The DESI fiber positioner system

Schubnell, M.; Ameel, Jon; Besuner, Robert; Gershkovich, Irena; Heetderks, H.; Hoerler, P.; Kneib, Jean-Paul; Silber, Joseph; Tarlè, G.; Weaverdyck, Curtis

doi:10.1117/12.2233370

Cited by 22 publications

(19 citation statements)

References 3 publications

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“…Each pointing of DESI, or tile, consists of a total of 5,000 fibres, arranged on the focal plane in 10 wedge-shaped 'petals' (Schubnell et al 2016). Each individual fibre is controlled by a robotic fibre positioner which can rotate on two arms, allowing the fibre to be placed on any object within a unique circular patrol region (see e.g.…”

Section: Robotic Fibre Positionersmentioning

confidence: 99%

Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey

Smith

Cole

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) will be a survey of bright, low redshift galaxies, which is planned to cover an area of ∼ 14, 000 sq deg in 3 passes. Each pass will cover the survey area with ∼ 2000 pointings, each of area ∼ 8 sq deg. The BGS is currently proposed to consist of a bright high priority sample to an r-band magnitude limit r ∼ 19.5, with a fainter low priority sample to r ∼ 20. The geometry of the DESI fibre positioners in the focal plane of the telescope affects the completeness of the survey, and has a non-trivial impact on clustering measurements. Using a BGS mock catalogue, we show that completeness due to fibre assignment primarily depends on the surface density of galaxies. Completeness is high (>95%) in low density regions, but very low (<10%) in the centre of massive clusters. We apply the pair inverse probability (PIP) weighting correction to clustering measurements from a BGS mock which has been through the fibre assignment algorithm. This method is only unbiased if it is possible to observe every galaxy pair. To facilitate this, we randomly promote a small fraction of the fainter sample to be high priority, and dither the set of tile positions by a small angle. We show that inverse pair weighting combined with angular upweighting provides an unbiased correction to galaxy clustering measurements for the complete 3 pass survey, and also after 1 pass, which is highly incomplete.

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Section: Robotic Fibre Positionersmentioning

confidence: 99%

Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey

Smith

Cole

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Therefore, no particular measure has to be considered to avoid the collisions. Others that have rigid parts 5,10 have to avoid the collision between adjacent positioners. Some solutions have reported that handling the movement speed would suffice for avoiding the collision.…”

Section: Architecture Requirementsmentioning

confidence: 99%

“…It has since benefited from a number of mechanical refinements that improve positioning performance, which is now being implemented in 4MOST. [6][7][8][9] DESI 10 is another example of this technology that will use 5000 robotically controlled fiber-positioners feeding 10 identical spectrographs. LAMOST 11 is an on-going project using 4000 positioning fibers connected to 16 spectrographs.…”

Section: Introductionmentioning

confidence: 99%

“…9, the use of CAN bus is mentioned as an example of standard communication because "its use removes the need for almost all ancillary electronics around the field and considerably reduces mass," but there is no comparison made to other communication systems, and the use of this protocol in the instrument is not clearly specified. Schubnell et al 10 and Lang-Bardl et al 16 present the use of CAN bus but provide no explanations (project 4MOST), either comparative or argumentative. Schubnell et al 10 only state that each positioner receives a synchronization signal to facilitate easy co-ordination of the motion of multiple positioners and that each one has a unique ID that can be physically placed anywhere on the bus.…”

Section: Introductionmentioning

confidence: 99%

“…Schubnell et al 10 and Lang-Bardl et al 16 present the use of CAN bus but provide no explanations (project 4MOST), either comparative or argumentative. Schubnell et al 10 only state that each positioner receives a synchronization signal to facilitate easy co-ordination of the motion of multiple positioners and that each one has a unique ID that can be physically placed anywhere on the bus. Li et al 17 propose a method of wire communication to control the fiber positioning nodes, which are driven by two stepping motors.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of communication architectures for a fiber-positioning spectrograph

Martínez-García

Lopez-Colino

Garrido

et al. 2019

J. Astron. Telesc. Instrum. Syst.

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The communication architecture required to provide a bidirectional communication between a central command node and a full set of fiber positioners feeding a spectrograph is studied. Six different architectures have been analyzed in terms of communication time and power consumption. These architectures are the result of the combination of three different communication protocols: transmission control protocol/internet protocol (TCP/IP) over ethernet, interintegrated circuit (I 2 C), and controller area network. The design of communication architecture must prioritize between communication time and power consumption. The fastest architecture is the hybrid TCP/IP over ethernet-I 2 C. This architecture requires the least time to provide a full set of coordinates to every fiber positioner less than 50 ms. The most power efficient solution is the I 2 C-I 2 C with demultiplexers. This architecture solves a bidirectional communication between a central node and a full set of fiber positioners requiring only an addition of 27 mW.

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