Servo-fluid-elastic modeling of contactless levitated adaptive secondary mirrors

Abstract

The paper develops a comprehensive approach for the servo-fluid-elastic modeling of electromagnetically levitated secondary adaptive mirrors. The system modeling includes the mirror structural dynamics model, its interaction with the fluid film interposed between the mirror and its reference backplate and disturbances due to local air turbulence. The accuracy of the proposed fluid dynamic model is assessed by comparing it with a significant sample of high fidelity 3D Navier-Stokes analyses. The simulation tool is then used to demonstrate the effectiveness and robustness of a recently proposed control, based on a system dynamics cancellation and an iterated steady state feedforward contribution. The simulations clearly highlights the improvements achievable implementing the new control scheme.

Self-Tuning Mechanism for the Design of Adaptive Secondary Mirror Position Control

“…The latter, in fact, has been introduced with the only purpose of providing some simple and intuitive motivations for the considered control architecture. Clearly, to capture the complete dynamical behavior of the DM, more elaborated models would be needed (see [34], [35], and the references therein). Nonetheless, similar conclusions concerning the control law (1) could be drawn even when the behavior of the shell is described by the general dynamic equation of a thin plate [34].…”

Completely, partially centralized and fully decentralized control schemes of large adaptive mirrors

“…The system model is rather complex and involves a multiphysics description (see Figure 2) of the static and dynamic behavior of the deformable mirror, the air squeeze film (30-110 mm) interposed between the mirror and the reference plate, sensors and actuators, the signal A/D/A conversions including quantization errors, noises, delays and the wind turbulence directly impinging on the mirror surface as an external disturbance. A complete and detailed description of the model, along with numerical/experimental correlations can be found in previous works (Manetti et al, 2010(Manetti et al, , 2012a.…”

“…A simplified turbulence disturbance approximation is proposed by Manetti et al (2012a); within the present work the disturbance is considered fully correlated over the mirror surface and the turbulence velocity time history is obtained through a first-order rational approximation of its von Karman power spectrum. The Gemini Telescope experimental measurements (Smith, 2001) suggest a turbulence average velocity of 7.5 m/s and a velocity standard deviation of 2 m/s.…”

“…Hence, a reasonable model of its effects is mandatory to obtain a realistic prediction of the system stability and performances. The simulator includes a fluid dynamics description which exploits an ad hoc two-dimensional formulation based on a finite volume discretization of the Navier-Stokes equations (Manetti et al, 2012a). Its coupling to the structural motion is obtained through the interpolation provided by X f .…”

Self-Tuning Shape Control of Massively Actuated Adaptive Mirrors

“…1 the image residual wavefront aberrations are measured by the wavefront sensor, the optical controller elaborates the optimal shape command to compensate for image distortion and the adaptive mirror tracks the required shapes [1]. model and of an enhanced controller can be found in [2], [3], [4]. The control law proposed in the above mentioned papers is based on already working solutions, such as the Multiple Mirror Telescope (MMT) [5] and the Large Binocular Telescope (LBT) [6].…”