An easily scalable Theta/Phi fiber positioner to reduce risks, lead times, and costs for multi-object spectrographs

Kronig, Luzius; Caseiro, Stefane; Hug, Markus; Charif, Majid; Bouri, Mohamed; Kneib, Jean-Paul

doi:10.1117/12.2562717

Cited by 1 publication

(1 citation statement)

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“…Theta-phi positioners were first designed and adopted by the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST; Xing et al 1998). They have been widely adopted by the Super Ifu Deployable Experiment (SIDE; Prada et al 2008;Azzaro et al 2010), LAMOST second stage (Hu et al 2016(Hu et al , 2018Guo et al 2022), Multi-Object Optical and Nearinfrared Spectrograph (MOONS;Horler et al 2018;Kronig et al 2020a;Gonzalez et al 2022), Prime Focus Spectrograph (PFS; Fisher et al 2014;Wang et al 2022), and Dark Energy Spectroscopic Instrument (DESI;Fahim et al 2015;Martini et al 2018;Silber et al 2023). R-theta positioners have been designed for SIDE (Schlegel & Ghiorso 2008), BigBOSS (Silber et al 2012), 4MOST (Saviauk et al 2014), and VLT-MOONS and VLT-KMOS (Louth et al 2022).…”

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confidence: 99%

The Calibration of theta-phi Fiber Positioners Based on the Differential Evolution Algorithm

Zhang,

Huang,

Chen

et al. 2024

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Robotic fiber positioner (RFP) arrays are commonly adopted in multiobject spectroscopic instruments. The positioning accuracy is a common but vital issue for RFP as inaccurate fiber placement may heavily affect the observation performance. The calibration of RFP can effectively improve the positioning accuracy. Least-square is a widely used calibration method. However, it has disadvantages, such as sensitivity to the initial values and calculation complexity. To improve the positioning accuracy and reduce the iteration moves, we propose a new calibration method based on the differential evolution algorithm and verify it by calibrating the RFP of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope. We first build the kinematic models of the RFP based on the Denavit–Hartenberg matrix and geometry relationship. Then, we analyze the error components and present the proposed calibration algorithms. The experiments are done with the digital universal tool microscope 19JC and the errors are calculated using the distance between the positions of achieved and target. Results show that the proposed algorithm can achieve higher accuracy than the least-square method and the average positioning accuracy is improved by 78.94% after calibration. Combined with the “pulse reduction” strategy and close-loop compensation, after two moves, the positioners can place the fiber ends within 40 μm of the intended location. The proposed calibration method is also suitable for other similar theta-phi positioners.

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