Design of a Parallel Robotic Manipulator using Evolutionary Computing

In this paper the kinematic design of a 6‐dof parallel robotic manipulator is analysed. Firstly, the condition number of the inverse kinematic jacobian is considered as the objective function, measuring the manipulator’s dexterity and a genetic algorithm is used to solve the optimization problem. In a second approach, a neural network model of the analytical objective function is developed and subsequently used as the objective function in the genetic algorithm optimization search process. It is shown that the neuro‐genetic algorithm can find close to optimal solutions for maximum dexterity, significantly reducing the computational burden. The sensitivity of the condition number in the robot’s workspace is analysed and used to guide the designer in choosing the best structural configuration. Finally, a global optimization problem is also addressed

Singularity-free workspace analysis and geometric optimization of parallel mechanisms

Les mécanismes parallèles sont fréquemment utilisés comme robots manipulateurs, comme simulateurs de mouvement, comme machines parallèles, etc. Cependant, à cause des chaînes cinématiques fermées qui caractérisent leur architecture, le mouvement de leur plateforme est limité et des singularités cinématiques complexes peuvent apparaître à l'intérieur de leur espace de travail. Par conséquent, une maximisation l'espace de travail libre de singularité pour ce type de mécanismes est souhaitable dans un contexte de conception. Dans cette thèse, deux types de mécanismes parallèles sont étudiés: les mécanismes parallèles plans ?avec, en particulier le 3-RPR? et les mécanismes spatiaux ?avec, en particulier, la plateforme de Gough-Stewart. Pour chaque type de mécanisme parallèle, une forme simple d'équation de singularité est obtenue. Le principe consiste à séparer l'origine O' du repère mobile du point considéré P et de faire coïncider O' avec un point particulier de la plateforme. L'équation ainsi obtenue est l'équation de singularité du point P de la plateforme qui contient un ensemble minimal de paramètres géométriques. Par ailleurs, il est prouvé que les centres des cercles et sphères définissant l'espace de travail se trouvent exactement sur les lieux de singularité. Cette observation et l'équation de singularité simplifiée constituent les points de départ de l'analyse de l'espace de travail libre de singularité ainsi que de l'optimisation géométrique. Pour le mécanisme parallèle plan 3-RPR, l'espace de travail libre de singularité et les limites correspondantes pour la longueur des pattes dans une orientation prescrite sont déterminés. Ensuite l'architecture optimale qui permet d'obtenir un espace de travail maximal tout en étant libre de singularité est discutée. En ce qui concerne la plateforme de Gough-Stewart, cette thèse se concentre sur le manipulateur symétrique simplifié minimal (MSSM). Comme une plateforme de Gough- Stewart a 6 degrés de liberté, son espace de travail se divise en deux: l'espace de travail en position (ou simplement espace de travail) et l'espace de travail en orientation. A partir de l'équation de singularité simplifiée, une procédure générale est développée afin de déterminer l'espace de travail libre de singularité maximal autour d'un point particulier dans une orientation donnée, et afin de déterminer les limites correspondantes des longueurs de patte. Dans le but de maximiser l'espace de travail libre de singularité en orientation, un algorithme est présenté qui optimise les trois angles d'orientation. Sachant qu'une plateforme fonctionne habituellement pour une certaine gamme d'orientations, deux algorithmes qui calculent l'espace de travail en orientation libre de singularité maximal sont présentés. En utilisant les angles d'Euler en roulis, tangage et lacet, l'espace de travail en orientation pour une position prescrite peut être défini par 12 surfaces. Basé sur ce fait, un algorithme numérique est présenté qui évalue et représente l'espace de travail en orientation pour une position prescrite dans les limites données de longueur de patte. Ensuite, une procédure est proposée afin de déterminer l'espace de travail en orientation libre singularité maximal ainsi que les limites correspondantes des longueurs de patte. En pratique, une plateforme peut fonctionner dans un ensemble de positions. Ainsi, l'effet de la position de travail sur l'espace de travail en orientation libre de singularité maximal est analysé et deux algorithmes sont proposés pour calculer ce dernier pour tout un ensemble de positions particulières. Finalement, un algorithme qui optimise les paramètres géométriques est développé dans le but de déterminer l'architecture optimale qui permet à la plateforme de MSSM Gough-Stewart d'obtenir l'espace de travail libre singularité maximal autour d'une position particulière pour l'orientation de référence. Les résultats obtenus peuvent être utilisés pour la conception géométrique, la configuration des paramètres (longueur des pattes) ou la planification de trajectoires libres de singularité des mécanismes parallèles considérés. En outre, les algorithmes proposés peuvent également être appliqués à d'autres types de mécanismes parallèles

