Comparison of 3-RPR Planar Parallel Manipulators with regard to their Dexterity and Sensitivity to Geometric Uncertainties

International audienceThis paper deals with the sensitivity analysis of 3-RPR planar parallel manipulators. First, the manipulators under study as well as their degeneracy conditions are presented. Then, an optimization problem is formulated in order to obtain their maximal regular dexterous workspace. Moreover, the sensitivity coefficients of the pose of the manipulator moving platform to variations in the geometric parameters and in the actuated variables are expressed algebraically. Two aggregate sensitivity indices are determined, one related to the orientation of the manipulator moving platform and another one related to its position. Then, we compare two non-degenerate and two degenerate 3-R\underline{P}R planar parallel manipulators with regard to their dexterity, workspace size and sensitivity. Finally, two actuating modes are compared with regard to their sensitivity

Sensitivity analysis of 3-RPR planar parallel manipulators

International audienceThis paper deals with the sensitivity analysis of 3-RPR planar parallel manipulators (PPMs). First, the sensitivity coefficients of the pose of the manipulator moving platform to variations in the geometric parameters and in the actuated variables are expressed algebraically. Moreover, two aggregate sensitivity indices are determined, one related to the orientation of the manipulator moving platform and another one related to its position. Then, a methodology is proposed to compare 3-RPR PPMs with regard to their dexterity, workspace size and sensitivity. Finally, the sensitivity of a 3-RPR PPM is analyzed in detail and four 3-RPR PPMs are compared as illustrative examples

Comparing structural airframe maintenance strategies based on probabilistic estimates of the remaining useful service life

Structural airframe maintenance is a subset of aircraft maintenance, which is often performed at scheduled intervals to detect and repair cracks that would otherwise affect the safety of the aircraft. With the progress of structural health monitoring (SHM) techniques, which uses on-board sensors and actuators to assess damage status, condition-based maintenance (CBM) is considered as an alternative to traditional scheduled maintenance. By applying SHM techniques, CBM can access damages status as frequently as needed and unscheduled maintenance can be asked once the damage exceeds a particular threshold. Due to the harsh working environment and sensor limitation, the measurement data acquired from SHM is often quite noisy. In this paper, Extended Kalman filter is used to filer the noise to provide an accurate estimation of crack size and crack growth parameters together with their associated uncertainty. This knowledge is used to obtain a probabilistic estimate of the remaining useful service life of the structure. Based on these estimates, two maintenance philosophies are developed and further compared in terms of maintenance stop number or replaced panel number. The results indicate that both these two strategies reduce considerably the maintenance stop number compared to scheduled maintenance

Sensitivity analysis of a suspended CDPR to design parameters

Cable Driven Parallel Robots (CDPR) are systems driven exclusively by cables, giving them advantages in operation and use. However, this also introduces complexity into their mechanical behavior. Indeed, a cable is non-rigid, so it bends and lengthens in response to external forces. In addition, its elasticity is affected by a hysteresis phenomenon. This paper first introduces a new modelling of CDPRs allowing to take in consideration the deflection and elongation of the cables within the actuating chain while considering the pulleys. In a second step, a design of experiments is conducted on a suspended CDPR with four cables. This allows to quantify the effects on the theoretical MP pose error of important design parametres that are the type of pulley joint, cable' Young's modulus, the cable mass and the Mobile Platform (MP) mass. Interaction between theses parameters is also studied. This study is conducted for different sizes of CDPR. It appears that the variation of the Young's modulus and the MP mass has a significant impact on the theoretical MP pose error regardless of the size of the CDPR. based on the obtained results, the type of pulley joint seems to have very little influence on the theoretical MP pose error. It is also shown that the cable mass should be taken into account when modelling CDPRs over 10m

Etude des Conditions d'Assemblage de Manipulateurs Hyperstatiques : application à un manipulateur 5 barres

Un manipulateur hyperstatique est difficile à assembler dès lors que certains paramètres géométriques ne sont pas égaux à leur valeur nominale. L'assemblage se fait dans ce cas au moyen de la déformation des corps et/ou des jeux dans les liaisons. Il se peut même que l'assemblage ne soit pas possible lorsque les variations des paramètres géométriques sont trop importantes. Cet article vise ainsi à étudier les conditions d'assemblage de manipulateurs parallèles hyperstatiques en présence de variations dans les paramètres géométriques et de jeux dans les liaisons

The Kinematic Sensitivity of Robotic Manipulators to Joint Clearances

Volume 2: 34th Annual Mechanisms and Robotics Conference, Parts A and BMontreal, Quebec, Canada, August 15–18, 2010Conference Sponsors: Design Engineering Division and Computers in Engineering DivisionISBN: 978-0-7918-4410-6 | eISBN: 978-0-7918-3881-5International audienceThe paper deals with the kinematic sensitivity of robotic manipulators to joint clearances. First, an error prediction model applicable to both serial and parallel manipulators is developed. A clearance model associated with axisymmetrical joints, which are widely used in robotic manipulators, is also proposed. Then, two nonconvex quadratically constrained quadratic programs~(QCQPs) are formulated in order to find the maximum reference-point position error and the maximum orientation error of the moving-platform for given joint clearances. Finally, the contributions of the paper are highlighted by means of two illustrative examples

Sensitivity Analysis of a Suspended Cable-Driven Parallel Robot to Design Parameters

International audienceAbstract Cable-Driven Parallel Robots (CDPRs) are systems driven exclusively by cables, giving them advantages in operation. However, this also introduces complexity into their mechanical behavior. Indeed, the cable elasticity is affected by a hysteresis phenomenon. There is therefore an uncertainty about the actual value of the cable's Young's modulus. However, uncertainty analysis on design parameters of CDPR has not been conducted yet. So, this paper first introduces a new modeling of CDPRs allowing to take in consideration the sagging of the cables while considering different pulley architectures as well as the cable dead length between the winch and the pulley. Then, a sensitivity analysis of the main design parameters on the positioning error of the Moving-Platform (MP) is performed through a design of experiments conducted on a suspended CDPR with four cables. For this purpose, the variation of the Young's modulus of the cables is determined. This allows to quantify and to rank the effects on the theoretical MP pose error of important design parameters that are the type of pulley joint, cable's Young's modulus, the cable mass and the MP mass. This study is conducted for different sizes of CDPR. The results obtained show that the evolution of the effects of the design parameters is not the same depending on the size of the CDPR. Technical major considerations are derived from the presented results as guidelines for CDPR designer, keeping the modeling relatively simple but robust enough for real-time control of CDPRs

Conception et développement d’un robot hexapode autonome à muscles artificiels en matériau à mémoire de forme

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