Research On The Ion Beam Figuring Technology

The development of optical system has increased the requirements for high-precision optical surfaces. At present, the contact figuring methods are limited to obtaining optical surfaces with accuracies down to the nanometer or sub-nanometer level due to the wear tool, edge effects, and load press. Ion beam figuring (IBF) avoids these problems because of non-contact figuring. More attention has been paid to this technology during the past two decades. The principle of IBF is that the computer controlled five axis moving system moves an ion beam source according to a predefined scanning path and computed dwell time on the optical surface, and the desired removal amounts can be removed by sputtering between the ion beam and the optical material. When the ion beam source is stable and the five-axis moving system is high precision, the desired removal amounts can be expressed as the convolution operation of dwell time function and ion beam removal function. .The major works of this paper are summarized as follows:(1). To get a high-precision optical surface, the de-convolved process of dwell time was transferred to a matrix equation in which the damped factor and the extra removal amount were introduced to expand the freedom of solution. A path weight factor and a surface error weight factor were used to take the scanning path and the initial surface error into account. Combined with the Gerchberg band-limited extrapolation algorithm for initial surface error map extension, perfect dwell time solution can be obtained and the high precision surface could be obtained within full aperture range.(2). Using an analysis of the location errors, we proposes that the final figure errors caused by the location errors of the ion source of five axis motion subsystem could be attributed to a coefficient factor. The best way to design the location precision is to take both the ion beam material removal function and the location errors into account simultaneously.(3). A controlled model of ion beam iteration figuring (IBIF) is proposed, and the simulation results show that the damped weight factor W and the ion beam diameter d are the most important parameter in ion beam figuring (IBF) process. We gives how to select the right W and d so that the IBF process meet the requirement of finished figure error precision and have quicker figure convergence speed and smaller extra removal amount and shorter figuring cost time.(4). To reduce the adverse influence of hot deformation caused by long figuring time, the genetic algorithm is introduced to the figuring scan path arrangement. By decrease a little figure precision, the figuring time can be reduce to half of the form figuring time, this method is helpful for the figuring time control in the real ion beam figuring process.(5). An experiment was design to research the roughness of optical surface as a function of ion beam incident angle. An new figuring method was proposed to improve the roughness deteriorate when ion beam incident by 90 degree across the optical surface.