Modelling analysis and synthesis of 3-DOF parallel manipulators

Abstract

Parallel manipulators (PMs) have been the subject of study, of much robotic research during the past three decades. A parallel manipulator (PM) is a closed loop kinematic chain mechanism, that is connected to the base via multiple independent chains. Parallel manipulators can provide several advantages over serial manipulators in terms of low inertia, high stiffness, high rigidity and accuracy. These advantages arise due to the presence of kinematic loops within the manipulator, that allow the load to be transmitted to the ground via multiple chains. However, these kinematic closed loops cause the workspace of the parallel manipulators to be severely limited. Apart from the workspace, parallel manipulators also have some disadvantages such as their complicated structure, high cost and major challenge for their analysis and control. To overcome the above disadvantages, the development of parallel manipulators less than 6-DOF has been accelerated. However, the analysis of the PM is complicated, because of the constraints and various singularities. As a result, PMs are not as popular as serial manipulators, because of lower mobility, workspace and complex structure. The scope of this research work is to perform the modelling, simulation, dimensional synthesis and the kinematic, work volume and singularity position analyses of the three degrees of freedom PMs (TRIPOD and TRI-GLIDE). Since the mobility and workspace are quite complex in PM design, the models were fabricated by considering those conditions, and the fabricated models were modeled and simulated using the ADAMS software package. In this work the following manipulators were modeled, simulated and fabricated. They are (1) 3-DOF (Prismatic-Revolute-Spherical) Tri-Glide manipulator with rigid links (actuating screws kept in a horizontal position), (2) 3-DOF (Prismatic-Revolute-Spherical) Tripod manipulator with rigid links (actuating screws kept in a vertical position), (3) 3-DOF (Prismatic- Revolute-Revolute) PM