Changing Assembly Modes without Passing Parallel Singularities in Non-Cuspidal 3-R\underline{P}R Planar Parallel Robots

This paper demonstrates that any general 3-DOF three-legged planar parallel robot with extensible legs can change assembly modes without passing through parallel singularities (configurations where the mobile platform loses its stiffness). While the results are purely theoretical, this paper questions the very definition of parallel singularities.Comment: 2nd International Workshop on Fundamental Issues and Future Research Directions for Parallel Mechanisms and Manipulators, Montpellier : France (2008

Minimal Representation for the Control of Gough-Stewart Platforms via Leg Observation Considering a Hidden Robot Model

International audienceThis paper presents new insights about the sensor-based control of Gough-Stewart (GS) platforms. Previous works have shown that it was possible to control the GS platform by observing its legs directions instead of using the encoders values or the measurement of the platform pose. It was demonstrated that observing only three legs directions was enough for the control but no physical explanations were given. Moreover, sometimes, the GS platform was not converging to the desired pose and the reasons of these divergences were not disclosed. This paper aims at answering to this two opened problems. It is shown that observing three leg directions involves controlling the displacement of a hidden robot whose models differs from those of the usual GS platform. This robot has assembly modes and singular configurations different from those of the GS platform. This involves that the legs to observe should be chosen carefully in order to avoid inaccuracy problems. In this sense, the accuracy analysis of the new robot is performed to show the importance of the leg selection. All these results are validated on a GS platform simulator created using ADAMS/Controls and interfaced with Matlab/Simulink

Minimal Representation for the Control of the Adept Quattro with Rigid Platform via Leg Observation Considering a Hidden Robot Model

International audiencePrevious works on the Gough-Stewart (GS) platform have shown that its visual servoing using the observation of its leg directions was possible by observing only three of its six legs but that the convergence to the desired pose was not guarantied. This can be explained by considering that the visual servoing of the leg direction of the GS platform was equivalent to controlling another robot, the 3-UPS that has assembly modes and singular configurations different from those of the GS platform. Considering this hidden robot model allowed the simplification of the singularity analysis of the mapping between the leg direction space and the Cartesian space. In this paper, the work on the definition of the hidden robot models involved in the visual servoing using the observation of the robot leg directions is extended to another robot, the Adept Quattro. It will be shown that the hidden robot model is completely different from the model involved in the control of the GS platform. Therefore, the results obtained for the GS platform are not valuable for this robot. The hidden robot has assembly modes and singular configurations different from those of the Quattro. An accuracy analysis is performed to show the importance of the leg selection. All these results are validated on a Quattro simulator created using ADAMS/Controls and interfaced with Matlab/Simulink

Analysis of the Dynamic Performance of Serial 3R Orthogonal Manipulators

International audienceSerial 3R orthogonal manipulators have been studied recently and it has been proved that they can exhibit good performances in term of workspace size and kinematic properties. The aim of this work is to analyze their dynamic performances, and compare them with anthropomorphic manipulators, which are very popular in industry. Static and dynamic analyses based on the evaluation of the maximal input torques required for moving the manipulator are achieved. It is shown that, as in kinematics, the dynamic performances of the serial 3R orthogonal manipulators are better

Self-Motions of General 3-RPR Planar Parallel Robots

This paper studies the kinematic geometry of general 3-RPR planar parallel robots with actuated base joints. These robots, while largely overlooked, have simple direct kinematics and large singularity-free workspace. Furthermore, their kinematic geometry is the same as that of a newly developed parallel robot with SCARA-type motions. Starting from the direct and inverse kinematic model, the expressions for the singularity loci of 3-RPR planar parallel robots are determined. Then, the global behaviour at all singularities is geometrically described by studying the degeneracy of the direct kinematic model. Special cases of self-motions are then examined and the degree of freedom gained in such special configurations is kinematically interpreted. Finally, a practical example is discussed and experimental validations performed on an actual robot prototype are presented

Constraint Singularity-Free Design of the IRSBot-2

International audienceThis paper deals with the constraint analysis of a novel two-degree-of-freedom (DOF) spatial translational parallel robot for high-speed applications named the IRSBot-2 (acronym for IRCCyN Spatial Robot with 2 DOF). Unlike most two-DOF robots dedicated to planar translational motions this robot has two spatial kinematic chains that provide a very good intrinsic stiffness. First, the robot architecture is presented and its constraint singularity conditions are given. Then, its constraint singularities are analyzed in its parameter space based on a cylindrical algebraic decomposition. Finally, a deep analysis is carried out in order to determine the sets of design parameters of the IRSBot-2 that prevent it from reaching any constraint singularity. To the best of our knowledge, such an analysis is performed for the first time

