Real-Time Direct Position Analysis of Parallel Spherical Wrists by Using Extra Sensors

[+] Author and Article Information
R. Vertechy

DIEM,  University of Bologna, Viale Risorgimento, 2, 40136 Bologna, Italyrocco.vertechy@mail.ing.unibo.it

V. Parenti-Castelli

DIEM,  University of Bologna, Viale Risorgimento, 2, 40136 Bologna, Italyvincenzo.parenticastelli@mail.ing.unibo.it

J. Mech. Des 128(1), 288-294 (Apr 05, 2005) (7 pages) doi:10.1115/1.2114888 History: Received July 21, 2004; Revised April 05, 2005

The paper presents an algorithm for the real-time evaluation of the actual end-effector orientation of general parallel spherical wrists. Conceptually, the method relies on evidence that the pose of a rigid body is defined once the location of at least two linearly independent vectors attached to the body is known. The location of these vectors of the wrist end-effector is determined by the solution of the direct position analysis of some properly chosen kinematic chains (legs) of the manipulator. In order to accomplish this analysis, extra sensors, which measure suitable non-actuated variables of the chosen legs, need to be placed in addition to the ones normally embedded in the servomotors, i.e., the sensors which measure the actuated variables. From a mathematical point of view, the algorithm is built on the polar decomposition of a matrix and has inherent least square features. Thus, together with measurement redundancy, i.e., more sensors (extra sensors) than the mechanism degrees of freedom, the method also makes it possible to minimize the influence of both round-off and measurement errors on the estimation of the location of the wrist end-effector. The method is general but, in order to prove its effectiveness, without loss of generality it has been customized to the solution of the 3(UPS)-S fully parallel wrist architecture (where U, P and S are for universal, prismatic and spherical joint, respectively). Comparison of the proposed method, in both its general and specialized form, with others from the literature is provided.

Copyright © 2006 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

3(UPS)-S fully parallel spherical wrist

Grahic Jump Location
Figure 2

Orientation error: Method 1 vs Method 2

Grahic Jump Location
Figure 3

ith spherical-prismatic loop of the 3(UPS)-S

Grahic Jump Location
Figure 4

Orientation error: Method 1 vs Method 3




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