A Bond Graph Based Modular Modeling Approach
towards an Automated Modeling Environment for
Reconfigurable Machine Tools
Tulga Ersal
Department of Mechanical Engineering
The University of Michigan
2350 Hayward St., Ann Arbor, MI 48109-2125, USA
Phone: +1-734-615-6567, E-mail: tersal@umich.edu
Jeffrey L. Stein
Department of Mechanical Engineering
The University of Michigan, Ann Arbor
Loucas S. Louca
Department of Mechanical and Manufacturing Engineering
University of Cyprus
Abstract - As is well known, due to their graphical and
acausal nature, bond graphs naturally lend themselves
to a modular approach to physical based modeling of
dynamic systems. In this paper we present a bond graph
based modular approach for modeling reconfigurable
machine tools (RMTs) as a multi-domain system. This
approach is the basis of an effort towards developing an
automated modeling environment for RMTs. The
mechanical components of an RMT system are treated
as three-dimensional rigid bodies that are connected
through joints, leading to a multibody representation of
the system. Non-mechanical components are also
considered and modeled through a modular approach.
The model of the system is obtained by assembling the
modular component models in a way that honors the
topology of the RMT. A modular model of an arch-type
reconfigurable machine tool system is developed to
illustrate the proposed methodology. The advantages
and disadvantages of the approach are discussed along
with the challenges that need to be addressed before an
automated modeling environment using this approach
can be implemented.
Keywords: bond graph, multibody system, reconfigurable
machine tool, modular modeling, hierarchical modeling
I. INTRODUCTION
A new generation of machine tools, called Reconfigurable
Machine Tools (RMTs), is being developed as part of an
effort to overcome the limitations and increase the
responsiveness of the current manufacturing systems
(Koren et al., 1999; Koren and Kota, 1999; Landers et al.,
2001). These machine tools are built with only the
manufacturing flexibility required by a given part family,
and through their modular structure, which allows the
reconfiguration of the machine tool, they provide the exact
functionality and capacity needed, exactly when needed.
This paper presents an ongoing effort on automating the
task of servo-axis modeling of a given RMT configuration.
The main purpose of having servo-axis models is to serve
the need to asses the effects of the servo-axis dynamics on
the accuracy of the machine tool. These models can assist
with the evaluation of the servo-axis performance of the
machine tool as well as with the design and control of the
servo-axes. What makes this problem more challenging is
that during the design process of an RMT numerous
configurations must be investigated and each configuration
requires its own model in order to assess the servo-axis
performance. Therefore, in order to make the RMT
modeling task less time demanding, less error-prone and
less challenging, it is desired to develop an automated
modeling environment.
The key idea of the approach presented in this paper is to
take advantage of the modular structure of the RMT and
map its modular structure into a modular modeling
environment. Having the modular models of the RMT
modules reduces the modeling task down to assembling the
modular models by just following the topology of the actual
modules in a given RMT configuration. In this paper, the
mechanical elements are emphasized and are treated as
three-dimensional rigid bodies in order to accommodate any
spatial motion that the machine modules may experience in
different configurations. This leads to a three-dimensional
multibody model representation for the RMT, where the
bodies, i.e. the modules, are interconnected through a
variety of three-dimensional joints.
Bond graphs are employed as the modeling tool for this
study for three main reasons: First, bond graphs are a
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