Workspace Analysis and the Effect of Geometric Parameters for Parallel Mechanisms of the N-UU Class

N-UU class mechanisms, exemplified by the Omni-Wrist III, are compact parallel kinematic mechanisms (PKM) with large singularity free workspaces. These characteristics make them ideal for applications in robot wrists. This article presents the detailed kinematic and workspace analysis for four N-UU class mechanisms. More in detail, the equations defining the mechanism’s moving platform kinematics are derived as a function of the motion of the input links; these are then used to explore the mechanism’s workspace. These results are furthermore validated by comparing them to the results obtained from CAD-based simulations. The analyses suggests that the workspace of the mechanism is non-uniform, with a “warping” behaviour that occurs in an asymmetric fashion in a specific region of the workspace. Furthermore we show how the rotation of the input links, which mainly actuates the yaw and pitch angles of the mechanism, also causes unwanted coupled rotations along the roll axis.

A SYNTHESIS APPROACH FOR RECONFIGURABLE REDUNDANT PARALLEL KINEMATIC MECHANISMS

The design of a variety of novel Parallel Kinematic Mechanisms (PKMs) in the past three decades, and research into redundancy and reconfigurability have presented researchers with an opportunity to develop reconfigurable PKMs. In this paper, a novel synthesis approach for Reconfigurable Redundant PKMs (RR-PKMs) is presented. The approach, motivated by the required reconfigurability, can help synthesize RR-PKMs that reconfigure into lower mobility sub-configurations, assembly/working modes, and sub-PKMs, without the disassembly of the structure. Implementing the proposed approach for the design of a 5-dof machine tool, has led to the synthesis of a novel 3 × RRPRS based RR-PKM that can reconfigure into four PKMs.

Comparative Analysis of a Redundant Pentapod Parallel Kinematic Machine

Parallel kinematic mechanisms (PKMs) provide high stiffness and compact structures that are suitable for a large number of applications, including 5-axis milling. This paper presents a new pentapod-based PKM with an additional redundant degree-of-freedom (DOF) capable of reaching platform tilt angles of at least 90 deg over a large workspace. The proposed new PKM has a 6DOF 4 × SPRR + 1 × PSPR architecture. It is compared herein to Metrom® Pentapod as well as to several other pertinent PKMs in terms of workspace and dynamic stiffness. It is shown that the proposed mechanism can yield a tangibly larger workspace volume, when compared to those PKMs, while maintaining its high stiffness characteristics.

VIBRATION MODELING OF PARALLEL KINEMATIC MECHANISMS (PKMS) WITH FLEXIBLE LINKS: ADMISSIBLE SHAPE FUNCTIONS

The accuracy of various admissible shape functions, for vibration modeling of flexible links of Parallel Kinematic Mechanisms (PKMs), is investigated as a function of the ratio of the mass of the moving platform to the mass of the link. Knowing that the commonly used shape functions based on “pinned”, “fixed”, or “free” boundary conditions do not incorporate the moving platform mass, “pinned-mass” and “fixed-mass” shape functions are presented herein, and are compared with finite-element based results for various mass ratios. The closest shape functions to the finite-element results are, then, utilized and compared with other shape functions in the subsequent vibration modeling to predict the tooltip response.