Tertiary mirror of thirty meter telescope (TMT) has the tracking and pointing capabilities, and its structure is similar to an alt-az telescope. The cradle serves a similar function to the center block of the track frame, its structure directly affects the performance of the system. M3 prototype as an example, in order to improve stiffness to weight ratio of the cradle, the mathematical model of topology optimization design of the cradle was established and the optimization was performed. Then a spliced truss structure for cradle was designed based on the result of the topology optimization. By using finite element method, the static and dynamic analysis of cradle under different conditions was done according to the working characteristics. The results showed that under the conditions of the gravity vertical along the x, y, z, the maximum deformation of cradle was 0.064mm, 0.015mm, 0.025mm respectively, and the first modal frequency is 74.4Hz. Results showed the structure designed meets the requirement.
The Thirty Meter Telescope (TMT) is one of the largest ground-based telescopes currently under construction in the world. Changchun Institute of Optics, Fine Mechanics and Physics(CIOMP) took the task of design and manufacture Tertiary Mirror System (M3S), which is also named Giant Steerable Science Mirror(GSSM). CIOMP decided to design and manufacture a 1/4 scaled prototype of M3S(M3SP) to verify the technical feasibility of M3S design. The tertiary mirror was support by 18 points whiffletree structure along axial direction and 12 points whiffletree structure along lateral direction. Finite Element Model was built to evaluate the system performance. Based on the Finite Element Analysis, the SlopeRMS of tertiary mirror surface figure would be 1.9 μrad when the mirror was pointed vertical under gravity, and was 0.46μrad when the mirror was pointed horizontally. By applying adjust moment on the pivot of axial whiffletree system, the surface figure SlopeRMS when mirror was pointed vertically could be improve to 0.95μrad. The support system’s resonance frequency was 53.7Hz, which indicated that the system stiffness was high enough. Mirror and structure stress level and meet the requirement of system safety.
The Thirty Meter Telescope (TMT) project will design and build a thirty-meter diameter telescope for research in astronomy in visible and infrared wavelengths. The primary mirror of TMT is made up of 492 hexagonal mirror segments under active control. The highly segmented primary mirror will utilize edge sensors to align and stabilize the relative piston, tip, and tilt degrees of segments. The Support System Assembly (SSA) of segmented mirror utilizes a Guide Flexure to decouple the axial support and lateral support while its deformation will bring in measurement error of edge sensor. We have analyzed the theoretical relationship between the segment movement and the measurement value of edge sensor and proposed an error correction method with matrix. The correction process and the simulation results of the edge sensor will be described in this paper.
Warping Harness is a mechanism which can periodically correct the low order surface errors of mirror. The main correction objects are the residual error of the mirror machining, the stress distortion caused by the coating, the surface error caused by the temperature load, even with the errors caused by the gravity change, and so on. In principle, the zero moment point of the Whiffletree structure can be adjusted by changing the deflection of the warping harness blade. Due to the closed force system, once the moment induced by the warping harness changes, the load distribution on the whiffletree structure varies too. In practice, the structure of Warping Harness is installed on each group of Whiffletree joints and works with the structure of Whiffletree. The servo stepping motor is employed to control the bending of the spring blade to change the distribution of the support force, and then the correction of the main mirror surface figure is completed. This paper mainly introduces the correction principle of Warping harness and its principle, and demonstrates the preliminary design of the system.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT). This paper will combine PSSn to analyze the error characteristics of GSSM. To evaluate the performance of the large telescope under different kinds of error source, the normalized point source sensitivity is introduced, which is firstly studied by the group of thirty meter telescope team to balance all the deviation of the telescope and also budget the error. First and foremost, the character of the normalized point source sensitivity is studied in the very first part and the advantage in the evaluation in all the frequency domain. Then the PSSn is compared with the traditional metric, such as RMS and the multiplication property is discussed. The experienced formula is used to show the relationship between the PSSn and the error sources, static and dynamic. Lastly, the method is applied to a large aperture telescope.
