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Architecture Optimization of a 3-DOF Translational Parallel Mechanism for Machining Applications, the Orthoglide (0708.3381v1)

Published 24 Aug 2007 in cs.RO

Abstract: This paper addresses the architecture optimization of a 3-DOF translational parallel mechanism designed for machining applications. The design optimization is conducted on the basis of a prescribed Cartesian workspace with prescribed kinetostatic performances. The resulting machine, the Orthoglide, features three fixed parallel linear joints which are mounted orthogonally and a mobile platform which moves in the Cartesian x-y-z space with fixed orientation. The interesting features of the Orthoglide are a regular Cartesian workspace shape, uniform performances in all directions and good compactness. A small-scale prototype of the Orthoglide under development is presented at the end of this paper.

Citations (321)

Summary

  • The paper demonstrates the optimization of the Orthoglide, merging serial precision with the structural advantages of parallel kinematics.
  • The design employs Jacobian conditioning and manipulability ellipsoid constraints to ensure isotropic performance within a cube-like workspace.
  • The prototype validates a singularity- and collision-free mechanism, opening avenues for dynamic control and broader machining applications.

Architecture Optimization of a 3-DOF Translational Parallel Mechanism for Machining Applications: The Orthoglide

The paper presents a meticulous paper and architectural optimization of a 3-DOF translational parallel mechanism named the Orthoglide. This mechanism has been tailored specifically for machining applications. The primary design objective is achieving a mechanism that melds the chief advantages of serial machine tools, such as uniform and predictable performance across the workspace, with the intrinsic benefits of parallel kinematic machines (PKM), which include high structural rigidity and dynamic capacity.

Design and Optimization Approach

The design optimization is founded upon key constraints within the Cartesian workspace, aiming for uniform kinetostatic performances across the entire workspace. This approach leads to the development of the Orthoglide, characterized by its regular parallelepiped workspace shape, consistent performance metrics in all major directions, and a compact form factor. The design considerations initiated from a Delta-type architecture and were fine-tuned through an optimization procedure. Two primary criteria shaped the optimization: the conditioning of the Jacobian matrix and the manipulability ellipsoid.

The conditioning of the Jacobian matrix ensures an isotropic architecture where tool forces and velocities are equalized in all directions. The manipulability ellipsoid offers further constraints that define joint limits and link lengths concerning a desired Cartesian workspace size and specified transmission factor limits.

Mechanism Details

The novel architecture features three fixed linear joints and three articulated parallelograms. The design mandates that the parallel singularities occur when certain conditions involving linear dependence of vectors are met. These singularities, along with serial singularities where the determinant of the serial Jacobian matrix vanishes, are kept away from the designated workspace through careful optimization.

For the Orthoglide, a particular isotropic condition is achieved when the linear joints are arranged orthogonally. This unique isotropic configuration aligns the Cartesian workspace to approximate a cube, thereby ensuring the organization retains simplicity and avoids undesirable singularities.

Implications and Future Developments

The work on the Orthoglide showcases a mechanism that meets regular machining requirements with a predictable and consistent workspace, which is crucial for applications demanding high precision across varying paths. The Orthoglide achieves significant progress by offering transmission factors akin to those of a serial machine tool while embedding the beneficial structural characteristics of PKM.

The optimization process yields a workspace free of singularities and self-collisions, and the prototype’s successful construction verifies the feasibility of the proposed design. Future directions could explore dynamic control implementations and expanded material applications, which the authors suggest they are currently investigating with finite element analyses.

In conclusion, the Orthoglide mechanism introduces a significant contribution towards bridging the gap between serial and parallel kinematic machine tools, offering a promising avenue for further research and development in rapid machining applications. The systematic design procedure presents a replicable methodology that could be adapted to future innovations in the field of robotic machining.