A generalized approach for computing the transmission index of parallel mechanisms

This paper presents a novel approach for computing the transmission index of parallel mechanisms. The approach is based on an extended concept to compute the maximal virtual coefficient, which is an important notion involved in the formulation of dimensionally homogeneous transmission indices for singularity analysis and dimensional optimization of parallel mechanisms. By exploiting the dual property of the virtual coefficient, two characteristic points instead of one as in the current state of the art are defined: one characteristic point – termed the transmission characteristic point – is located on the ‘floating’ axis of the transmission wrench, as in existing approaches, while a second one – termed the output characteristic point – is located on the floating axis of the output twist of the platform, which is a novel concept. This allows one to define two characteristic lengths, namely, the transmission and output characteristic lengths, respectively, of which the larger is then used for the measure of the “distance” between the transmission wrench screw and the output twist screw. As shown in this paper, this new measure makes it possible to discern more finely the configuration-dependent properties of kinematic performance of parallel mechanisms, thus making it more suitable for dimensional optimization. Confidence in this statement is demonstrated through the comparative study of two in-parallel mechanisms using the new method and previously existing ones

Improvement of Functional Performance of Spatial Parallel Manipulators Using Mechanisms of Variable Structure

International audienceA procedure for the increase of singularity-free zones in the workspace of spatial parallel manipulators is presented in this paper. The procedure is based on the control of the pressure angles in the joints of the manipulator. The zones, which cannot be reached by the manipulator, are detected. For increase of the reachable workspace of the manipulator the legs of variable structure are proposed. The design of the optimal structure of the spatial parallel manipulator 3-RPS is illustrated by a numerical simulation

A simple and visually orientated approach for type synthesis of overconstrained 1T2R parallel mechanisms

This paper presents a simple and highly visual approach for the type synthesis of a family of overconstrained parallel mechanisms that have one translational and two rotational movement capabilities. It considers, especially, mechanisms offering the accuracy and dynamic response needed for machining applications. This family features a spatial limb plus a member of a class of planar symmetrical linkages, the latter connected by a revolute joint either to the machine frame at its base link or to the platform at its output link. Criteria for selecting suitable structures from among numerous candidates are proposed by considering the realistic practical requirements for reconfigurability, movement capability, rational component design and so on. It concludes that a few can simultaneously fulfil the proposed criteria, even though a variety of structures have been presented in the literature. Exploitation of the proposed structures and evaluation criteria then leads to a novel five degrees of freedom hybrid module named TriMule. A significant potential advantage of the TriMule over the Tricept arises because all the joints connecting the base link and the machine frame can be integrated into one single, compact part, leading to a lightweight, cost effective and flexible design particularly suitable for configuring various robotized manufacturing cells

Static and dynamic performance evaluation of a 3-DOF spindle head using CAD–CAE integration methodology

Accurate and rapid modeling and performance evaluation over the entire workspace is a crucially important issue in the design optimization of parallel kinematic machines (PKMs), especially for those dedicated for high-speed machining where high rigidity and high dynamics are the essential requirements. By taking a 3-DOF spindle head named A3 head as an example, this paper presents a feature-based CAD–CAE integration methodology for the static and dynamic analyses of PKMs. The approach can be implemented by four steps: (1) creation of a parameterized geometric (CAD) model with analysis features in SolidWorks; (2) extraction of the features from the CAD model using the Application Programming Interface (API) available in SolidWorks; (3) formulation of a CAD model in SAMCEF by mapping the configuration features from SolidWorks to SAMCEF; and (4) conversion of the analysis features into a scripting language named Bacon for Finite Element Analysis (FEA). The merit of this approach lies in that the FE model at different configurations can be updated automatically in batch mode, and PKMs having different topologies can be modeled with ease thanks to the down to link/joint level featuring. The experiment is also carried out to verify the effectiveness of the proposed approach

Elastokinetics modeling and characteristic analysis of the parallel robot mechanism

This paper focuses a new 4-UPS-RPS five degree of freedom (DOF) spatial parallel robot mechanism with independent intellectual property rights obtained. Based on KED method and together with finite element method, Lagrange equation and substructure modeling method, the elastokinetics analytical model of this parallel robot mechanism is established under the ideal situation. Subsequently, the research results, such as elastokinetics model, stress and frequency characteristic analysis, are obtained. Combined with typical examples, key design parameters which significantly influence the dynamic characteristics of the system, are explicated. The work done in this paper lays a solid foundation for the dynamic optimum design of parallel robot mechanism and the physical prototype development

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

Kinematic calibration of a 3-DOF spindle head using a double ball bar

This paper presents a simple and effective approach for kinematic calibration of a 3-DOF spindle head developed for high-speed machining. This approach is implemented in three steps, (i) error modeling that allows the geometric errors affecting the compensatable and uncompensatable pose accuracy to be classified; (ii) identification of the geometric errors using a set of distance measurements acquired by a double ball bar (DBB) with a single installation; (iii) design of a linearized error compensator for real-time error implementation. Experimental results on a prototype machine show that the compensatable pose accuracy can significantly be improved by the proposed approach

Mechatronic development and dynamic control of a 3-DOF parallel manipulator

This is an Author's Accepted Manuscript of an article published in Mechanics Based Design of Structures and Machines: An International Journal, 40:4, 434-452 [September 2012] [copyright Taylor & Francis], available online at: http://www.tandfonline.com/10.1080/15397734.2012.687292The aim of this article is to develop, from the mechatronic point of view, a low-cost parallel manipulator (PM) with 3-degrees of freedom (DOF). The robot has to be able to generate and control one translational motion (heave) and two rotary motions (rolling and pitching). Applications for this kind of parallel manipulator can be found at least in driving-motion simulation and in the biomechanical field. An open control architecture has been developed for this manipulator, which allows implementing and testing different dynamic control schemes for a PM with 3-DOF. Thus, the robot developed can be used as a test bench where control schemes can be tested. In this article, several control schemes are proposed and the tracking control responses are compared. The schemes considered are based on passivity-based control and inverse dynamic control. The control algorithm considers point-to-point control or tracking control. When the controller considers the system dynamics, an identified model has been used. The control schemes have been tested on a virtual robot and on the actual prototype. © 2012 Taylor & Francis Group, LLC.The authors wish to express their gratitude to the Plan Nacional de I+D, Comision Interministerial de Ciencia y Tecnologia (FEDER-CICYT) for the partial financing of this study under the projects DPI2009-13830-C02-01 and DPI2010-20814-C02-(01, 02). This work was also supported in part by the CDCHT-ULA Grant I-1286-11-02-B.Vallés Miquel, M.; Díaz-Rodríguez, M.; Valera Fernández, Á.; Mata Amela, V.; Page Del Pozo, AF. (2012). Mechatronic development and dynamic control of a 3-DOF parallel manipulator. 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