Large telescopes are developing, and promoted by new technological developments. In order to study the method of mirror seeing detection for large aperture optical system, the relationship between mirror seeing and slope information is derived first. In order to evaluate the results more comprehensively, the normalized point source sensitivity was introduced to evaluate the results. Finally, according to the previous analysis, the experiment was carried out. The change normalized point source sensitivity under different conditions is calculated. By comparing with RMS of wavefront, the better statistical characteristic of sensitivity of normalized point source was verified.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which has got into the preliminary design phase in 2017. To develop the passive support structure system for the largest elliptic-plane flat mirror and a smoothest tracking mechanism for the gravity-variant condition, CIOMP had developed a 1/4 scale, functionally accurate version of the GSSM prototype as the pre-construction of GSSM. The prototype incorporates the same optical-mechanical system and servo control system as GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5 mm with elliptic-plane figure and is supported by 18 points whiffletree on axial and 12 points whiffletree on lateral. The main objective of the preconstruction includes validate the conceptual design of GSSM and increase more confidence when meet the challenge during the development of GSSM. The assembling, integration and verification of the prototype have been completed based on the test results. CIOMP has got the sufficient test results during the pre-construction phase and got into the preliminary design for GSSM.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will enter the preliminary design phase in 2016. The GSSM is the tertiary mirror of TMT and consists of the world’s largest flat telescope mirror (approximately 3.4m X 2.4 m X 100mm thick) having an elliptical perimeter positioned with an extremely smooth tracking and pointing mechanism in a gravity-varying environment. In order to prepare for developing this unique mirror system, CIOMP has been developing a 1/4 scale, functionally accurate version of the GSSM prototype during the pre-construction phase of GSSM. The prototype will incorporate the same optomechanical system and servo control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with an elliptical perimeter. The mirror will be supported axially by an 18 point whiffletree and laterally with a 12 point whiffletree. The main objective of the preconstruction phase includes requirement validation and risk reduction for GSSM and to increase confidence that the challenge of developing the GSSM can be met. The precision mechanism system and the optical mirror polishing and testing have made good progress. CIOMP has completed polishing the mirror, the prototype mechanism is nearly assembled, some testing has been performed, and additional testing is being planned and prepared. A dummy mirror is being integrated into the cell assembly prototype to verify the design, analysis and interface and will be used when testing the prototype positioner tilt and rotation motions. The prototype positioner tilt and rotator structures have been assembled and tested to measure each subsystem’s jitter and dynamic motion. The mirror prototype has been polished and tested to verify the polishing specification requirement and the mirror manufacturing process. The complete assembly, integration and verification of the prototype will be soon finished. Final testing will verify the prototype requirements including mounted mirror surface figure accuracy in 5 different orientations; rotation and tilt motion calibration and pointing precision; motion jitter; and internally generated vibrations. CIOMP has scheduled to complete the prototype by the end of July 2016. CIOMP will get the sufficient test results during the pre-construction phase to prepare to enter the preliminary design for GSSM.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will get into the preliminary design phase in 2016. To develop the passive support structure system for the largest elliptic-plan flat mirror and smoothest tracking mechanism for the gravity-invariant condition, CIOMP is designing and building a 1/4 scale, functionally accurate version of the GSSM prototype. The prototype will incorporate the same optical-mechanical system and electric control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with elliptic-plan figure and will be supported by 18 points whiffletree on axial and 12 points whiffletree on lateral. The mirror surface figure will be evaluated by SlopeRMS which is the final evaluation method used in the actual GSSM. The prototype allows the mirror point to and be tested in five specified gravity orientations and meet the requirements of SlopeRMS. The prototype testing platform will have the interfaces with direct drive systems. The jitter testing will be implemented on the prototype system to verify the bearing, the encoder, the servo control algorithm in the low speed up to 5 arcsecond per second. The total prototype system configured mirror surface figure will be better than 1 micro radian SlopeRMS in each tested orientation. The positioner jitter will be less than 0.1 arcsecond RMS for tilt and rotator axis respectively and will be analyzed with frequency domain to meet the requirements of the TMT adaptive optics system. The pre-construction will be completed at the beginning of 2016 and provide the technical support to the preliminary design of GSSM.
