Singularity Analysis for a 5-DoF FullySymmetrical Parallel Manipulator 5-RRR (RR

Abstract-A 5-DoF 3R2T (three dimensional rotation and two dimensional translation degrees of freedom) fully-symmetrical parallel manipulator can be adopted in many applications such as simulating the motion of spinal column. However, kinematics of this type parallel manipulator has not been studied enough because of short history. The study of kinematics of the manipulators leads inevitably to the problem of singular configuration. Singularity of a 5-DoF 3R2T fully-symmetrical parallel manipulator, 5-RRR(RR), is illustrated in this study. According to the singularity classification by Fang and Tsai, both limb singularity and actuation singularity are illustrated by screw theory and Grassmann geometry. The result of this study will be helpful for singularity analysis of 5-DoF 3R2T fully-symmetrical parallel manipulators because of their similar constraint property

Symmetric Subspace Motion Generators

When moving an object endowed with continuous symmetry, an ambiguity arises in its underlying rigid body transformation, induced by the arbitrariness of the portion of motion that does not change the overall body shape. The functional redundancy caused by continuous symmetry is ubiquitously present in a broad range of robotic applications, including robot machining and haptic interface (revolute symmetry), remote center of motion devices for minimal invasive surgery (line symmetry), and motion modules for hyperredundant robots (plane symmetry). In this paper, we argue that such functional redundancy can be systematically resolved by resorting to symmetric subspaces (SSs) of the special Euclidean group SE(3), which motivates us to systematically investigate the structural synthesis of SS motion generators. In particular, we develop a general synthesis procedure that allows us to generate a wide spectrum of novel mechanisms for use in the applications mentioned

Contribuições para o projeto de manipuladores paralelos através da síntese do tipo

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2011A Síntese do Tipo é uma fase fundamental para o projeto de manipuladores paralelos. Esse processo de síntese consiste em uma abordagem sistemática, na qual um método é utilizado para gerar todas as possíveis estruturas mecânicas que sejam capazes de realizar um tipo de movimento. A Síntese do Tipo apresenta duas etapas principais: (1) Geração de pernas e (2) Montagem de manipuladores paralelos. A geração de pernas consiste em gerar cadeias cinemáticas que possuam tipos de movimentos de saída específicos. Essas cadeias cinemáticas são compostas por elos e juntas que apresentam configurações geométricas determinadas. Para a montagem dos manipuladores paralelos, as pernas geradas na primeira etapa são utilizadas. O movimento de saída que cada manipulador apresentará, ao final de sua montagem, dependerá do tipo de perna utilizado e do posicionamento de fixação das pernas. Neste trabalho será apresentada uma revisão dos principais métodos de síntese do tipo existentes, e as soluções de pernas geradas por cada método serão classificadas e organizadas utilizando uma única notação. Será apresentado também um novo método de síntese do tipo para a fase de geração de pernas. O algoritmo implementado para esse novo método combina características de algoritmos genéticos e teoria de helicoides. As soluções geradas pelo algoritmo foram comparadas com os resultados encontrados na literatura e, com isso, o método proposto foi validado

Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

Mobile parallel mechanisms (MPMs), which are parallel mechanisms with moveable bases, have previously been proposed to resolve the limited workspace of conventional parallel mechanisms. However, most previous studies on the subject focused on the kinematic analysis of some specific MPMs and did not discuss a type synthesis method for MPMs. With this in mind, we propose a screw theory-based type synthesis method to find out possible 6-degrees-of-freedom (DOF) MPM structures. In our proposed method, the 6-DOF mobility is divided into 3-DOF planar motion and 3-DOF spatial motion, both of which are realized by the transmitted planar motions of the driving units. Separately, the type synthesis of the entire MPM is divided into that of the driving unit and connecting chain. To realize 3-DOF spatial motion, two methods, applying singularity configuration and adding an additional chain, are proposed as ways to restrict undesired motions for the synthesis of the connecting chain. The driving unit is synthesized via the same type-synthesis method as the connecting chain by considering the driving unit as a planar mechanism. The method used to integrate the driving unit and the connecting chain was constructed based on whether the end pair of the connecting chain should be connected with the driving unit directly or driven by it through an actuating mechanism. As a result, 284 possible types of MPM structure are suggested and four examples of MPMs with six DOFs were synthesized to verify the feasibility of the proposed method

Rest-to-Rest Trajectory Planning for Underactuated Cable-Driven Parallel Robots

This article studies the trajectory planning for underactuated cable-driven parallel robots (CDPRs) in the case of rest-to-rest motions, when both the motion time and the path geometry are prescribed. For underactuated manipulators, it is possible to prescribe a control law only for a subset of the generalized coordinates of the system. However, if an arbitrary trajectory is prescribed for a suitable subset of these coordinates, the constraint deficiency on the end-effector leads to the impossibility of bringing the system at rest in a prescribed time. In addition, the behavior of the system may not be stable, that is, unbounded oscillatory motions of the end-effector may arise. In this article, we propose a novel trajectory-planning technique that allows the end effector to track a constrained geometric path in a specified time, and allows it to transition between stable static poses. The design of such a motion is based on the solution of a boundary value problem, aimed at a finding solution to the differential equations of motion with constraints on position and velocity at start and end times. To prove the effectiveness of such a method, the trajectory planning of a six-degrees-of-freedom spatial CDPR suspended by three cables is investigated. Trajectories of a reference point on the moving platform are designed so as to ensure that the assigned path is tracked accurately, and the system is brought to a static condition in a prescribed time. Experimental validation is presented and discussed

A Six-Dof Epicyclic-Parallel Manipulator

International audienceA new six-dof epicyclic-parallel manipulator with all actuators allocated on the ground is introduced. It is shown that the system has a considerably simple kinematics relationship, with the complete direct and inverse kinematics analysis provided. Further, the first and second links of each leg can be driven independently by two motors. The serial and parallel singularities of the system are determined, with an interesting feature of the system being that the parallel singularity is independent of the position of the end-effector. The workspace of the manipulator is also analyzed with future applications in haptics in mind

The Geometric Design of Spherical Mechanical Linkages with Differential Task Specifications: Experimental Set Up and Applications

The thesis focuses on the development of an experimental set up for a recently developed failure recovery technique of spatial robot manipulators. Assuming a general configuration of the spatial robot arm, a task is specified. This task contains constraints on position, velocity and acceleration to be satisfied. These constraints are derived from contact and curvature specifications. The technique synthesizes the serial chain and tests if the task can be satisfied in case of a joint failure. An experimental set up was developed in order to validate the failure recovery technique. It includes a robot arm mounted on a movable platform. The arm and platform are controlled by NI sbRIO board and are programmed in LabVIEW. The experimental results of the failure recovery technique were obtained for the case of Elbow failure in robot manipulators. The thesis considers two applications of the synthesis of spherical five –degree-of-freedom serial chains: Power assist for human therapeutic movement and Synthesis of Parallel Mechanical Linkages. A spherical TS chain has been synthesized for these two applications using the Mathematica software

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