1 February 1992 Secondary mirror chopping system for large infrared telescope
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Abstract
A rapid back-and-forth motion of a secondary mirror is required for enhancement of weak signal-to-noise ratio by chopping the incoming beam to an infrared telescope. For a very large infrared telescope with a large secondary mirror (diameter of 500 mm, mass of 7 kg), a unique secondary mirror chopping system which is very light and suppresses mechanical vibration of a telescope during chopping motion is developed. The system has an active damper which cancels large reaction force to restrain excitement of the telescope. The damper is very compact and light, because a linear motor of the damper uses the same magnetic circuit as for a motor driving the mirror. The controller for moving the mirror and the damper consists of feedback and feedforward parts. A unique position command of the feedforward part accomplishes short transition time of the chopping motion without exciting resonances of the chopping mechanism. The system achieves a total mass of 100 kg, secondary mirror maximum chopping amplitude of 1.21 mrad, secondary mirror positioning accuracy of 4 microrad, and transition time of less than 10 msec without remaining vibration.
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Tetsu Yamamoto, Tetsu Yamamoto, Takaharu Ueda, Takaharu Ueda, Daisuke Ogata, Daisuke Ogata, Shigeki Mizuno, Shigeki Mizuno, } "Secondary mirror chopping system for large infrared telescope", Proc. SPIE 1619, Vibration Control in Microelectronics, Optics, and Metrology, (1 February 1992); doi: 10.1117/12.56822; https://doi.org/10.1117/12.56822
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