BaTiO3 film is deposited on single crystal MgO substrate with pulsed laser deposition, and its crystal structure and surface roughness are characterized by X-ray diffraction instrument and atomic force microscope. BaTiO3 film crystal quality is analyzed under three different oxygen partial pressure and three different annealing temperatures. The result shows that when the oxygen partial pressure is 15Pa, crystal surface (001) and (002) diffraction peak of BaTiO3 thin films have higher intensity. It indicated that the film has a good c-axis orientation. When the annealing temperature is 800°C, the intensity of diffraction peak is the maximum, and peak shape is sharper. BaTiO3 crystal film is obtained with highly preferred orientation, and film density is improved. Thus the film has less surface roughness and good crystalline state.
For large aperture telescope, we place the significance on the jitter of the wave front parameters when we make
effort to obtain better image. We investigate the power spectral density for charactering the optical jitter for large
telescope as stochastic sequence. Limited by frequency domian property, the universal used metric, and root mean square
of wave front error (RMS WFE) cannot provide adequate information .This paper provides a complete and easy-to-use
approach to the specification of mid-and-high frequency aberration of the wave front. Additionally, we apply welch
method to the calculation of the power spectral density to achieve the accuracy result without much noise involved.
Lastly, we verify this theory by the analysis of a laser system.
We investigate a new metric power spectral density (PSD),for characterizing the performance of seeing-limited large telescope such as thirty meter telescope(TMT ). As the PSD is directly related to the performance of the atmosphere which plays an important role in ground based facilities, it represents the efficiency lose due to mid and high-spatial frequency components in observing time. The metric also properly counts for the optic error of the mirror itself such as the deviations from a perfect surface, and metrology measurement errors .The metric can multiply all the errors which differentiates from the traditional ones, such as RMS. We also numerically confirm this feature for Karman model atmosphere error multiplied with the sample of our vendor and the TMT M3.Additonaly, we discuss other pertinent feature of the PSD, including its relationship to Zernike aberration ,and RMS of wave front errors.
TMT Tertiary Mirror System (M3S) is required to be able to track and point. It should rotate with the observing object. In this article, the schemes of Tertiary Mirror supporting assembly and position assembly are introduced. Then, the static and dynamic performance of Tertiary Mirror System has been analyzed. It is shown that, the maximum deflection is 1.024 mm, the maximum stress is 138.91MPa when gravity is affecting. The security of M3S can be assured when telescope is working at all required positions. The first nature frequency is 15.39Hz, the requirement 15 Hz has been satisfied. In addition, the response to earthquake has been estimated primarily. Results shows that when earthquake with mean return time 200 year happens in three directions simultaneous, or earthquake with mean return time 1000 years happens, the lateral support will be destroyed. Protection measures should be considered. Conclusions in this article are useful guides for the M3S design.
In order to analyze the tracking performance and design the controllers for TMT-M3 control system in the design stage. This paper presents the development of the analytical model of the gear driven large telescope using the lumped mass modeling method. The analytical model includes the telescope structure, its drives, the velocity loop and position loop. First, the modal model of a flexible structure is analyzed based on the finite-element data. And the modal model is transferred into the state-space model, in continuous-time. Next, the drive model is derived, and combined into the velocity loop and position loop. Finally, the impact of the error sources on the control loop properties is simulated. According to the simulation accuracy of the analytical modeling, the analytical model can be used in implementation, such as the model-based controllers.
The tertiary mirror positioned assembly (M3PA) of the thirty meters telescope (TMT) is the largest tertiary mirror pointing system in the world. The tracking and pointing performance of M3PA is better than any other telescopes which have been built, and the working condition is even worse, so the designers face an enormous challenge. The tracking system includes the bottom rotator shaft and the tilt shaft. The study of this paper focuses on the tilt shaft. There are mainly three forms. The first form is one end fixed with the other unrestrained in axial direction. The second form uses two pairs of angular contact ball bearing. The last form lays two tape roller bearings. All of them can meet the requirements when the M3PA is vertical. But the first one becomes invalid when the M3PA is horizontal. We pay our attention on the study for the second arrangement method.. This bearing arrangement can produce a good stiffness, and increase the first modal frequency to 15.1Hz. In addition, some analysis were down to study the load applied on the balls. The results show that the maximum load is up to 5000N with the stress of 2300MPa.
