Alexandre T. Lê

Alexandre T. Lê

he/him

French CIFRE PhD student in Mathematics & Robotics

Publications

You can also find my articles on my Google Scholar profile.

Certified kinematic tools for the design and control of parallel robots

Published in Mechanism and Machine Theory 2025, 2025

This paper presents a methodology for the design and control of Parallel Kinematic Robots (PKRs). First, one focuses on the problematics of design. In particular, given a parallel mechanism defined by its design parameters and its kinematic modeling as well as its prescribed workspace, the idea is to certify the absence of any numerical instabilities (computational and physical singularities) that may jeopardize the integrity of the robot. This is achieved through two complementary approaches: a global method using symbolic computation and a local one based on continuation techniques and interval calculus, accounting for uncertainties in the design. The methodology is then applied to real PKR examples. Secondly, the paper proposes a control strategy that limits the active joint velocities to ensure the robot remains within its certified workspace. It will be applied to a special class of parallel robots: Spherical Parallel Manipulators (SPM) with coaxial input shafts (CoSPM).

Recommended citation: Alexandre Lê, Fabrice Rouillier, Guillaume Rance, Damien Chablat, Certified kinematic tools for the design and control of parallel robots, Mechanism and Machine Theory, Volume 205, 2025, 105865, ISSN 0094-114X. https://doi.org/10.1016/j.mechmachtheory.2024.105865

On a Software Joint Velocity Limitation of a Spherical Parallel Manipulator with Coaxial Input Shafts

Published in ARK 2024 · International Symposium on Advances in Robot Kinematics, 2024

This article discusses the implementation of a software joint velocity limitation dedicated to a Spherical Parallel Manipulator (SPM) with coaxial input shafts (CoSPM) using a speed control loop. Such an algorithm takes as input the current joint positions as well as the joint reference velocities computed by the speed controller and limit the latter in order to avoid any known singular configuration. This limitation takes into account the workspace properties of the mechanism and the physical characteristics of its actuators. In particular, one takes advantage of the coaxiality of the input shafts of the CoSPM and the resulting unlimited bearing.

Recommended citation: Lê, A., Rance, G., Rouillier, F., Quadrat, A., Chablat, D. (2024). On a Software Joint Velocity Limitation of a Spherical Parallel Manipulator with Coaxial Input Shafts. In: Lenarčič, J., Husty, M. (eds) Advances in Robot Kinematics 2024. ARK 2024. Springer Proceedings in Advanced Robotics, vol 31. Springer, Cham. https://doi.org/10.1007/978-3-031-64057-5_6 https://doi.org/10.1007/978-3-031-64057-5_6

Inertial Line-of-Sight stabilization using a 3-DOF Spherical Parallel Manipulator with coaxial input shafts

Published in OPTRO 2024, 2024

This article dives into the use of a 3-RRR Spherical Parallel Manipulator (SPM) for the purpose of inertial Line Of Sight (LOS) stabilization. Such a parallel robot provides three Degrees of Freedom (DOF) in orientation and is studied from the kinematic point of view. In particular, one guarantees that the singular loci (with the resulting numerical instabilities and inappropriate behavior of the mechanism) are far away from the prescribed workspace. Once the kinematics of the device is certified, a control strategy needs to be implemented in order to stabilize the LOS through the upper platform of the mechanism. Such a work is done with MATLAB Simulink® using a SimMechanics™ model of our robot.

Recommended citation: Alexandre Lê, Guillaume Rance, Fabrice Rouillier, Damien Chablat. Inertial Line-of-Sight stabilization using a 3-DOF Spherical Parallel Manipulator with coaxial input shafts. OPTRO 2024 - 11th International Symposium on Optronics in Defence & Security, Jan 2024, Bordeaux, France. ⟨hal-04483255⟩ https://inria.hal.science/hal-04483255v1

On the Certification of the Kinematics of 3-DOF Spherical Parallel Manipulators

Published in Maple Transactions 2023, 2023

This paper aims to study a specific kind of parallel robot: Spherical Parallel Manipulators (SPM) that are capable of unlimited rolling. A focus is made on the kinematics of such mechanisms, especially taking into account uncertainties (e.g. on conception & fabrication parameters, measures) and their propagations. Such considerations are crucial if we want to control our robot correctly without any undesirable behavior in its workspace (e.g. effects of singularities). In this paper, we will consider two different approaches to study the kinematics and the singularities of the robot of interest: symbolic and semi-numerical. By doing so, we can compute a singularity-free zone in the work- and joint spaces, considering given uncertainties on the parameters. In this zone, we can use any control law to inertially stabilize the upper platform of the robot.

Recommended citation: Alexandre Lê, Damien Chablat, Guillaume Rance, and Fabrice Rouillier. 2023. On the Certification of theKinematics of 3-DOF Spherical Parallel Manipulators. Maple Trans. 3, 2, Article 15660 (August 2023), 17 pages. https://doi.org/10.5206/mt.v3i2.15660