The splicing sub mirrors of the Thirty Meter Telescope(TMT) primary mirror are off-axis aspheric shapes with large aspheric value. In order to reduce the time of stressed mirror annular polishing(SMAP), the mirror surface will be fine grinding using computer numerical control (CNC) processing device based on a six axis robotic arm before SMAP process, and the segment mirror will be lapping quickly benefit by high removal efficiency of fine grinding compared to polishing. In this article the principles of CNC processing, robotic arm motion controlling, and the experiment of fine grinding removal function are introduced. Finally, the segment mirror of TMT at the out edge is processed, and the fabrication convergence curve and final surface residual distribution are obtained. The optimized machining experience can further shorten the processing time and be used for early aspheric process of segments.
Abrasive water jet processing technology is a processing method developed in recent decades using highenergy beams, which is suitable to removal and processing different materials, because its processing process has its own cooling effect and has incomparable advantages in other processing methods. Process studies involving multiple materials in the same area have not been reported. In this paper, the influence of abrasive water jet processing technology parameters on the removal rate of different materials in a small area is studied experimentally, and the removal rate of high-purity quartz glass, doped quartz glass and epoxy resin adhesive layer is tested by single factor and orthogonal test method. Experiments show that within a certain range of process parameters, jet pressure, nozzle diameter and nozzle height have obvious effects on the removal rate, while abrasive particle size have the lowest impact. Experiments are used to derive optimal process parameters for simultaneous removal of different materials.
In this article, the measurement method of convex hyperboloid using Hindle sphere is further studied. Firstly, the precise analytical formulas for solving radius of curvature, the diameters of outer edge and inner hole of Hindle sphere mirror are developed. The formula can be degenerated to the common approximate formula under certain conditions. In addition, the semi exact analytical formulas for solving the parameters of auxiliary Hindle sphere mirror are derived under some conditions, and the approximate formula is further extended to other occasions of aspheric mirror test, and a feasible stitching detection scheme for the secondary mirror of the CFGT (China Future Giant Telescope) is given. Then, based on the aberration theory, using Hindle auxiliary sphere, the relationships and formulas of the measurement error of vertex radius of curvature of convex hyperboloid mirror caused by the adjustment of interferometer position, the mirrors spacing, and machining error of radius of curvature of the Hindle sphere mirror are obtained, and the Zemax optical software is used for simulation verification.
The primary mirrors of several large ground-based astronomical telescopes currently in the research or planning phases, such as TMT (Thirty Meter Telescope), ELT(Extremely Large Telescope) and LOT (Large Optical /infrared Telescope), take the form of a segmented array telescope. The fabrication of hundreds of off-axis aspheric segments is one of the key technologies for their development. Our proposed stressed mirror continuous polishing (SMCP) method combines the stressed mirror polishing (SMP) and continuous polishing (CP) technologies. The combined technologies deliver high-quality surface smoothness of the SMP technique with the high efficiency of continuous polishing. Nanjing Institute of Astronomical Optics & Technology (NIAOT) and TMT have carried out in-depth cooperation in the segment fabrication of the primary mirror. NIAOT is currently working on the development of off-axis aspheric segments. In this article, the progress for the 5m continuous polishing machine and ancillary equipment, the stress loading test on a 1.52 meter segment, the calibration of our 2-dimensional contact-metrology device and the reference mirror calibration are introduced here in detail.
Indoor air turbulence had a certain degree of influence on optical testing or optical system image quality. A long optical testing path was built in tower which was one of the largest vertical towers for optical testing in China with about 23-meter high. The relevant influence characteristics were measured and studied in a specific state. First, the air turbulence was formed using air conditionings. Then, the optical wave fronts were sampled by interferometer with two conditions of undisturbed situation and disturbed situation in which the air conditioners were turned on for a while and then turned off some time and sampling was beginning. After the statistical analyzing to the sampling results, the following several evaluation results of image quality were acquired in different status, the Radius of Encircled 80% Energy (REE), the evaluation factor of modulation transfer function (MTF), the Strehl Ratio (SR), the traditional evaluation method PV/RMS value of wave fronts, and the turbulent correlation length of atmospheric r0. The statistical calculation results showed that turbulence intensity increased and optical image quality was deteriorated after air disturbed.
