Abstract

The first prototype of an actuator for a new adaptive deformable mirror (DM) is presented together with the development of a 61-actuator grid element. The DM design consists of a thin membrane which acts as the correcting element. A grid of low voltage electro-magnetical push-pull actuators, impose out-of-plane displacements in the mirror's membrane. To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added. Several variants of variable reluctance actuators are considered. Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) provides a static magnetic force attracting ferromagnetic material. By applying a current through a coil which is situated around this magnet, this force can be influenced. Depending on the mechanical stiffness of the actuator, this leads to a certain displacement. Both the PM and the coil are connected to the fixed world and only the ferromagnetic material will move. The actuators are produced in arrays which make the design easy and extendable. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. The paper describes how the actuator stiffness and efficiency can be controlled. A test-setup is developed in which the actuator characteristics are measured.

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