structural damping and (b) demonstrate an active damping technique based on collocated actuator/sensor pairs. A numerical stability analysis is performed using the root locus method and it is shown that, along with the structural poles, eigenvalues due to the delay parameter may contribute to instability. Since experimental demonstration of chatter in real machines is difficult, an alternative way of demonstration via a mechatronic simulator is presented, using the ‘hardware-in-the-loop’ concept. The mathematical model of the regenerative cutting process in turning is simulated in a computer and this is interfaced to a beam, representing the structural dynamics of the machine, via a displacement sensor and force actuator. In this way, a hardware and a software loop are combined. In a second step, an additional control loop is added, consisting of an accelerometer sensor...
This paper discloses a stiff active interface wherein a six degree of freedom Stewart platform, a... more This paper discloses a stiff active interface wherein a six degree of freedom Stewart platform, a standard hexapod with a cubic architecture, is used to actively increase the structural damping of flexible systems attached to it. It can also be used to rigidly connect arbitrary substructures while damping them. Each leg of the active interface consists of a linear piezo
Hovering flapping flight is inherently unstable and needs to be stabilized actively. We present a... more Hovering flapping flight is inherently unstable and needs to be stabilized actively. We present a control mechanism that modulates independently the wing flapping amplitude and offset by displacing joints of a flapping linkage mechanism. We demonstrate its performance by high speed camera recordings of the wing motion as well as by direct measurements of pitch moment and lift force. While flapping at 17 Hz the prototype produces 90 mN of lift and generates pitch moments from −0.7 N.mm to 1.1 N.mm. The mechanism shows low level of cross-coupling in combined pitch and roll commands.
This paper is concerned with the extrapolation of the active optics of current 10-meter class tel... more This paper is concerned with the extrapolation of the active optics of current 10-meter class telescopes (Keck, VLT) to the next generation of 30 m to 40 m Extremely Large Telescopes (ELT). Using the scaling laws for the structural response and the control requirements, the paper shows that the current baseline design of ELT is likely to bring a strong control-structure interaction, which could deteriorate significantly the image quality. Two options are discussed to alleviate this situation: (1) building the support structure in a material with high specific modulus, like for example carbon reinforced composites, and (2) enhancing the structural damping, possibly by active means. This discussion is intended to be generic rather than targeted to a specific telescope.
This paper describes a non contacting measurement technique for the transverse vibration of small... more This paper describes a non contacting measurement technique for the transverse vibration of small cables and strings using an analog position sensing detector. On the one hand, the sensor is used to monitor the cable vibrations of a small scale mock-up of a cable structure in order to validate the nonlinear cable dynamics model. On the other hand, the optical sensor is used to evaluate the performance of an active tendon control algorithm with guaranteed stability properties. It is demonstrated experimentally, that a force feedback control law based on a collocated force sensor measuring the tension in the cable is feasible and provides active damping in the cable.
ABSTRACT The Zernike phase contrast sensor has been studied in the framework of the Active Phasin... more ABSTRACT The Zernike phase contrast sensor has been studied in the framework of the Active Phasing Experiment in the laboratory and on sky at the Very Large Telescope. Atmospheric turbulence strongly affects the shape of the signal of the Zernike phase contrast sensor. The first part of these proceedings is dedicated to a study of the influence of atmospheric turbulence on the signal of the Zernike phase contrast sensor. The second part is dedicated to the phasing of segmented deformable mirrors. A new technology of segmented deformable mirrors for adaptive optics made from silicon wafers with bimorph piezoelectric actuation has been proven to work. A demonstrator with three hexagonal segments of 90 mm corner to corner has been built. The morphing capability of the segmented mirror has been studied and validated by simulations and on a test bench. In this paper, we demonstrate with simulations the phasing of the segmented bimorph mirror with the Zernike phase contrast method. Aspects such as phasing in the presence of segment aberrations have been investigated.
Journal of Intelligent Material Systems and Structures, 2012
This article presents a strategy for enhancing the performance of the synchronized switch damping... more This article presents a strategy for enhancing the performance of the synchronized switch damping on inductor technique used for the semiactive control of structural vibrations. This enhancement is achieved by adding a negative capacitance to the resonant circuit that dissipates the energy converted by a piezoelectric transducer embedded in the structure. A unidimensional spring-mass system shunted synchronously to a resonant circuit is studied analytically, and the main parameters governing the performances of the system are highlighted. Experimental results obtained with a synthetic negative capacitance demonstrate the enhancement of the performance of synchronized switch damping on inductor and confirm the parametric dependencies identified analytically.
