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

Self-Motions of General 3-RPR Planar Parallel Robots

This paper studies the kinematic geometry of general 3-RPR planar parallel robots with actuated base joints. These robots, while largely overlooked, have simple direct kinematics and large singularity-free workspace. Furthermore, their kinematic geometry is the same as that of a newly developed parallel robot with SCARA-type motions. Starting from the direct and inverse kinematic model, the expressions for the singularity loci of 3-RPR planar parallel robots are determined. Then, the global behaviour at all singularities is geometrically described by studying the degeneracy of the direct kinematic model. Special cases of self-motions are then examined and the degree of freedom gained in such special configurations is kinematically interpreted. Finally, a practical example is discussed and experimental validations performed on an actual robot prototype are presented

Profile Synthesis Of Planar Variable Joints

Reconfigurable mechanisms provide quick changeover and reduced costs for low volume manufacturing applications. In addition, these mechanisms provide added flexibility in the context of a constrained environment. A subset of planar reconfigurable mechanisms use variable joints to provide this added adaptability. In this dissertation, the profile synthesis of planar variable joints that change from a rotational motion to a translational motion was investigated. A method was developed to perform automated profile synthesis. It was shown that combinations of higher variable joints can be used to create kinematically equivalent variable joints that are geometrically different. The results were used to create two new reconfigurable mechanisms that utilize the synthesized variable joints. The first reconfigurable mechanism is a four-bar mechanism that performs a rigid body guidance task not possible using conventional four-bar theory. The second mechanism uses variable joints in a 3-RPR parallel mechanism for singularity avoidance without adding redundant actuation

Kinematics, workspace and singularity analysis of a multi-mode parallel robot

A family of reconfigurable parallel robots can change motion modes by passing through constraint singularities by locking and releasing some passive joints of the robot. This paper is about the kinematics, the workspace and singularity analysis of a 3-PRPiR parallel robot involving lockable Pi and R (revolute) joints. Here a Pi joint may act as a 1-DOF planar parallelogram if its lock-able P (prismatic) joint is locked or a 2-DOF RR serial chain if its lockable P joint is released. The operation modes of the robot include a 3T operation modes to three 2T1R operation modes with two different directions of the rotation axis of the moving platform. The inverse kinematics and forward kinematics of the robot in each operation modes are dealt with in detail. The workspace analysis of the robot allow us to know the regions of the workspace that the robot can reach in each operation mode. A prototype built at Heriot-Watt University is used to illustrate the results of this work.Comment: International Design Engineering Technical Conferences \& Computers and Information in Engineering Conference, Aug 2017, Cleveland, United States. 201

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

Self Motions of the Pantopteron

International audienceIn this paper, the self motions of a novel 3-DOF fully de-coupled translational parallel robot, called the Pantopteron, are presented. The Pantopteron is similar to the well-known Car-tesian parallel manipulator (Tripteron), but due to the use of pantograph linkages, an amplification effect is achieved. Therefore, equipped with the same actuators, the mobile platform of the Pantopteron moves faster than that of the Trip-teron. This amplification is defined by the magnification factor of the pantograph linkages. The self motions are probably the most critical types of singularities a manipulator can meet. Therefore it is of utmost importance to have a good knowledge of them. Design considerations are also discussed in order to create Pantopterons without self motions

Pantopteron-4: a New 3T1R Decoupled Parallel Manipulator for Pick-and-Place Applications

International audienceIn this paper, a novel 4-DOF decoupled parallel manipulator with Schoenflies motions, called the Pantopteron-4, is presented. This manipulator is able to perform the same movements as the Isoglide4 or the Quadrupteron, but, due to its architecture which is made of three pantograph linkages, an amplification of the movements between the actuators and the platform displacements is achieved. Therefore, having the same actuators for both robots, the Pantopteron-4 displaces (theoretically) many-times faster than the Isoglide4 or the Quadrupteron, depending on the magnification factor of the pantograph linkages. Thus, this mechanism is foreseen to be used in applications where the velocities and accelerations have to be high, as in pick-and-place. First, the kinematics of the Pantopteron-4 is presented. Then, its workspace is analyzed. Finally, a prototype of the mechanism is shown and conclusions are given