Numerical computation and avoidance of manipulator singularities

This thesis develops general solutions to two open problems of robot kinematics: the exhaustive computation of the singularity set of a manipulator, and the synthesis of singularity-free paths between given configurations. Obtaining proper solutions to these problems is crucial, because singularities generally pose problems to the normal operation of a robot and, thus, they should be taken into account before the actual construction of a prototype. The ability to compute the whole singularity set also provides rich information on the global motion capabilities of a manipulator. The projections onto the task and joint spaces delimit the working regions in such spaces, may inform on the various assembly modes of the manipulator, and highlight areas where control or dexterity losses can arise, among other anomalous behaviour. These projections also supply a fair view of the feasible movements of the system, but do not reveal all possible singularity-free motions. Automatic motion planners allowing to circumvent problematic singularities should thus be devised to assist the design and programming stages of a manipulator. The key role played by singular configurations has been thoroughly known for several years, but existing methods for singularity computation or avoidance still concentrate on specific classes of manipulators. The absence of methods able to tackle these problems on a sufficiently large class of manipulators is problematic because it hinders the analysis of more complex manipulators or the development of new robot topologies. A main reason for this absence has been the lack of computational tools suitable to the underlying mathematics that such problems conceal. However, recent advances in the field of numerical methods for polynomial system solving now permit to confront these issues with a very general intention in mind. The purpose of this thesis is to take advantage of this progress and to propose general robust methods for the computation and avoidance of singularities on non-redundant manipulators of arbitrary architecture. Overall, the work seeks to contribute to the general understanding on how the motions of complex multibody systems can be predicted, planned, or controlled in an efficient and reliable way.Aquesta tesi desenvolupa solucions generals per dos problemes oberts de la cinemàtica de robots: el càlcul exhaustiu del conjunt singular d'un manipulador, i la síntesi de camins lliures de singularitats entre configuracions donades. Obtenir solucions adequades per aquests problemes és crucial, ja que les singularitats plantegen problemes al funcionament normal del robot i, per tant, haurien de ser completament identificades abans de la construcció d'un prototipus. La habilitat de computar tot el conjunt singular també proporciona informació rica sobre les capacitats globals de moviment d'un manipulador. Les projeccions cap a l'espai de tasques o d'articulacions delimiten les regions de treball en aquests espais, poden informar sobre les diferents maneres de muntar el manipulador, i remarquen les àrees on poden sorgir pèrdues de control o destresa, entre d'altres comportaments anòmals. Aquestes projeccions també proporcionen una imatge fidel dels moviments factibles del sistema, però no revelen tots els possibles moviments lliures de singularitats. Planificadors de moviment automàtics que permetin evitar les singularitats problemàtiques haurien de ser ideats per tal d'assistir les etapes de disseny i programació d'un manipulador. El paper clau que juguen les configuracions singulars ha estat àmpliament conegut durant anys, però els mètodes existents pel càlcul o evitació de singularitats encara es concentren en classes específiques de manipuladors. L'absència de mètodes capaços de tractar aquests problemes en una classe suficientment gran de manipuladors és problemàtica, ja que dificulta l'anàlisi de manipuladors més complexes o el desenvolupament de noves topologies de robots. Una raó principal d'aquesta absència ha estat la manca d'eines computacionals adequades a les matemàtiques subjacents que aquests problemes amaguen. No obstant, avenços recents en el camp de mètodes numèrics per la solució de sistemes polinòmics permeten ara enfrontar-se a aquests temes amb una intenció molt general en ment. El propòsit d'aquesta tesi és aprofitar aquest progrés i proposar mètodes robustos i generals pel càlcul i evitació de singularitats per manipuladors no redundants d'arquitectura arbitrària. En global, el treball busca contribuir a la comprensió general sobre com els moviments de sistemes multicos complexos es poden predir, planificar o controlar d'una manera eficient i segur

