Dr. Laleh Makarem Profile

Dr. Laleh Makarem

at Ecole Polytechnique Fédérale de Lausanne

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Publications (5)

Proceedings Article | 10 July 2018 Paper

Priority coordination of fiber positioners in multi-objects spectrographs

Dominique Tao, Laleh Makarem, Mohamed Bouri, Jean-Paul Kneib, Denis Gillet

Proceedings Volume 10702, 107028K (2018) https://doi.org/10.1117/12.2313962

KEYWORDS: Spectrographs, Logic, Optical fibers, Spectroscopes, Algorithm development, Collision avoidance

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Projects such as "The Dark Energy Spectroscopic Instrument” (DESI) [4] or ”The Multi Object Optical and Near-infrared Spectrograph” (MOONS ) [5] are developing spectrographs, composed of more than thousand of optical fibers in a confined hexagonal focal plane, to study the evolution of the universe. Such systems allow fast reconfiguration of the fibers as they are moved simultaneously to their assigned target by a 2-arm positioner within an short interval of time. Moreover, astronomers prioritize the observation of some objects over those that hold less information, creating a hierarchy of importances or priorities. In a scenario where not all the positioners can reach their targets, It is important to ensure the observation of the high-priority targets. In previous works, a decentralized navigation function from the family of potential fields was used for collisionfree coordination. While it guarantees convergence of all the positioners to their targets for DESI [1,2], it fails at planning motion for positioners in MOONS [3]. The reason is that the second arm of the positioners in MOONS is two times the length of the first arm. Covering a larger working space, they are prone to deadlocks, a situation where two or more positioners are blocked by each other and so unable to reach their targets. In this paper and in the framework of MOONS project, we present our new approach to integrate assigned priorities with the decentralized navigation functions to reduce the deadlocks situations. For this purpose, we regulate the movements of the positioners using a finite-state machine combined with distance-based heuristics. Each positioner’s state dictates its behaviors with respect to other positioners. Distance-based heuristics limit the states transition when a positioner is interacting with its adjacent positioners to localize possible deadlock situations. The advantage of this method is its simplicity as it relies on local interaction of positioners, keeping the complexity of the algorithm quasilinear. In addition, since it does not depend on the positioner’s geometry, it is also scalable to other positioner kinematics. We developed a motion planning simulator with a graphic interface in python to validate the coordination of the positioners with assigned priorities. As a result, the number of positioners converging to their targets improve from 60-70% to 80-95%. The computation time of the trajectories increases slightly due to the new layer of algorithm added for deadlocks prevention.

Proceedings Article | 26 July 2016 Paper

Target-based fiber assignment for large survey spectrographs

Christoph Schaefer, Laleh Makarem, Jean-Paul Kneib

Proceedings Volume 9913, 991335 (2016) https://doi.org/10.1117/12.2232428

KEYWORDS: Detection and tracking algorithms, Spectroscopy, Spectrographs, Optimization (mathematics), Target acquisition, Nomenclature, Metrology, Telescopes, Astronomy, Current controlled current source

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Proceedings Article | 26 July 2016 Paper

Collision-free coordination of fiber positioners in multi-object spectrographs

Laleh Makarem, Jean-Paul Kneib, Denis Gillet

Proceedings Volume 9913, 99130V (2016) https://doi.org/10.1117/12.2231716

KEYWORDS: Actuators, Astronomical imaging, Spectrographs, Collision avoidance, Detection and tracking algorithms, Spectroscopy, Prototyping, Electronics, Robots, Kinematics

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Many fiber-fed spectroscopic survey projects, such as DESI, PFS and MOONS, will use thousands of fiber positioners packed at a focal plane. To maximize observation time, the positioners need to move simultaneously and reach their targets swiftly. We have previously presented a motion planning method based on a decentralized navigation function for the collision-free coordination of the fiber positioners in DESI. In MOONS, the end effector of each positioner handling the fiber can reach the centre of its neighbours. There is therefore a risk of collision with up to 18 surrounding positioners in the chosen dense hexagonal configuration. Moreover, the length of the second arm of the positioner is almost twice the length of the first one. As a result, the geometry of the potential collision zone between two positioners is not limited to the extremity of their end-effector, but surrounds the second arm. In this paper, we modify the navigation function to take into account the larger collision zone resulting from the extended geometrical shape of the positioners. The proposed navigation function takes into account the configuration of the positioners as well as the constraints on the actuators, such as their maximal velocity and their mechanical clearance. Considering the fact that all the positioners' bases are fixed to the focal plane, collisions can occur locally and the risk of collision is limited to the 18 surrounding positioners. The decentralizing motion planning and trajectory generation takes advantage of this limited number of positioners and the locality of collisions, hence significantly reduces the complexity of the algorithm to a linear order. The linear complexity ensures short computation time. In addition, the time needed to move all the positioners to their targets is independent of the number of positioners. These two key advantages of the chosen decentralization approach turn this method to a promising solution for the collision-free motion-planning problem in the next- generation spectroscopic survey projects. A motion planning simulator, exploited as a software prototype, has been developed in Python. The pre-computed collision-free trajectories of the actuators of all the positioners are fed directly from the simulator to the electronics controlling the motors. A successful demonstration of the effectiveness of these trajectories on the real positioners as well as their simulated counterparts are put side by side in the following online video sequence (https://goo.gl/YuwwsE).

Proceedings Article | 18 July 2014 Paper

Collision-free motion planning for fiber positioner robots: discretization of velocity profiles

Laleh Makarem, Jean-Paul Kneib, Denis Gillet, Hannes Bleuler, Mohamed Bouri, Philippe Hörler, Laurent Jenni, Francisco Prada, Justo Sánchez

Proceedings Volume 9152, 91520Q (2014) https://doi.org/10.1117/12.2055185

KEYWORDS: Robots, Collision avoidance, Safety, Spectroscopy, Spectrographs, Galactic astronomy, Baryon acoustic oscillations, Kinematics, Robotic systems, Computer simulations

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Proceedings Article | 8 July 2014 Paper

Developing micro DC-brushless motor driver and position control for fiber positioners

Laurent Jenni, Philipp Hörler, Laleh Makarem, Jean-Paul Kneib, Denis Gillet, Hannes Bleuler, Mohamed Bouri, Francisco Prada, Guillermo De Rivera, Justo Sanchez

Proceedings Volume 9147, 914744 (2014) https://doi.org/10.1117/12.2055197

KEYWORDS: Robots, Actuators, Microcontrollers, Telescopes, Control systems, Sensors, Robotics, Space telescopes, Bridges, Molecular bridges

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