DOI QR코드

DOI QR Code

Design of 3-Axis Focus Mechanism Using Piezoelectric Actuators for a Small Satellite Camera

소형 위성 카메라의 압전작동기 타입 3-축 포커스 메커니즘 설계

  • Hong, Dae Gi (Dept. of Aerospace and Mechanical Engineering, Graduate School at Korea Aerospace University) ;
  • Hwang, Jai Hyuk (Dept. of Aerospace and Mechanical Engineering, Korea Aerospace University)
  • 홍대기 (한국항공대학교 항공우주 및 기계공학과) ;
  • 황재혁 (한국항공대학교 항공우주 및 기계공학부)
  • Received : 2018.02.05
  • Accepted : 2018.05.23
  • Published : 2018.06.30

Abstract

For Earth observation, a small satellite camera has relatively weak structural stability compared to medium-sized satellite, resulting in misalignment of optical components due to severe launching and space environments. These alignment errors can deteriorate the optical performance of satellite cameras. In this study, we proposed a 3-axis focus mechanism to compensate misalignment in a small satellite camera. This mechanism consists of three piezo-electric actuators to perform x-axis and y-axis tilt with de-space compensation. Design requirements for the focus mechanism were derived from the design of the Schmidt-Cassegrain target optical system. To compensate the misalignment of the secondary mirror (M2), the focus mechanism was installed just behind the M2 to control the 3-axis movement of M2. In this case, flexure design with Box-Behnken test plan was used to minimize optical degradation due to wave front error. The wave front error was analyzed using ANSYS. The fabricated focus mechanism demonstrated excellent servo performance in experiments with PID servo control.

지구 관측용 소형 위성카메라의 경우, 중대형 위성에 비해 상대적으로 약한 구조 안정성으로 인해 열악한 발사환경 및 우주환경에서 광부품의 정렬오차가 발생하기 쉽다. 발생한 정렬오차는 위성카메라의 광학 성능 저하를 유발시킨다. 본 연구에서는 소형 위성 카메라의 정렬오차를 보상하기 위하여 3축 포커스 메커니즘을 제안하였다. 이 메커니즘은 3개의 압전 작동기로 구성되어 x-축, y-축 틸트 및 디스페이스(De-space) 보정을 수행할 수 있다. 포커스 메커니즘의 설계 요구조건은 슈미트-카세그레인(Schmidt-Cassegrain) 타입의 목표 광학계 설계에서 도출되었다. 부경 정렬오차 보상을 위하여 부 반사경의 뒤에 포커스 메커니즘을 부착하여 부경의 3축 운동을 제어하였다. 이 때 파면오차로 인한 광학 성능 저하를 최소화하기 위한 플렉셔를 Box-Behnken 실험계획법을 통하여 설계하였으며, ANSYS를 이용하여 파면오차 해석을 수행하였다. 제작된 포커스 메커니즘은 작동기의 수학적 모델링, PID 제어기 설계, 서보 제어실험을 통해 서보성능을 검증하였다.

Keywords

References

  1. Herbert J. Kramer, Arthur P. Cracknell, "An Overview of Small Satellites in Remote Sensing," International Journal of Remote Sensing, Vol. 29, No. 15, pp. 4285-4337, 2008. https://doi.org/10.1080/01431160801914952
  2. Braam Ben, H. A. van Mierlo, G. Buvril, S. Gill, "Meteosat Second Generation Refocusing Mechanism," ESA - SP(European Space Agency - Special Publication), Vol. 410, pp. 27-34, 1997.
  3. J. S. Chang, J. U. Kim, M. S. Kang, S. U. Yang and E. E. Kim, "Development and Verification of Thermal Control Subsystem for High Resolution Electro-Optical Camera System, EOS-D Ver.1.0," Journal of The Korean Society for Aeronautical and Space Sciences, Vol. 41, No. 11, pp. 921-930, 2013. https://doi.org/10.5139/JKSAS.2013.41.11.921
  4. D. H. Lee, D. C. Seo, J. H. Song, J. H. Chung, S. Y. Park, M. J. Choi and H. S. Lim, "Image Restoration of Calibration and Validation for KOMPSAT-2," International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 37, No. B1, pp. 57-62, 2008.
  5. Leger D., Viallefont F., Hillairef E. and Meygret A., "In-flight refocusing and MTF assessment of SPOT5 HRG and HRS cameras," Progress in Biomedical Optics and Imaging (SPIE Proceedings Series), No. 4881, pp. 224-231, 1999.
  6. Viallefont-Robinet, Francoise, "Edge method for on-orbit defocus assessment," Optics Express, Vol. 18, No. 20, pp. 20845-20851, 2010. https://doi.org/10.1364/OE.18.020845
  7. H. J. Kim, Y. D. Seo, S. K. Youn, S. H. Lee, D. G. Lee, E. S. Lee, "Optimal Design of the Flexure Mounts for Satellite Camera by Using Design of Experiments," Transactions of The Korean Society of Mechanical Engineers A., Vol. 32, No. 8, pp. 693-700, 2008. https://doi.org/10.3795/KSME-A.2008.32.8.693
  8. D. H. Lee and J. H. Hwang, "An Online Tilt Estimation and Compensation Algorithm for a Small Satellite Camera," Proceedings of The Asia-Pacific International Symposium on Aerospace Technology, pp. 1572-1582, 2017.
  9. J. B. Jo, J. H. Hwang and J. S. Bae, "Optical Design for Satellite Camera with Online Optical Compensation Movements," Journal of The Korean Society for Aeronautical and Space Sciences, Vol. 43, No. 3, pp. 265-271, 2015. https://doi.org/10.5139/JKSAS.2015.43.3.265
  10. M. S. Kang, "Study on the design and control of the focal plane compensation device for image stabilization of high-resolution small satellite," Unpublished master's thesis, School of Aerospace and Mechanical Engineering, Korea Aerospace University, 2016.