Design of a Fast Long Range Actuator - FLORA II

Abstract

The objective of this research was to develop a new way of machining Non-Rotationally Symmetric (NRS) surfaces. NRS optical surfaces have traditionally been machined using very slow spindle speeds and actuators with a range on the order of hundreds of microns. This meant that a very long time was required in order to achieve a high quality NRS optical surface. A Fast Long Range Actuator (FLORA I) has already been constructed at NC State University’s Precision Engineering Center with a goal of machining NRS surfaces with a sag of ± 2 mm at 20 Hz. For the surface to have the same quality as conventional diamond turning machines the surface must have a form error of less than 150 nm peak to valley and a surface finish of 5 nm RMS.

The existing FLORA I system consist of a triangular aluminum honeycomb piston supported by orifice type air bearings and driven by a linear motor. While machining with FLORA I has had success, the system package is large when compared with the size and path of the diamond tool. FLORA I has an observed spurious 200 nm vertical vibration which has an adverse impact when machining precision surfaces.

Therefore, the goal of the research presented in this thesis is a new actuator (FLORA II) designed to address the limitations of its predecessor. The FLORA II package will be smaller and lighter than FLORA I while maintaining air bearing stiffness and improving system dynamics. This will be accomplished through structural mechanics and dynamic analysis using computer simulation supplemented with experimental testing and validation. The procedure described in this thesis will allow the FLORA II to produce high quality NRS optical surfaces from a small, lightweight system.