During the alt-azimuth telescope tracking, due to the frame structure of tracking support and relative movement of each mirror in Coude optical path, image plane is rotating. To eliminate the effects of image rotation for imaging and subsequent image processing, dove prism or K mirror are generally used. A set of K mirror system designed for 2m telescope. Affected by various errors in the alignment process, the rotating axis K, the optical axis of the K mirror, and the optical axis of the telescope’s optical system can’t be fully coincide. This causes the track optical axis drawn on the image is not a point, but a Pascal’s limacon. The impact caused by the various sources of error were analyzed in this paper and simulation results have important guiding significance for the alignment error distribution.
In order to evaluate and test the image quality of large aperture telescope, the most directly method is adopting the collimator and test the telescope system with full aperture. Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) commenced developing the large aperture collimator for interferometric and image quality testing of meter scale optical systems under cryogenic, vacuum conditions. The aperture of the collimator which has been on the conceptual design phase is 1.5m diameter, and the optical configuration is Cassegrain, the focus is 50m. The material of reaction bonded Silicon Carbide (RB-SiC) produced by CIOMP will be used as the primary mirror substrate. And the figure accuracy of the primary mirror will be polished better than 15nm (RMS). The collimator will be working in a vacuum chamber and face down vertically to the unit under test. The application requirements, specification requirements, and some key technology are demonstrated and analysed with finite element analysis (FEA) in the paper. The feasibility, error budget, and hazards evaluation of the collimator are fulfilled by the FEA results. It demonstrated that the conceptual design meet the requirements of the 1.5m aperture vertical collimator, and could achieve the high accuracy requirements of the wavefront for the beam of light in the vacuum chamber, which the wavefront error should less than 32nm(RMS). Mechanical alignment errors induced by thermal and structural perturbations are monitored with an auto-focusing system to enable focus compensation. The ambient temperature of the collimator in chamber are controlled allowing testing while the chamber shrouds and test unit are brought to cryogenic temperatures. With the high accuracy of the wavefront, the collimator could test the image resolution, modulation transfer functions (MTFs), point spread functions (PSFs), encircled energy, wavefront error, best focus, etc. for optical systems. And the conceptual design could be consulted to other large aperture collimators.
With the development of infrared technology and material, infrared zoom system is playing an important role in the field of photoelectric observation, the demand of infrared systems is increasing rapidly. In order to satisfy the requirement of infrared tracking imaging requirements of a car optoelectronic devices, different kinds of mechanical structure has been discussed, finally, according to the character of the optical design result, cam mechanism is adopted in zoom mechanism design, ball screw has been used in focusing mechanism design. As is known to all, cam is the key part in zoom system, the static, dynamic and thermal characteristics of the cam make great effect on the system performance because of the greater impact of the car’s shaking and a larger range of temperature changes, as a result, the FEM analysis is necessary. The static performance is all right obtained by the finite element analysis results, the cam’s first -order natural frequency is 97.56 Hz by modal analysis, the deformation of cam in the temperature difference of 80 °C is no more than 0. 003 mm by thermal analysis, which means the mechanical performance of the cam is fine. at last, the focusing mechanism has been designed, and analysis of focusing mechanism precision and encoder theoretical resolving power has been done, this mechanism has the advantages of simple transmission chain and low friction, as well as reducing the transmission error, an absolute encoder is chosen to detect the displacement of the focusing mechanism, the focusing precision is 5μm, the encoder theoretical resolving power is 0.015μm. In addition, the measurements on how to suppress stray radiation have been put forward. The experiment afterward showed that the infrared zoom system performs well, which provides lot of experience in infrared zoom system design and adjustment.