A comprehensive survey of the analytical, numerical and experimental methodologies for dynamics of multibody mechanical systems with clearance or imperfect joints

"Available online 19 December 2017"A comprehensive survey of the literature of the most relevant analytical, numerical, and experimental approaches for the kinematic and dynamic analyses of multibody mechanical systems with clearance joints is presented in this review. Both dry and lubricated clearance joints are addressed here, and an effort is made to include a large number of research works in this particular field, which have been published since the 1960′s. First, the most frequently utilized methods for modeling planar and spatial multibody mechanical systems with clearance joints are analyzed, and compared. Other important phenomena commonly associated with clearance joint models, such as wear, non-smooth behavior, optimization and control, chaos, and uncertainty and links’ flexibility, are then discussed. The main assumptions procedures and conclusions for the different methodologies are also examined and compared. Finally, future developments and new applications of clearance joint modeling and analysis are highlighted.This research was supported in part by the China 111 Project (B16003) and the National Natural Science Foundation of China under Grants 11290151, 11472042 and 11221202. The work was also supported by the Portuguese Foundation for Science and Technology with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

Design of novel generation of rigid revolute, cardan and ball joints

The thesis is focused on the design and fabrication of different joints as part of a team member of three master’s students to design a parallel robot in the fishery. The general approach of how to design a parallel robot is presented. Then, the design and fabrication of a fully articulated snow crab as a model is given in order to use as a test model for the parallel robot. A new design of the revolute joint with a novel concept is presented in this work. The revolute joint with a conical shape uses two sleeves between the joint parts which are coated with Molybdenum Disulfide (MoS₂). The role of MoS₂ is to lubricate the inner parts of the revolute joint. A method for choosing the taper angle is presented based on the application. The authors fabricated the proposed new design at the machine shop of Memorial University and the joint proved to have successful functionality. Afterwards, the design and fabrication of the fork revolute joint, cardan joint (universal joint) and ball joint based on the design of the revolute joint is represented. Overall, the design of different joint types in this thesis is usable not only in the parallel robot but also in many mechanisms and applications

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

Assembly Conditions of Parallel Manipulators Considering Geometric Errors, Joint Clearances, Link Flexibility and Joint Elasticity

International audienceThis paper presents a methodology to analyze the assembly conditions of parallel manipulators and compute the maximum pose errors of their moving platform, while considering geometric errors, joint clearances, link flexibility and joint elasticity. First, the proposed methodology consists in determining the zone(s) of the manipulator workspace in which the manipulator can be assembled assuming that its links and joints are rigid, while taking into account geometric errors and joint clearances. Then, the minimum energy required to assemble the manipulator in the non-assembly zone(s) is computed, while considering link flexibility and joint elasticity. The maximum pose errors of the moving-platform are also computed throughout the manipulator workspace. Finally, a two-dof spatial parallel manipulator, named IRSbot-2, is used as an illustrative example

Experimental stiffness identification in the joints of a lightweight robot

The estimation of stiffness parameters of a robot is of paramount importance for the precision of movement, in fact in the last year the application of robots is justified by many factors, one of these factors is the high precision of movement. The aim of this thesis is to develop a simple experimental methodology for the joint stiffness identification and its application to any robot and also to prove a methods already present in bibliography. The case study in this work is a lightweight robot, namely the UR5 manipulators. Usually these robots are slender and low-weight, and provided with flexible joints, these characteristics shall make a modal analysis of fundamental importance, because the robots that present a high flexibility may generate vibratory phenomenon, that would affect its performance. Therefore the stiffness analysis is the basis and preliminary of modal analysis. The stiffness analysis was made necessary by the lack of knowledge of some UR5 robot parameters as the stiffness, as this thesis’ case, or even damping. In the first three chapters there are, respectively, an introduction on the factors that influence the stiffness in the robotic structures; then are provided all the physical and mathematical knowledges, which underlie the study of stiffness, and finally is illustrated the state of art in stiffness evaluation methods. In the last three chapters there are, respectively, an overview of all components that have been used in laboratory for the evaluation of stiffness, subsequently the value of stiffness are presented respectively through the adopted methodology and the developed methodology, as final step an analysis of results was conducted to compare and to analyze the two methods. Some fundamental conclusions of this work are, respectively, that for conduct an analysis of stiffness is necessary a measurement system with high accuracy, subsequently both the adopted method and developed method may be applied in particular configurations, where the Jacobian matrix don’t change following the load application.Incomin

Metrology Frame for Robotic Machining of Pockets in Large Flexible Panels

RÉSUMÉ Cette recherche présente une nouvelle technologie pour l'usinage robotisé de poches dans les grands panneaux flexibles. Pas d'articles pertinents ont été trouvés dans la littérature, mais un certain nombre de brevets examinés fournis certains des idées de base pour la conception. En particulier, il apparaît essentiel de soutenir le panneau où les forces d'usinage sont appliquées. Pour atteindre cet objectif, un cadre en C est proposé. En appliquant la méthode des éléments finis (MEF) tous les déplacements et les contraintes dans toute la structure sont évalués. Cela révèle que dû à l'effet des forces d'usinage, les deux branches de l'extrémité du cadre en C proposé dévient en sens inverse entraînant une ouverture importante du cadre en C. Pour mesurer cette déviation excessive, un cadre métrologique est conçu où un faisceau laser passe à travers les éléments optiques et atteint un photodétecteur. La position de la tache laser sur la surface du photodétecteur spécifie la distance momentanée entre les deux branches de l'extrémité du cadre en C. Toute déviation due à la force d'usinage affecte cette distance et sera donc détectée par la photodiode afin d'être compensée. Un prototype en bois du cadre en C est construit pour évaluer l'efficacité du cadre de métrologie optique. Les résultats indiquent que la déviation peut être mesurée avec une répétabilité de ± 0,1 mm et une exactitude de ± 0,0884 mm.----------ABSTRACT This thesis presents a new technology for the robotic machining of pockets in large and flexible panels. No relevant research papers were found in the literature but a number of patents are reviewed providing some basic for a conceptual design. In particular, it appears essential to support the panel where machining forces are applied. In order to achieve this goal, a C-frame is proposed. By applying FEA all of the displacements and stresses throughout the structure are evaluated. This reveals that due to machining forces, the two arms of the proposed C-frame deflect in opposite direction resulting in a significant opening of the C-frame. In order to measure this excessive deflection, a metrology frame is designed where a laser beam passes through optical elements and reaches a photodetector. The position of the laser spot on the photodetector surface specifies the momentary distance between the two arms of the C-frame. Any deflection due to machining force affects this distance and therefore will be sensed by the photodiode in order to be compensated. A small version of the C-frame is built from wood to assess the effectiveness of the optical metrology frame. Results indicate that the deflection can be measured with a repeatability of ±0.1 and precision of ±0.0884

The design and analysis of a novel 5 degree of freedom parallel kinematic manipulator.

Masters Degree. University of KwaZulu-Natal, Durban.Abstract available in PDF