Control of a deformable mirror subject to structural disturbance
03 Apr 2008-Vol. 6971
TL;DR: In this paper, a wavefront control method for the Naval Postgraduate School adaptive optics testbed is developed to remove structural noise from the flexible optical surface using discrete time proportional integral control with second order filters.
Abstract: Future space based deployable telescopes will be subject to non-atmospheric disturbances. Jitter and optical misalignment on a spacecraft can be caused by mechanical noise of the spacecraft, and settling after maneuvers. The introduction of optical misalignment and jitter can reduce the performance of an optical system resulting in pointing error and contributing to higher order aberrations. Adaptive optics can be used to control jitter and higher order aberrations in an optical system. In this paper, wavefront control methods for the Naval Postgraduate School adaptive optics testbed are developed. The focus is on removing structural noise from the flexible optical surface using discrete time proportional integral control with second order filters. Experiments using the adaptive optics testbed successfully demonstrate wavefront control methods, including a combined iterative feedback and gradient control technique. This control technique results in a three time improvement in RMS wavefront error over the individual controllers correcting from a biased mirror position. Second order discrete time notch filters are also used to remove induced low frequency actuator and sensor noise at 2Hz. Additionally a 2 Hz structural disturbance is simulated on a Micromachined Membrane Deformable Mirror and removed using discrete time notch filters combined with an iterative closed loop feedback controller, showing a 36 time improvement in RMS wavefront error over the iterative closed loop feedback alone.
Citations
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04 Jan 2016
7 citations
TL;DR: A practical controller design method is proposed which significantly reduces the system dimension for a system where the dimension required to represent the dynamics of the plant is much smaller than the dimension of the full plant model.
Abstract: For a large adaptive optics system such as a large segmented mirror telescope SMT, it is often difficult, although not impossible, to directly apply common multi-input multi-output MIMO controller design methods due to the computational burden imposed by the large dimension of the system model. In this article, a practical controller design method is proposed which significantly reduces the system dimension for a system where the dimension required to represent the dynamics of the plant is much smaller than the dimension of the full plant model. The proposed method decouples the dynamic and static parts of the plant model by a modal decomposition technique to separately design a controller for each part. Two controllers are then combined using the so-called sensitivity decoupling method so that the resulting feedback loop becomes the superposition of the two individual feedback loops of the dynamic and static parts. A MIMO controller was designed by the proposed method using the H∞ loop-shaping technique for an SMT model to be compared with other controllers proposed in the literature. Frequency-domain analysis and time-domain simulation results show the superior performance of the proposed controller.
6 citations
Cites methods from "Control of a deformable mirror subj..."
...Zernike polynomial had been commonly used to form a set of modes, or a basis, in AO (Allen 2007; Allen, Kim, and Agrawal 2008), but other modes have been proposed recently such as singular value decomposition (SVD) modes (Gibson, Chang, and Chen 2001), frequency-weighted modes (Liu and Gibson 2007;…...
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TL;DR: In this paper, the authors studied geometry adaptive control for a GFRC reflector with piezoelectric ceramic transducer (PZT) actuators assembled on the ribs.
Abstract: Maintaining geometrical high precision for a graphite fiber reinforced composite (GFRC) reflector is a challenging task. Although great efforts have been placed to improve the fabrication precision, geometry adaptive control for a reflector is becoming more and more necessary. This paper studied geometry adaptive control for a GFRC reflector with piezoelectric ceramic transducer (PZT) actuators assembled on the ribs. In order to model the piezoelectric effect in finite element analysis (FEA), a thermal analogy was used in which the temperature was applied to simulate the actuation voltage, and the piezoelectric constant was mimicked by a Coefficient of Thermal Expansion (CTE). PZT actuator’s equivalent model was validated by an experiment. The deformations of a triangular GFRC specimen with three PZT actuators were also measured experimentally and compared with that of simulation. This study developed a multidisciplinary analytical model, which includes the composite structure, thermal, thermal deformation and control system, to perform an optimization analysis and design for the adaptive GFRC reflector by considering the free vibration, gravity deformation and geometry controllability.
5 citations
Additional excerpts
...-4 WAWA considerably less attention has been focused on the use of smart structures for shape control.(23,24) This paper will describe a new architecture of adaptive GFRC reflector....
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10 Feb 2011
TL;DR: In this paper, a 3-meter diameter space telescope testbed with six segments that uses an AHM technology was used for surface control of the primary mirror using adaptive optics and a MEMS deformable mirror was used to improve the performance of the NPS segmented mirror telescope.
Abstract: Development of space telescopes, such as the Hubble Space Telescope and the James
Webb Telescope has been very challenging in terms of cost, schedule, and performance.
