Abstract Details
| Name: Shrishail Raut Affiliation: Pandit Deendayal Petroleum University Conference ID: ASI2016_533 Title : Modelling of warping forces for non-axial aspheric profile of thin mirror and a case study on cross coupling of warping forces on surface deformation. Authors and Co-Authors : S.Sriram, IIAP P.K.Mahesh, IIAP Dr. Vineeth Valsan, IIAP Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : The TMT primary mirror is made of 492 hexagonal non axial-symmetric (aspherical shape) off-axis segments, each having a size of 1.44 m across corners. The TMT project prefers to utilize Stressed Mirror Polishing (SMP) of circular mirror blanks followed by hex-cutting, mounting onto a support system, and finally, Ion Beam Figuring (IBF). The SMP method has been proven to be the fastest and lowest cost polishing method for large aspherical mirror segments. Stress mirror polishing technique involves majorly optical-mechanical process in fabrication of mirror segments. In general, the idea is to apply an appropriate set of forces to a mirror blank so that after a sphere has been ground and polished into the blank, the forces can be removed, and the polished spherical surface deforms elastically into the desired non-axisymmetric surface. The thin mirror is modelled and analysed using NX Nastran. The set of warping forces applied on the thin mirror are generated depending upon the optical terms. The nodal displacement values of the mirror surface are further exported to MatLab software. Zernike coefficients of various optical terms and the simulated deformed mirror surface are generated in MatLab. Zernike coefficients obtained are compared with the corresponding theoretical values. Combinations for various optical terms are taken and analysed for any cross-coupling. We will be also taking single optical term at a time, the reason being that, so as to obtain the value of forces that are required to re-stress the mirror in order to obtain the desired value of the optical term at a time. The results of these simulation and modelling are discussed in this paper. |