Tilt corrector based on spring-type magnetostrictive actuators

Abstract

A number of important applications of high precision positioning actuator are related with laser technique and technology, optics, especially with large optical devices for the ground and space based astronomy. These actuators can be used in adaptive optics as the displacement and force actuators to preform in real time a mirror surface, conjugated with the wave front aberration by means of elastic deformation of mirror substratum [1,2]. A spring-type magnetostrictive actuator (STMA) in which Wiedemann effect (WE) [4] is realized, was described in [3] -is one of the interesting types of macro actuators, by means of which it is possible to achieve a precision displacement level 200 Lm with the accuracy of positioning up to 0.1 Lm in a real time scale ( up to 5 ms). Hence, the STMA satisfies all the visible and infrared adaptive optics requirements.A more complete understanding of such approach to actuators creation allows one to establish the main distinguished STMA features [5,6] : 1. High level of STMA relative longitudinal defomatins is controlled by STMA designed parameters and reaches 10 -10 when using ordinary magnetostrictive materials. This level of relative longitudinal deformations is accessible only for best sorts of piezoceramics; 2. A width of STMA magneto mechanical resonant frequencies band (from 10 Hz up to 1 kHz) is controlled by designed STMA parameters; 3. It is possible to use the inverse Wiedemann effect (IWE) for STMA material stresses controlling and, consequently, for closed loop STMA control.Design Guide Analysis of STMA.The WE has been studied in [ 4 , 10 ] . The essence of the WE is the excitation of twisting strains in the ferromagnetic rod while axial and circular magnetizations are created in the rod. Magnetostrictive tensor, which has been used in the [4], didn t describe adequately real phenomena of the WE, because in this work one of the magnetization was considered as exciting twisting and another one -as polarizing the rod material. Equations of the magneto mechanical state of elastic ferromagnetic, for which the function of magneto elastic energy U has minimum, have the following form: bmkulk -H +8cm. = 0 a a a (1) 2 -[iuii]+ 2 a [2 uik(1_Ôik)] + m mk ] = 0 xk Xk i.e., magnetization and deformations vectors components are coupled by O-8194-0609-O/91/$4.OO SPIE Vol. 1500 Innovative Optics and Phase Conjugate Optics(1991) / 93 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx