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Workspace Limiting Strategy for 6 DOF Force Controlled PKMs Manipulating High Inertia Objects

Department of Mechanical Engineering, Politecnico di Milano, 20156 Milano, Italy
Dipartimento di Ingegneria Industriale e dell’Informazione, Università degli Studi di Pavia, Via A.Ferrata 5, 27100 Pavia, Italy
Authors to whom correspondence should be addressed.
Robotics 2018, 7(1), 10;
Received: 8 December 2017 / Revised: 31 January 2018 / Accepted: 31 January 2018 / Published: 5 February 2018
PDF [4812 KB, uploaded 6 February 2018]


This article describes an efficient and effective strategy for limiting the workspace of a six degrees of freedom parallel manipulator, with challenging motion smoothness requirements due to both the high inertia objects carried by the end effector and the pose references coming from a force feedback loop. Firstly, a suitable formulation of the workspace is studied, distinguishing between different conventions and procedures. Thereafter a discrete and analytical formulation of the workspace is obtained and developed in order to suit this application. Having obtained the limits, a methodology to evaluate the robot pose is discussed, taking into account the reference pose buffering technique and the real time pose estimation through the numeric solution of the nonlinear forward kinematics equations. The safety algorithm designed checks the actual robot pose and future poses to be commanded, and takes control of the reference pose generation process, if an exit of the safety workspace is detected. The result obtained is a soft compliant surface within which the robot is free to move, but outside of which a “force field” pushes the robot end-effector to return smoothly. To reach this objective, the control deflects the end effector trajectory safely and smoothly and moves it back to within the workspace limits. Nevertheless, this preserves the continuity of the velocity and controls the acceleration, to avoid dangerous vibrations and shocks. Simulation and experimental result tests are conducted to verify the algorithm effectiveness and the efficient implementation. View Full-Text
Keywords: workspace boundaries; parallel kinematic manipulator; hardware in the loop workspace boundaries; parallel kinematic manipulator; hardware in the loop

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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La Mura, F.; Romanó, P.; Fiore, E.; Giberti, H. Workspace Limiting Strategy for 6 DOF Force Controlled PKMs Manipulating High Inertia Objects. Robotics 2018, 7, 10.

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