Associate for Education and Public Outreach
Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
- Degree
- Ph.D. in Engineering(Mar, 1991, The University of Tokyo)
- J-GLOBAL ID
- 201801002275500853
- researchmap Member ID
- B000340311
Papers
54-
Smart Materials and Structures, 30(6) 065014-065014, Jun 1, 2021Abstract We propose and demonstrate a novel method to enhance vibration harvesting based on surge-induced synchronized switch harvesting on inductor (S3HI). S3HI allows harvesting of a large amount of energy even from low-amplitude vibrations by inducing a surge voltage during the voltage inversion of a synchronized switch harvesting on inductor (SSHI). The surge voltage and the voltage amplification from the conventional voltage inversion improve energy harvesting. S3HI modifies SSHI by both rewiring the circuit without adding components and using a novel switching pattern for voltage inversion, thus maintaining the simplicity of SSHI. We propose a novel switching strategy and circuit topology and analyze six methods that constitute the S3HI family, which includes traditional S3HI and high-frequency S3HI. We demonstrate that the six methods suitably harvest energy even from low-amplitude vibrations. Nevertheless, the harvestable energy per vibration cycle depends on the switching pattern and storage-capacitor voltage. The use of the proposed switching strategy, which allows energy harvesting before energy-dissipative voltage inversion, substantially increases the harvestable energy per vibration cycle. In the typical case considered in this study, the said increase is on the order of 11%–31% and 15%–450% compared to the traditional and existing high-frequency S3HI methods, respectively, depending on the storage-capacitor voltage. Additionally, the proposed circuit can be used as a traditional circuit. It could be considered a promising alternative to S3HI methods owing to its potential auto-reboot capability, which is not found in traditional S3HI circuit.
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AIAA Scitech 2019 Forum, 2019Hitomi (ASTRO-H) was an X-ray astronomical satellite launched on Feb. 17, 2016. The Hitomi satellite had both two soft X-ray telescopes with a focal length of 5.6 m and two hard X-ray telescopes with a focal length of 12 m for observation with a wide energy range. In this paper, the structural performance of Hitomi satellite on orbit was reported. On Feb.28, 2016, a 6m Extensible Optical Bench (EOB) was successfully deployed. During the deployment, the induced vibration of EOB was observed. One of the major causes was estimated to be periodic constraint changes of the EOB’s root. After the deployment, the established stiffness and alignment performance of the EOB agreed well with the predicted values. Furthermore, high shape stability of the structure could be obtained on orbit.
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 16(2) 181-187, 2018<p>An Extensible Optical Bench (EOB) for a X-ray satellite (ASTRO-H) had a length of 6.4m in extended configuration. Although the same type of extensible mast was used in Space Radio Telescope (Halca) in 1997, the tip mass was quite different in the case of ASTRO-H. Due to the tip mass of 150 kg, the natural frequency of EOB was less than 1Hz in the extended configuration. ASTRO-H was launched on Feb. 17, 2016, and the EOB was extended on Feb. 28, 2016, successfully. However, because the vibration of EOB occurred during the extension, the extension operation was carried out over four passes intermittently. When the amplitude of induced vibration excessed the predefined threshold, we stopped the extension, then stayed until the vibration was damped. In this paper, the induced vibration during extension and its mechanism are reported. Through simulations, it is confirmed that one of the major causes of the vibration is a periodic change of gap between mast and canister at the root of EOB.</p>
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Journal of Astronomical Telescopes, Instruments, and Systems, 4(1), Jan 1, 2018 Peer-reviewed© The Authors 2018. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.
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JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 28(7) 888-906, Apr, 2017 Peer-reviewedThis article describes the optimal configuration and combination of piezoelectric transducers and inductors for the synchronized-switch-damping-on-an-inductor technique. The technique suppresses structural vibrations by inverting the polarity of the electric voltage in a piezoelectric transducer using a switched inductive shunt circuit at each displacement extremum. The energy dissipation rate of synchronized switch damping on an inductor depends on the impedances of the transducer and the inductor in the circuit, especially the resistive component, in this inversion. For this study, mathematical models of the equivalent resistances of transducers and inductors for this inversion phenomenon were formulated based on experiments with various transducers and inductors. Using these models, the optimal ratio of the thickness-area of patch-type piezoelectric transducers and that of the length-cross-sectional area of the lead of the inductors were analytically obtained. The optimization of series-parallel connections of multiple transducers and inductors was also shown to be equivalent to this one. The optimal mass budget allocation for the transducers and inductors was also formulated. Two examples of optimization, involving an increase in energy dissipation rates by a factor of 4, were presented. The examples showed that the time taken to suppress free vibrations in a clamped beam was reduced to half through the optimization.
Misc.
91-
観測ロケットシンポジウム2020 講演集 = Proceedings of Sounding Rocket Symposium 2020, Mar, 20213rd Sounding Rocket Symposium (March 24-25, 2021. Online Meeting)
Presentations
13-
33rd International Symposium on Space Technology and Science, Mar 1, 2022
Teaching Experience
2-
Oct, 2022 - Jan, 2023飛翔体構造工学概論 (東京大学大学院工学系研究科航空宇宙工学専攻)
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Aug, 2022 - Aug, 2022衛星システム設計学特論 (公立大学法人大阪)
Research Projects
12-
科学研究費助成事業, 日本学術振興会, Apr, 2023 - Mar, 2027
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科学研究費助成事業 基盤研究(C), 日本学術振興会, Apr, 2020 - Mar, 2023
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, Apr, 2014 - Mar, 2018
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, 2008 - 2010
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, 2007 - 2008
