Dynamic Parameter Identification of Actuation Redundant Parallel Robots: Application to the DualV

International audienceOff-line robot dynamic identification methods are based on the use of the Inverse Dynamic Identification Model (IDIM), which calculates the joint forces/torques (estimated as the product of the known control signal - the input reference of the motor current loop - by the joint drive gains) that are linear in relation to the dynamic parameters, and on the use of linear least squares technique to calculate the parameters (IDIM-LS technique). However, as actuation redundant parallel robots are over-constrained, their IDIM has infinity of solutions for the force/torque prediction, depending on the value of the desired overconstraint that is a priori unknown in the identification process. As a result, the IDIM cannot be used as it. This paper proposes a modified formulation for the IDIM of actuation redundant robots that can be used for identification purpose. This formulation consists of projecting the input torques/forces on the platform coordinates, thus leading to a unique solution of the model that can thus be used in the identification process. The identification of the inertial parameters of a planar parallel robot with actuation redundancy, the DualV, is then carried out using this modified IDIM. Experimental results show the validity of the method

Elasto-geometrical modeling and calibration of redundantly actuated PKMs

International audienceRedundantlyactuated parallel kinematic machines (PKMs) offer a number of advantages compared to classical non-redundant PKMs. Particularly, they show a better stiffness thanks to singularity avoidance and they have an improved repeatability due to a better behavior against backlashes. The main problem with the calibration of these machines is that the redundancy leads to some mechanical strains in their structure. This makes it difficult to identify the geometrical errors of their structure without taking into account the effects of the elastic deformations. The main originality of this work is to propose an efficient elasto-geometrical and calibration method that allows the identification of both the geometrical and stiffness parameters of redundantlyactuated parallel mechanisms with slender links. The first part of the paper explains the proposed method through its application on a simple redundant planar mechanism. The second part deals with its experimental application to the redundant Scissors Kinematics machine

Analysis of collocated feedback controllers for four-bar planar mechanisms with joint clearances

International audienceThis article presents an analysis of two-dimensional four-bar mechanisms with joint clearance, when one joint is actuated by collocated open-loop or state feedback controllers (proportional-derivative, state feedback linearization, passivity-based control). The study is led with numerical simulations obtained with a projected Moreau-Jean's event-capturing algorithm. The contact/impact model uses kinematic coefficients of restitution, and Coulomb's friction. The focus is put on how much the performance deteriorates when clearances are added in the joints. It is shown that collocated feedback controllers behave in a very robust way

Synthèse cinématique d'un octopode parallèle sans surcontrainte avec conditions de singularité simples

Ce mémoire présente l'étude du lieu des singularités de type II pour un mécanisme parallèle cinématiquement redondant à (6+2) degrés de liberté dont l'architecture est préalablement donnée. Cette étude se concentre sur les conditions mathématiques telles que le déterminant de la matrice jacobienne s'annule pour toutes configurations dues à la mobilité interne du mécanisme permise par la redondance cinématique. Pour ce faire, la construction d'une matrice partageant les mêmes conditions de singularité que la matrice jacobienne du mécanisme est présentée. La réécriture du déterminant de cette matrice par une sommation de quatre sous-déterminants pondérée par les paramètres de mobilité interne du mécanisme mène à un système d'équations non linéaires à résoudre pour obtenir le lieu des singularités. Une méthode d'élimination de variables, le résultant des polynômes, est ensuite appliquée de manière récursive à ce système d'équations afin d'en extraire les conditions pouvant le résoudre. Les lieux de singularité sont ensuite analysés suivant deux cas de figure. Le premier se penche sur les configurations spécifiques du mécanisme où l'angle de torsion de la plateforme est nul, et le second se concentre sur le cas général, où cet angle de torsion n'est pas nécessairement nul. Dans le premier cas d'analyse, il est montré que les lieux de singularité se situent à l'extérieur de l'espace atteignable du mécanisme cinématiquement redondant. Dans le second cas d'analyse, il est montré que l'espace en orientation demeure quelque peu affecté par la présence de singularités, bien que leur localisation par des équations mathématiques analytiques simples soit possible. Finalement, une comparaison graphique des espaces atteignables en orientation entre le mécanisme cinématiquement redondant et le mécanisme non redondant standard est effectuée afin de visualiser l'impact de l'ajout de la redondance cinématique sur l'agrandissement de l'espace en orientation.This thesis presents the study of the type II singularity locus of a kinematically redundant(6+2) degree-of-freedom parallel mechanism whose architecture is prescribed. This studyfocuses on the mathematical conditions for which the determinant of the Jacobian matrixvanishes for all configurations of the internal mobility in the mechanism due to its kinematicredundancy. To do so, a matrix that captures the same conditions of singularity as the Jacobian matrix is presented. The expansion of the determinant of the aforementioned matrixinto a weighted sum of four sub-determinants whose weighting factors correspond to theinternal mobility parameters leads to a nonlinear system of equations whose solution yieldsthe locus of singularity. A method of elimination theory, the resultant of polynomials, isapplied afterwards on the system of equations in a recursive manner to extract the mathematical conditions corresponding to the solution. The loci of singularity are then analyzedfollowing two cases. The first case focuses on the specific configurations of the mechanismwhere the torsion angle of the platform is zero, whereas the second case takes into accountthe general configurations, i.e. the configurations in which the torsion angle is not necessarily zero. In the former case of analysis, it is shown that the loci of singularity lie outsideof the reachable orientational workspace of the kinematically redundant mechanism. In thelatter case of analysis, it is presented that the orientational workspace is still somewhat restrained by singularities, yet their localization by simple analytical mathematical equationsis possible. Finally, a graphical comparison of the orientational reachable workspace of thekinematically redundant mechanism and that of the standard non-redundant mechanism isperformed to visualize the impact of the kinematic redundancy on the enhancement of theorientational workspace

The 29th Aerospace Mechanisms Symposium

The proceedings of the 29th Aerospace Mechanisms Symposium, which was hosted by NASA Johnson Space Center and held at the South Shore Harbour Conference Facility on May 17-19, 1995, are reported. Technological areas covered include actuators, aerospace mechanism applications for ground support equipment, lubricants, pointing mechanisms joints, bearings, release devices, booms, robotic mechanisms, and other mechanisms for spacecraft