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18 April 2008 Membrane reflectors with variable area electrostatic actuation for laser beam guidance
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Abstract
The following is an investigation into the dynamic behavior of small deformable mirrors based on thin, metallized membranes. Focusing on providing a predetermined focus/defocus correction to a beam, as well as producing specified angular deflections of the beam in the vertical and horizontal planes. Directing the mirrored surface is accomplished using electrostatic actuation. Current designs are comprised of 3 actuator pads fabricated on a fiber reinforced plastic substrate that drive a metallized kapton membrane, which is separated from the substrate by spacers that provide a known air gap. A previous paper[3] consisted of a variable area actuation strategy that would only allow membrane deflection of 1/3 the total gap size before incurring instability due to "snap down". Addressed here is the proingblem of extend the control strategy into the deflection regime where the full nonlinear model must be used for the actuation force. A solution to this problem is an extended controller that can handle the full deflection range of the 40m air gap between the charged electrodes on the fixed substrate and the movable metallized reflective membrane. The observer for the control system operates in continuous time mode. Although the discrete area approximation is also shown alongside, only the continuous-area approximation is studied here. From the continuous-area approximation it is easily seen that the open loop system would be unstable, while the closed loop system closely follows the desired reference specification (maximum deflection approaching 40m, and bandwidth approaching 500 Hz).
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Miles A. Wickersham, Andrew W. Downs, Nicolas Kingsbury, and Umesh A. Korde "Membrane reflectors with variable area electrostatic actuation for laser beam guidance", Proc. SPIE 6928, Active and Passive Smart Structures and Integrated Systems 2008, 69281Q (18 April 2008); https://doi.org/10.1117/12.771320
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