The use of tension cables to stiffen and control precision trusses as needed for future interfero... more The use of tension cables to stiffen and control precision trusses as needed for future interferometric missions is investigated. A strategy for damping cable structures with active tendons is presented. Each tendon consists of a displacement actuator (piezoelectric in this case) collocated with a force sensor; the local control law consists of an integral force feedback, which has guaranteed stability if we assume perfect actuator and sensor dynamics. Then an approximate linear theory that allows one to predict the closed-loop poles of a cable structure with a root locus technique is developed; the methodology is applied numerically to a model of the Jet Propulsion Laboratory Micro-Precision Interferometer. Finally, a laboratory experiment on a guyed truss with three active tendons is described, and the experimental results are compared with the numerical predictions.
... All rights reserved. Permissions & Reprints. Spatial filters in structural control. A. Pr... more ... All rights reserved. Permissions & Reprints. Spatial filters in structural control. A. Preumont Corresponding Author Contact Information , E-mail The Corresponding Author , A. François, P. De Man and V. Piefort. ... View Within Article. 4. Spatial aliasing. ...
This paper develops the theory of piezolaminated shells. The fundamental equations governing the ... more This paper develops the theory of piezolaminated shells. The fundamental equations governing the equivalent piezoelectric loads and sensor output are derived. The reciprocity between piezoactuation and piezosensing is pointed out. Piezoelectric shell finite elements are developed based on Mindlin elements. Different electrical boundary conditions are examined.
Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, 2005
The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and... more The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and the influence of structural damping and (b) demonstrate an active damping technique based on collocated actuator/sensor pairs. A numerical stability analysis is performed using the root locus method and it is shown that, along with the structural poles, eigenvalues due to the delay parameter may contribute to instability. Since experimental demonstration of chatter in real machines is difficult, an alternative way of demonstration via a mechatronic simulator is presented, using the ‘hardware-in-the-loop’ concept. The mathematical model of the regenerative cutting process in turning is simulated in a computer and this is interfaced to a beam, representing the structural dynamics of the machine, via a displacement sensor and force actuator. In this way, a hardware and a software loop are combined. In a second step, an additional control loop is added, consisting of an accelerometer sensor...
This paper discloses a stiff active interface wherein a six degree of freedom Stewart platform, a... more This paper discloses a stiff active interface wherein a six degree of freedom Stewart platform, a standard hexapod with a cubic architecture, is used to actively increase the structural damping of flexible systems attached to it. It can also be used to rigidly connect arbitrary substructures while damping them. Each leg of the active interface consists of a linear piezo
Hovering flapping flight is inherently unstable and needs to be stabilized actively. We present a... more Hovering flapping flight is inherently unstable and needs to be stabilized actively. We present a control mechanism that modulates independently the wing flapping amplitude and offset by displacing joints of a flapping linkage mechanism. We demonstrate its performance by high speed camera recordings of the wing motion as well as by direct measurements of pitch moment and lift force. While flapping at 17 Hz the prototype produces 90 mN of lift and generates pitch moments from −0.7 N.mm to 1.1 N.mm. The mechanism shows low level of cross-coupling in combined pitch and roll commands.
This paper is concerned with the extrapolation of the active optics of current 10-meter class tel... more This paper is concerned with the extrapolation of the active optics of current 10-meter class telescopes (Keck, VLT) to the next generation of 30 m to 40 m Extremely Large Telescopes (ELT). Using the scaling laws for the structural response and the control requirements, the paper shows that the current baseline design of ELT is likely to bring a strong control-structure interaction, which could deteriorate significantly the image quality. Two options are discussed to alleviate this situation: (1) building the support structure in a material with high specific modulus, like for example carbon reinforced composites, and (2) enhancing the structural damping, possibly by active means. This discussion is intended to be generic rather than targeted to a specific telescope.
This paper describes a non contacting measurement technique for the transverse vibration of small... more This paper describes a non contacting measurement technique for the transverse vibration of small cables and strings using an analog position sensing detector. On the one hand, the sensor is used to monitor the cable vibrations of a small scale mock-up of a cable structure in order to validate the nonlinear cable dynamics model. On the other hand, the optical sensor is used to evaluate the performance of an active tendon control algorithm with guaranteed stability properties. It is demonstrated experimentally, that a force feedback control law based on a collocated force sensor measuring the tension in the cable is feasible and provides active damping in the cable.
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