Parallel robots in a ground-based telescope active optics system: theory and experiments

Schipani, P.; Ferragina, L.; Marty, Laurent; Grado, A.; Fiore, L. Di; Rosa, R. De; Rana, Abhilasha; Busatta, A.

doi:10.1117/12.754172

Cited by 3 publications

(2 citation statements)

References 17 publications

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“…Therefore, the parallel mechanism with high load capacity is the most suitable choice. The parallel mechanism has been widely used in active optical focusing systems, such as Gran Telescopio Canarias (Casalta et al 2004), VLT Survey Telescope (Schipani et al 2007(Schipani et al , 2008, and James Webb Space Telescope (Wells et al 2004;Chonis et al 2018). It is worth noting that the effect of varying temperatures on optical imaging quality cannot be ignored.…”

Section: Introductionmentioning

confidence: 99%

Design and Cryogenic Performance of a Hexapod Platform for a Large Ground-based Wide Field Survey Telescope

Yu,

Wang,

Zhang

et al. 2023

Res. Astron. Astrophys.

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Thermal gradient is an important factor causing degradation in the image quality of telescopes. In order to ensure the accurate alignment of the primary focus unit and the primary mirror, the hexapod platform (as a corrector) is investigated in this paper. First, a ground-based telescope with 2.5 m aperture and 3.5 deg field of view is described. The telescope is under construction, and it is expected to be finished in 2023. Secondly, the hexapod platform with flexure hinges utilized to adjust the primary focus unit is proposed, which is applied as a corrector. Then, the inverse kinematics of the platform is established and an open-loop control system is built based on it. Finally, the cryogenic performance test for the hexapod platform is performed. The experimental results show that the resolution and repeatability of the translation for the hexapod platform can be achieved at the micro-meter level. The resolution and repeatability of the rotation can be achieved at the arc-second level. Therefore, the cryogenic performance of the hexapod platform can meet the optical imaging requirements of the wide-field ground-based telescope. The kinematic analysis and cryogenic performance tests in the paper provide a technical reference for the precise alignment of the primary focus unit and the primary mirror, which can improve the imaging quality of the telescope.

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Section: Introductionmentioning

confidence: 99%

Design and Cryogenic Performance of a Hexapod Platform for a Large Ground-based Wide Field Survey Telescope

Yu,

Wang,

Zhang

et al. 2023

Res. Astron. Astrophys.

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“…The relative position of the primary and secondary mirrors predominantly depends on adjusting the secondary mirror's pose. The secondary mirror's positioning capability allows the correction of defocus and coma optical aberrations, which are usually caused by incorrect relative positions of the optics [1].…”

Section: Introductionmentioning

confidence: 99%

ADRC control of a 6-DOF parallel manipulator for telescope secondary mirror

Ye¹,

Zhi²,

Gu³

2017

J. Inst.

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In view of the special requirements of the secondary mirror control system on large aperture telescopes, an improved 6-DOF parallel manipulator is designed and used to replace the traditional hexapod used in telescope secondary mirror position dynamic compensation. A highly robust active disturbance rejection controller (ADRC) is designed, which consists of a nonlinear tracking differentiator (NTD), an extended state observer (ESO), a nonlinear state error feedback law (NLSEF), and disturbance compensation. The ESO can track the all-order state variables, as well as estimate and compensate for unmodeled dynamics and total external disturbance of the system. The results of simulation indicate that the ADRC can improve tracking precision and control performance when it is compared with the proportion integration differentiation (PID) controller. The test results show that the absolute accuracy of the three dimensional parallel motions is about ±4 µm, and the two dimensional tilts' is about 10 µrad. The control precision meets the system design for a telescope secondary mirror.

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