Space Frames with Multiple Stable Configurations

This paper is concerned with beamlike spaceframes that include a large number of bistable elements, and exploit the bistability of the elements to obtain structures with multiple stable configurations. By increasing the number of bistable elements, structures with a large number of different configurations can be designed. A particular attraction of this approach is that it produces structures able to maintain their shape without any power being supplied. The first part of this paper focuses on the design and realization of a low-cost snap-through strut, whose two different lengths provide the required bistable feature. A parametric study of the length-change of the strut in relation to the peak force that needs to be applied by the driving actuators is carried out. Bistable struts based on this concept have been made by injection molding nylon. Next, beamlike structures based on different architectures are considered. It is shown that different structural architectures produce structures with workspaces of different size and resolution, when made from an identical number of bistable struts. One particular architecture, with 30 bistable struts and hence over 1 billion different configurations, has been demonstrated

Analytical Workspace, Kinematics, and Foot Force Based Stability of Hexapod Walking Robots

Many environments are inaccessible or hazardous for humans. Remaining debris after earthquake and fire, ship hulls, bridge installations, and oil rigs are some examples. For these environments, major effort is being placed into replacing humans with robots for manipulation purposes such as search and rescue, inspection, repair, and maintenance. Mobility, manipulability, and stability are the basic needs for a robot to traverse, maneuver, and manipulate in such irregular and highly obstructed terrain. Hexapod walking robots are as a salient solution because of their extra degrees of mobility, compared to mobile wheeled robots. However, it is essential for any multi-legged walking robot to maintain its stability over the terrain or under external stimuli. For manipulation purposes, the robot must also have a sufficient workspace to satisfy the required manipulability. Therefore, analysis of both workspace and stability becomes very important. An accurate and concise inverse kinematic solution for multi-legged robots is developed and validated. The closed-form solution of lateral and spatial reachable workspace of axially symmetric hexapod walking robots are derived and validated through simulation which aid in the design and optimization of the robot parameters and workspace. To control the stability of the robot, a novel stability margin based on the normal contact forces of the robot is developed and then modified to account for the geometrical and physical attributes of the robot. The margin and its modified version are validated by comparison with a widely known stability criterion through simulated and physical experiments. A control scheme is developed to integrate the workspace and stability of multi-legged walking robots resulting in a bio-inspired reactive control strategy which is validated experimentally

A bibliometric overview of Mechanism and Machine Theory journal: publication trends from 1990 to 2020

This work reports a bibliometric overview of Mechanism and Machine Theory journal in the timespan 1990-2020. This desideratum is achieved by considering the most relevant features associated with the life of this scientific journal, namely in terms of publications, citations, regions of origin of publications, authors, institutions, etc. In the present study, the Scopus database was chosen as the platform to identify and extract information on those aspects. Thus, based on the data collected, a comprehensive bibliometric analysis of Mechanism and Machine Theory is performed, which permits to reveal the overall picture of the journal trends in evolution, as well as its impact and influence in the mechanism and machine science community. Overall, the outcomes presented in this study allow to observe that Mechanism and Machine Theory journal has been attracting more and more interest year after year.FCT -Fundação para a Ciência e a Tecnologia(UIDB/04436/2020

Pressure-Constrained, Reduced-DOF, Interconnected Parallel Manipulators with Applications to Space Suit Design

