Constraint Wrench Formulation for Closed-Loop Systems Using Two-Level Recursions

[+] Author and Article Information
Himanshu Chaudhary

 M.L.V. Textile and Engineering College Bhilwara, Pratap Nagar, Bhilwara (Rajasthan) 311001, Indiahimanshubhl@rediffmail.com

Subir Kumar Saha

Department of Mechanical Engineering, I.I.T. Delhi, Hauz Khas, New Delhi 110016, Indiasaha@mech.iitd.ernet.in

Note that n-vector represents n dimensional vector.

J. Mech. Des 129(12), 1234-1242 (Jan 12, 2007) (9 pages) doi:10.1115/1.2779890 History: Received August 22, 2006; Revised January 12, 2007

In order to compute the constraint moments and forces, together referred here as wrenches, in closed-loop mechanical systems, it is necessary to formulate a dynamics problem in a suitable manner so that the wrenches can be computed efficiently. A new constraint wrench formulation for closed-loop systems is presented in this paper using two-level recursions, namely, subsystem level and body level. A subsystem is referred here as the serial- or tree-type branches of a spanning tree obtained by cutting the appropriate joints of the closed loops of the system at hand. For each subsystem, unconstrained Newton–Euler equations of motion are systematically reduced to a minimal set in terms of the Lagrange multipliers representing the constraint wrenches at the cut joints and the driving torques/forces provided by the actuators. The set of unknown Lagrange multipliers and the driving torques/forces associated to all subsystems are solved in a recursive fashion using the concepts of a determinate subsystem. Next, the constraint forces and moments at the uncut joints of each subsystem are calculated recursively from one body to another. Effectiveness of the proposed algorithm is illustrated using a multiloop planar carpet scraping machine and the spatial RSSR (where R and S stand for revolute and spherical, respectively) mechanism.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 7

Subsystems of spanning tree for the carpet scraping mechanism

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Figure 8

Comparison of driving torque

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Figure 1

Closed loops of a multiloop system: (a) the closed loops and (b) its open loops

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Figure 3

Open systems for four-bar mechanism

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Figure 5

Constraint wrenches calculation using two-level recursive subsystem approach

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Figure 6

Carpet scraping mechanism

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Figure 9

The RSSR mechanism

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Figure 10

Spanning tree of the 7R mechanism



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