Increasing energy efficiency of high-speed parallel robots by using variable stiffness springs and optimal motion generation

International audienceThe classical approach to decrease the energy consumption of high-speed robots is by lowering the moving elements mass in order to have a lightweight structure. Even if this allows reducing the energy consumed, the lightweight architecture affects the robot stiffness, worsening the accuracy of the mechanism. Recently, variable stiffness actuators (VSAs) have been used in order to reduce the energy consumption of high-speed pick-and-place robots. The idea is to smartly tune online the stiffness of VSA springs so that the robot is put in near a resonance mode, thus considerably decreasing the energy consumption during fast pseudo-periodic pick-and-place motions. However, the serial configuration of springs and motors in the VSA leads to uncontrolled robot deflections at high-speeds and, thus, to a poor positioning accuracy of its end-effector. In order to avoid these drawbacks and to increase the energy efficiency while ensuring the accuracy, this paper proposes the use of parallel arrangement of variable stiffness springs (VSS) and motors, combined with an energy-based optimal trajectory planner. The VSS are used as energy storage for carrying out the reduction of the energy consumption and their parallel configuration with the motors ensure the load balancing at high-speed without losing the accuracy of the robot. Simulations of the suggested approach on a five-bar mechanism are performed and show the increase on energy efficiency. 1 INTRODUCTION It is well-known that in industrial applications, such as high-speed pick-and-place operations, parallel robots are widely used [1, 2]. Repeatability and accuracy are typically the most important criteria to measure their performance. Nevertheless, the design trends to operate at high speeds are shifting to the design of robots with lightweight architectures [3] in order to decrease the energy consumed by the motors, and measure as well the robot performance based on its energy efficiency [4]. For slow motions, gravity-balancing techniques [5-8] have been proposed in order to compensate the input efforts required to move the links of a pick-and-place robot, and thus to avoid consuming energy. Even if these methods have shown their effectiveness at slow speeds, it is not the case for high-speed operations in which the inertial effects are preponderant. A first solution introduced the series elastic actuators (SEAs) [9] to cope with the energy storage issues. The SEAs are compliant actua-tors composed by a motor which is linked to a spring in series that serves as energy storage, and whose stiffness is set by the spring constant. SEAs were first used to absorb contact shocks and to reduce the peak forces due to the impacts in bipedal walking robots [10]. The limitation of the SEAs is that the stiffness is fixed and cannot be altered during motion, thus limiting the level of compliance to adapt for different tasks. Therefore, a recent second solution proposed the use of variable stiffness actuators (VSAs) [11-13] to handle with energy storage issues. VSAs co

IRSBOT-2: A Novel Two-Dof Parallel Robot for High-Speed Operations

International audienceThis paper presents a novel two-degree-of-freedom (DOF) translational parallel robot for high-speed applications named the IRSBot-2 (acronym for IRCCyN Spatial Robot with 2 DOF). Unlike most two-DOF robots dedicated to planar translational motions, this robot has two spatial kinematic chains which confers a very good intrinsic stiffness. First, the robot architecture is described. Then, its actuation and constraint singularities are analyzed. Finally, the IRSBot-2 is compared to its two-DOF counterparts based on elastostatic performances

Globalizing curriculum beyond the classroom: Service Learning Programs benefit Students, impact local issues and answer local needs to build bridges between cultures

[EN] Based on a case study, this article analyzes the effects of introducing Service Learning in the curriculum of a study abroad US Center. Explaining institutional motivations as well as resistances, this research shows that this introduction was essentially academic in nature, and represented an innovative way to some perceived deficiencies in the acquisition of learning objectives by students. This research also indicates the specific conditions in which this type of Service Learning can thrive, such as a strong welfare state context, which is both a support and a potential issue, and the necessity to have students supervised in their service by local managers. More general lessons are drawn for a successful practice of Service Learning abroad: clearly defined academic goals, strict distinction between Service Learning and other forms of volunteering or experiential learning, ethical rules to prevent patronizing attitudes among volunteers.Briot, P.; Ponson, L.; Leterre, T. (2019). Globalizing curriculum beyond the classroom: Service Learning Programs benefit Students, impact local issues and answer local needs to build bridges between cultures. En HEAD'19. 5th International Conference on Higher Education Advances. Editorial Universitat Politècnica de València. 727-734. https://doi.org/10.4995/HEAD19.2019.9417OCS72773