This dissertation presents the concept of a Morphing Upper Torso, an innovative pressure suit design that incorporates robotic elements to enable a resizable, highly mobile and easy to don/doff spacesuit. The torso is modeled as a system of interconnected, pressure-constrained, reduced-DOF, wire-actuated parallel manipulators, that enable the dimensions of the suit to be reconfigured to match the wearer. The kinematics, dynamics and control of wire-actuated manipulators are derived and simulated, along with the Jacobian transforms, which relate the total twist vector of the system to the vector of actuator velocities. Tools are developed that allow calculation of the workspace for both single and interconnected reduced-DOF robots of this type, using knowledge of the link lengths. The forward kinematics and statics equations are combined and solved to produce the pose of the platforms along with the link tensions. These tools allow analysis of the full Morphing Upper Torso design, in which the back hatch of a rear-entry torso is interconnected with the waist ring, helmet ring and two scye bearings. Half-scale and full-scale experimental models are used along with analytical models to examine the feasibility of this novel space suit concept. The analytical and experimental results demonstrate that the torso could be expanded to facilitate donning and doffing, and then contracted to match different wearer's body dimensions. Using the system of interconnected parallel manipulators, suit components can be accurately repositioned to different desired configurations. The demonstrated feasibility of the Morphing Upper Torso concept makes it an exciting candidate for inclusion in a future planetary suit architecture

Bringing Biophilic Architecture into Business Parks Design Towards Enhancing Users Experience

Recently, most people have spent much of their time at work, often in indoor office buildings that are designed without regard to natural elements and workers` well-being. For these reasons, Business Parks are designed to improve the whole workplace environment. Bringing fresh air, green areas, and natural elements into workspaces could enhance the work environment and increase productivity by taking care of workers` physiological needs. On other hand, Biophilic design introduces some principles to create visually beautiful and spiritual places. By merging Architecture with nature and bringing outdoors greenery through indoor areas, a healthy workplace environment could be generated. Therefore, Biophilic design could be a solution towards more relaxed workspaces. Consequently, this study will elaborate a comprehensive framework towards combining principles, attributes, and elements of Biophilic design and design solutions of Business Parks. The study focuses on Business Park as a case study as the trend of Business Park can change the traditional concept of office buildings and reconnect the human with nature again, which lessens stress and negative impacts on health. So that, workers can get a work environment free from stress which will enhance the individuals` well-being. In this context, this paper will analyze international, local offices and Business Parks that were designed upon Biophilic design concepts. Eventually, the novelty aim of this manuscript is to create a contemporary tendency which concerns about blending the Biophilic design concept with Business Parks interior and exterior design spaces to create an efficient and healthy work environment, also to improve the whole users` experience

On the design of multi-platform parallel mechanisms

Parallel mechanisms have been examined in more and more detail over the past two decades. Parallel mechanisms are essentially the same design layout, a base, multiple legs/limbs, and a moving platform with a single end-effector to allow the mechanism to complete its desired function. Recently, several research groups have begun looking into multiple-platform parallel mechanisms and/or multiple end-effectors for parallel mechanisms. The reason for the research in this new form of parallel mechanism stems from multiple sources, such as applications that would require multiple handling points being accessed simultaneously, a more controlled gripper motion by having the jaws of the gripper being attached at different platforms, or to increasing the workload of the mechanism. The aim of the thesis is to modify the design process of parallel mechanisms so that it will support the development of a new parallel mechanism with multiple platforms capable of moving relative to each other in at least 1-DOF and to analyse the improvements made on the traditional single platform mechanism through a comparison of the power requirements for each mechanism. Throughout the thesis, a modified approach to the type synthesis of a parallel mechanism with multiple moving platforms is proposed and used to create several case study mechanisms. Additionally, this thesis presents a new series of methods for determining the workspace, inverse kinematic and dynamic models, and the integration of these systems into the design of a control system. All methods are vetted through case studies where they are judged based on the results gained from existing published data. Lastly, the concepts in this thesis are combined to produce a physical multi-platform parallel mechanism case study with the process being developed at each stage. Finally, a series of proposed topics of future research are listed along with the limitations and contributions of this work