Research and Development of Control Technology of Large Segmented Mirrors

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 17340053
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Astronomy
• Research Institution: Kyoto University
• Principal Investigator: IWAMURO Fumihide Kyoto Univ., Dept.of Astronomy, Associate Professor, 大学院理学研究科, 助教授 (80281088)
• Co-Investigator(Kenkyū-buntansha): NAGATA Tetsuya Kyoto Univ., Dept.of Astronomy, Professor, 大学院理学研究科, 教授 (80208016) ; OHTA Koji Kyoto Univ., Dept.of Astronomy, Associate Professor, 大学院理学研究科, 助教授 (50221825) ; YOSHIDA Michitoshi NAOJ, Okayama Astroph.Obs., Associate Professor, 光赤外研究部, 助教授 (90270446) ; OKITA Kiichi NAOJ, Okayama Astroph.Obs., Associate Professor, 光赤外研究部, 助教授 (60204096) ; IZUMIURA Hideyuki NAOJ, Okayama Astroph.Obs., Assistant, 光赤外研究部, 主任研究員 (00211730)
• Project Period (FY): 2005 – 2006
• Keywords: Optical and NIR Astronomy / Fine Polishing / Precise Measurement / Grinding / Accurate Position Control

Research Abstract

In the department of astronomy of Kyoto University, the 3.8m telescope project is now in progress using the technology required to construct the next-generation extremely large telescope. In this research project, we conducted the following studies as a part of this telescope project.
1. Designing and development of the mirror support system
We carried out the trial manufacture of a mechanical part to support the segmented mirror with the same bearing power. The support system does not yield any torque under any elevation angle of the telescope, placed in the narrow space behind the mirror. We found a few problem such as backlash and the mounting accuracy of a joint from this trial manufacture.
2. Development of actuator system to adjust the mirror support system
We improved and also carried out the trial manufacture of the actuator system, which adjust the above mirror support system with an accuracy of 〜10nm. The improved actuator can be placed just below the nodes of the truss structure , and is stably-operated even under a small load condition by the pressurized spring attached to the actuator axis driven with a harmonic-gear.
3. Test of the noncontact sensor for the accurate position measurement
The stability test of the noncontact inductance sensor for the relative position measurement among the segmented mirrors was continued. We found that the measured value is quite sensitive to bending the cables and also to the static of the facing plate. The new driving circuit of the sensor shows a small readout noise, but somewhat unstable in the long-term stability test. We will investigate the driving circuit having stability and low readout noise.
4. Development of basic technologies to measure the phase differences between the segmented mirrors
We designed the phase-difference measurement system using a spreading laser on the telescope focus and many half mirrors attached between the segmented mirrors. The basic principle was confirmed by the optical test in the laboratory. The next step is the demonstration of the fastest procedure to adjust the mirror position using the wavelength switching capability of the tunable laser.