Segmented bimorph mirrors for adaptive optics: morphing strategy

Abstract

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.

Shape Control of a Unimorph Deformable Mirror for Space Active Optics under Uncertainties

“…This section gives a review of the framework for the quasi-static control of the shape of a piezoelectric deformable mirror [ 21 ], which is unimorphly controlled by a set of strain actuators, the driving voltages are fed to the patterned electrodes with a certain shape formed. The structural dynamic equation with respect to a discrete Degree-of-Freedom (DoF) of the mirror surface can be written by where M , C , and K are the inertial, damping, and stiffness matrices of the mirror structure, respectively, is the morphing forces driven by unimorph strain actuators, in which is the vector of actuator inputs (voltages), and stands for the matrix relating the input voltages to the equivalent piezoelectric forces acting on the mirror.…”

“…This section gives a review of the framework for the quasi-static control of the shape of a piezoelectric deformable mirror [21], which is unimorphly controlled by a set of strain actuators, the driving voltages are fed to the patterned electrodes with a certain shape formed. The structural dynamic equation with respect to a discrete Degree-of-Freedom (DoF) q of the mirror surface can be written by…”

Segmented bimorph mirrors for adaptive optics: segment design and experiment

“…8). The target surface has the shape of a simulated turbulent screen representative of the VLT telescope (also used in [8]); however, in order to reduce the effect of noise in the control electronics, the global amplitude has been magnified by 8.75 to achieving a peak to valley (PV) of 23 μm, in order to exploit the full dynamics of the voltage amplifiers. Figure 9(a) shows the target shape of segment no.…”

“…A concept of a scalable segmented bimorph mirror (strictly speaking, it is a monomorph, since there is a single active layer) has been proposed to provide a large number of degrees of freedom while preserving the advantages of low cost, low mass, and robustness of bimorph mirrors and overcoming the problem of a low resonance mode [5,6]. The morphing capability of the concept was addressed in [7], and the morphing strategy was analyzed more recently in [8]. This paper further discusses technological aspects of the segment design especially related to space applications and reports on experiments performed on a segment prototype (Fig.…”

Using the ferroelectric/ferroelastic effect at cryogenic temperatures for set-and-hold actuation

“…The electromechanical coupling behavior of ferroelectric materials has widespread applications to the field of adaptive structures. Active mirrors for telescopes [1][2][3][4][5][6], adjustable reflectors for spacecraft communication [7], and adaptive aircraft wings [8] are examples of such applications. In particular, ceramic-based actuators are often utilized due to the combination of their large actuation strains and high stiffness.…”