The research works are summarized for Φ1.1m off-axis aspheric segments which are scaled-down TMT segments polished by NIAOT using SMAP (Stressed Mirror Annular Polishing) method in the previous phase and testing preparations for 1.45m mirrors. The detailed introduction is given on result of errors analysis in contact detection testing of segments. In the second part, the selected basis of sampling number for contact-type detector arrays and the terms number of Zernike polynomials we need are studied. And the situations on orthogonality destruction of Zernike polynomials in discrete points sampling case and spectral analysis for each order Spherical aberrations in continuous sampling are introduced.
A new type Stressed Mirror Polishing method using annular polishing machine is developed in NIAOT. It provides good efficiency for the massive production of off-axis segments for the extremely large telescope because 3 or more pieces of segment can be polished simultaneously on a AP machine. With an annular polishing machine with 3.6m diameter, two scale-down TMT segments have been polished. Both 2 segments are Φ1100mm in diameter, with the vertex radius of curvature of 60m and aspheric constant K=-1.000953. The off-axis distances (OAD) are 8m and 12m respectively. After SMAP process, the acceptable surface accuracy can be reached, which is 1.12μm/0.23μm of PV/RMS value for the segment with 8m OAD, and 1.22 μm/0.26 μm for another one.
The test method of Large-diameter convex secondary mirror in development process is the key to making large
telescope technology. Classical means HINDLE to test using of non - aberration points needs a spherical reflecting
mirror which larger than the secondary mirror several times. This new Hindle test method based on stitching
technology can significantly reduce their standard mirror's size, drop the difficulty of processing and cut down the
costs. In This paper, the Hindle testing basic principles which base on stitching technology is introduced firstly, then
principle of stitching and least square method. Following the parameters of inside and outside standard mirrors are
derived. Then translation and rotation transformation algorithm of different sub-aperture interferometer array data is
given. Finally the preliminary results of the radial stitching experiments are given. The results showed that the relative
error is RMS = 6.1%, PV = 5.11%. With improving and perfection, this method can be used in the E-ELT, CFGT
convex secondary mirror telescope test.
Nanjing Institute of Astronomical Optics & Technology (NIAOT) is investigating two types of sub-aperture polish
technique for manufacturing aspheric components in large astronomical telescopes. One technique is computer
controlled optical surfacing (CCOS). It removes material by a small polish tool through traditional mechanical and
chemical process. The other is ion beam figuring (IBF) technique. It employs a neutralized ion beam to physically
sputter material form optical surface. Although the basic mechanism of the two techniques is different, they true share
the same mathematical model and fabrication diagram which will be put forward firstly in this paper. Then tool design
and material removal function in CCOS will be studied following by a fabrication instance using CCOS. After that some
recent progresses achieved in IBF is presented. The last part will focus on the complementary relationship of CCOS and
IBF. Using them alternatively optimal combination of surface precision, efficiency and edge control could be obtained.
Simulation is provided to support this view and experiment will be done in near future.
During operation, astronomical telescope will undergo thermal disturbance, especially more serious in solar telescope,
which may cause degradation of image quality. As drives careful thermal load investigation and measure applied to
assess its effect on final image quality during design phase. Integrated modeling analysis is boosting the process to find
comprehensive optimum design scheme by software simulation. In this paper, we focus on the Finite Element Analysis
(FEA) software-ANSYS-for thermal disturbance analysis and the optical design software-ZEMAX-for optical system
design. The integrated model based on ANSYS and ZEMAX is briefed in the first from an overview of point.
Afterwards, we discuss the establishment of thermal model. Complete power series polynomial with spatial coordinates
is introduced to present temperature field analytically. We also borrow linear interpolation technique derived from shape
function in finite element theory to interface the thermal model and structural model and further to apply the
temperatures onto structural model nodes. Thereby, the thermal loads are transferred with as high fidelity as possible.
Data interface and communication between the two softwares are discussed mainly on mirror surfaces and hence on the
optical figure representation and transformation. We compare and comment the two different methods, Zernike
polynomials and power series expansion, for representing and transforming deformed optical surface to ZEMAX.
Additionally, these methods applied to surface with non-circular aperture are discussed. At the end, an optical telescope
with parabolic primary mirror of 900 mm in diameter is analyzed to illustrate the above discussion. Finite Element
Model with most interested parts of the telescope is generated in ANSYS with necessary structural simplification and
equivalence. Thermal analysis is performed and the resulted positions and figures of the optics are to be retrieved and
transferred to ZEMAX, and thus final image quality is evaluated with thermal disturbance.
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