For several future space missions, larger aperture and lightweight deployable mirrors, in
the range of 10-20 meters in diameter with high surface accuracy, are required. In order
to achieve lightweight, reduce cost for development and provide performance robustness,
actuated hybrid mirror (AHM) technology is under development. The Naval
Postgraduate School (NPS) recently received a 3-meter diameter space telescope testbed
with six segments that uses an AHM technology. This paper will discuss the work
performed at NPS on the surface control of the primary mirror using adaptive optics. This
paper will also discuss how we can use a MEMS deformable mirror to improve the
performance of the NPS segmented mirror telescope. The high-stroke, high-order
actuated MEMS deformable mirror will correct the residual alignment and surface errors
that are not corrected by the actuators on the mirrors. The mirror will use electrostatic
actuation to eliminate the need for power to hold its position and will be capable of open-loop,
go-to positioning.
3 citations
Cites background or methods from "Control of a deformable mirror subj..."
...Amplitude of 54 Volts sinusoidal signal is added on Actuator 10 [2] Figure 6 shows the experimental results for the RMS wave front error for a 5 Hz disturbance with integral control with integral and notch filters....
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...The Spacecraft Research and Design Center (SRDC) at the Naval Postgraduate School has an active research program [2] in adaptive optics and controls for active surface space mirrors....
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...The control system [2,3] is shown in Fig....
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18 Aug 2008
TL;DR: In this article, two optical beam control testbeds were developed at the Spacecraft Research and Design Center, Naval Postgraduate School, to evaluate and develop control techniques for jitter and adaptive optics control.
Abstract: : This paper discusses two optical beam control testbeds developed at the Spacecraft Research and Design Center, Naval Postgraduate School, to evaluate and develop control techniques for jitter and adaptive optics control. The first testbed, a Jitter Control Testbed is used to develop control techniques for optical beam jitter. In the second testbed, the Adaptive Optics Testbed, adaptive optics control techniques are used to control the surfaces of a segmented mirror with the objective of minimizing aberrations in the images. This paper will also discuss the evaluation of different control techniques used in jitter and adaptive optics control.
3 citations
References
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TL;DR: In this paper, the problem of wavefront estimation from wave-front slope measurements has been examined from a least-squares curve fitting model point of view, and a new zonal phase gradient model is introduced and its error propagator, which relates the mean square wavefront error to the noisy slope measurements, has been compared with two previously used models.
Abstract: The problem of wave-front estimation from wave-front slope measurements has been examined from a least-squares curve fitting model point of view. It is shown that the slope measurement sampling geometry influences the model selection for the phase estimation. Successive over-relaxation (SOR) is employed to numerically solve the exact zonal phase estimation problem. A new zonal phase gradient model is introduced and its error propagator, which relates the mean-square wave-front error to the noisy slope measurements, has been compared with two previously used models. A technique for the rapid extraction of phase aperture functions is presented. Error propagation properties for modal estimation are evaluated and compared with zonal estimation results.
958 citations
TL;DR: An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels.
Abstract: The nonlinear response and strong coupling of control channels in
micromachined membrane deformable mirror (MMDM) devices make it
difficult for one to control the MMDM to obtain the desired mirror
surface shapes. A closed-loop adaptive control algorithm is
developed for a continuous-surface MMDM used for aberration
compensation. The algorithm iteratively adjusts the control
voltages of all electrodes to reduce the variance of the optical wave
front measured with a Hartmann–Shack wave-front sensor. Zernike
polynomials are used to represent the mirror surface shape as well as
the optical wave front. An adaptive experimental system to
compensate for the wave-front aberrations of a model eye has been built
in which the developed adaptive mirror-control algorithm is used to
control a deformable mirror with 19 active channels. The
experimental results show that the algorithm can adaptively update
control voltages to generate an optimum continuous mirror surface
profile, compensating for the aberrations within the operating range of
the deformable mirror.
158 citations
07 Nov 2002
TL;DR: In this paper, a design for an adaptive optics system that utilizes modern H/sub /spl infin// control theory to optimize the robustness of the system is presented for real-time correction of blurred images and have applications in astronomical imaging, freespace optical communications and high-energy laser beam guidance.
Abstract: Adaptive optics systems are concerned with the real-time correction of blurred images and have applications in astronomical imaging, freespace optical communications and high-energy laser beam guidance. This paper outlines the proposed design for an adaptive optics system that utilizes modern H/sub /spl infin// control theory to optimize the robustness of the system.
16 citations
TL;DR: In this article, a two-section open stub is employed to emulate a notch filter in the discrete-time domain, and a cascade connection of two-sections open stubs with proper frequency scaling serves to represent a bandstop filter of wider stopband bandwidth.
Abstract: A new method for the design of a bandstop filter is presented. The two-section open stub is employed to emulate a notch filter in the discrete-time domain. A cascade connection of two-section open stubs with proper frequency scaling serves to represent a bandstop filter of wider stopband bandwidth. Experimental results are presented to illustrate the validity of this design method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1098–1101, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22356
2 citations