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Research Papers: Mechanisms and Robotics

Design and Prototyping of a New Balancing Mechanism for Spatial Parallel Manipulators

[+] Author and Article Information
C. Baradat

 Intelligent Surgical Instruments and Systems (ISIS), 20 Rue du Tour de l’Eau, F-38400 Saint Martin d’Hères, France; Département de Génie Mécanique et Automatique, LGCGM EA3913, Institut National des Sciences Appliquées (INSA), 20, Avenue des Buttes de Coësmes, CS 14315, F-35043 Rennes Cedex, France

V. Arakelian1

Département de Génie Mécanique et Automatique, LGCGM EA3913, Institut National des Sciences Appliquées (INSA), 20 Avenue des Buttes de Coësmes, CS 14315, F-35043 Rennes Cedex, Francevigen.arakelyan@insa-rennes.fr

S. Briot, S. Guegan

Département de Génie Mécanique et Automatique, LGCGM EA3913, Institut National des Sciences Appliquées (INSA), 20 Avenue des Buttes de Coësmes, CS 14315, F-35043 Rennes Cedex, France

It should be noted that in the balancing of high-speed mechanisms, the term “static balancing” refers to shaking force cancellation or minimization (1-2). With regard to the static balancing in robotics, this term differs from the first definition because in this case, the aim of the balancing is the minimization or cancellation of input torques of a mechanical system by means of gravitational force balancing.

1

Corresponding author.

J. Mech. Des 130(7), 072305 (May 22, 2008) (13 pages) doi:10.1115/1.2901057 History: Received February 15, 2007; Revised July 02, 2007; Published May 22, 2008

This paper proposes a new solution to the problem of torque minimization of spatial parallel manipulators. The suggested approach involves connecting a secondary mechanical system to the initial structure, which generates a vertical force applied to the manipulator platform. Two versions of the added force are considered: constant and variable. The conditions for optimization are formulated by the minimization of the root-mean-square values of the input torques. The positioning errors of the unbalanced and balanced parallel manipulators are provided. It is shown that the elastic deformations of the manipulator structure, which are due to the payload, change the altitude and the inclination of the platform. A significant reduction of these errors is achieved by using the balancing mechanism. The efficiency of the suggested solution is illustrated by numerical simulations and experimental verifications. The prototype of the suggested balancing mechanism for the Delta robot is also presented.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A Delta robot used in the SurgiScope®, a robotized navigation tool holder designed for neurosurgery and developed by the Intelligent Surgical Instruments and Systems (ISIS) company

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Figure 2

Principle of balancing

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Figure 3

Simplified scheme of the balancing mechanism

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Figure 4

Delta robot with the balancing mechanism

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Figure 5

Stewart platform with implemented balancing system

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Figure 6

Gravitational forces for leg i

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Figure 7

Input torque 1 for unbalanced (left) and balanced (right) Delta robots

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Figure 8

The output parameters for the selected trajectory

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Figure 9

Input torque 1 for unbalanced and balanced Delta robots

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Figure 10

Input torque 1 for unbalanced and balanced Delta robots

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Figure 11

Errors caused by the linear displacements and the rotation of the platform due to the elasticity of links for unbalanced (dark gray) and balanced (light gray) Delta robots calculated for the altitude z=−1m; (a) Errors caused by the linear displacements of the platform along the X axis; (b) errors caused by the linear displacements of the platform along the Y axis; (c) errors caused by the linear displacements of the platform along the Z axis; (d) errors caused by the rotation of the platform along the X axis; (e) errors caused by the rotation of the platform along the Y axis; (f) errors caused by the rotation of the platform along the Z axis

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Figure 12

Computer aided design model and prototype of the balancing mechanism implemented in the structure of the Delta robot

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Figure 13

Experimental bench

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Figure 14

Selected trajectory for experimental validation of torque minimization

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Figure 15

Experimental measures of input torques for three actuators of the Delta robot; (a) Input torque 1 (case E1); (b) input torque 2 (case E1); (c) input torque 3 (case E1); (d) input torque 1 (case E2); (e) input torque 2 (case E2); (f) input torque 3 (case E2)

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Figure 16

Measuring of the positioning errors for a given straight line trajectory

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Figure 17

Relative positioning errors with respect to the z axis for unbalanced and balanced robots

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