section. Particular attention is given to virtual assembly
because most of the researches related to the CAx-VR
integration have been done in this field. The rest of the
paper presents our studi es about the integration of VR
applications and CAx software. In parti cular in Sect. 3 we
describe the two interfaces developed for CAD-VR inte-
grations and in Sect. 4 the other interfaces related to the
CAE-VR integration.
2 Related works
The researches in the area of CAx-VR integration deal with
different topics, some of which are generic and regard the
generation of digital models dedicated to virtual prototyp-
ing, the others are strictly related to the specific application.
A typical problem that arises during the preparation of
digital models for VR applications regards the organisation
of the product data management (PDM) system. Inside the
PDM the components are organised in a typical tree structure
that is usually optimised for the development of classic
virtual verification like packaging, CAE, ergonomics, etc.
and not for verification through VR technologies. On this
topic Graf et al. [21] present a methodology and software
tool to automate the processing of data preparation for the
purposes of a design review session in VR. The proposed
system, named virtual design data preparation (VDDP), is
directly integrated with the PDM and allows the user to
navigate through the product structure, select entries for
conversion, correct geometric conversion errors and reduce
the complexity of the model. On the same topic Jayaram et
al. [22] present a method that improves the ability to use the
virtual assembly environment to simulate real world assem-
bly sequences in complex models, where there are significant
differences between the subassembly and hierarchy repre-
sentations in the CAD model and the component assembly
sequence in the factory floor.
Xu et al. [24] instead, propose a web-based virtual
environment that allows designers from different places and
with different software platforms to cooperate in the same
assembly scenario and to complete the assembly task
synchronously. The key technologies on which the system
is based are multimodal interaction and task processing.
Other typical problems in CAD-VR integration may
regard the loss of geome tric precision, topological infor-
mation, assembly structure and semantic data like dimen-
sions, names, constraints, physical properties, etc. [23]. In
order to achieve the VR interaction/visualisation, in fact, it
is necessary to have a manual reassignment of property,
wherever data are lost in the co nversion process. This
manual work represents a big inefficiency that is extremely
felt in the industrial world, because industries are progres-
sively reducing the product time to market.
2.1 Virtual assembly
Several virtual assembly (VA) applications are present in
literature. Among them Jayaram et al. [5, 6] describe a
feasibility study in using VR for design for assembly tasks
and some preliminary results from the use of a virtual
assembly application. During the assembly process the user
can store the path that was created or reject it and
reassemble the part. Collision detection methods warn the
user of interference and tolerance problems. A recent
research [7] proposes PLO-VATA (product lifecycle-orient-
ed virtual assembly technology architecture) in which VA is
adopted as an efficient, intuitive and convenient method for
assembly process modelling, simulation and analysis. In
this architecture, VA is decomposed into four basic
elements: principles and methodology of DFA, assembly
analysis and evaluation, virtual assembly model and virtual
assembly toolkits. In this way, immersion, concurrence,
integration and coll aboration are the four highlighted VA
main characteristics. Gomes de Sa and Zachmann [8] have
investigated the steps needed to apply VR for virtual
prototyping (VP) to verify assembly and maintenance
processes. They also report a user survey that has been
performed at BMW with a representative group of key
users. The response of the user survey was very encourag-
ing and optimistic. It seems that VR/VP does have the
potential to reduce the number of physical mock-ups and
improve overall product quality, especially in those parts of
the business process chain where human factors play an
important role.
Ye et al. [9] compare non-immersive and imme rsive
environments for assem bly planning. They present the
benefits of virtu al rea lity environments in supporting
assembly planning. Sun et al. [10] present real-time
planning in virtual environment using two-handed inter-
actions. Choi et al. [11] demonstrate an application of a
virtual assembly tool, named DYNAMO, for a grill plate
assembly.
Virtual assembly entails several topics concerning the
integration with CAD systems, most of them are related to
the loss of topological an d se mantic data during t he
conversion process from CAD to VR.
Jiang-sheng et al. [25
] have developed the data decom-
position and information translation method (DDITM) able
to export geometry, topology and assembly information
from the CAD system SolidWorks [20] into a virtual
assembly environment. Geometry information, generated
through the DTI (data translation interface), includes data
about the CAD surfaces and the tessellation. The surfaces
are treated as separated objects in these VR documents, so
the surface concept is constructed in VE by creating the
relations be tween surfaces and tessell ati ons. Topology
information of the CAD models is stored in a structure
Int J Adv Manuf Technol (2008) 38:1085–1097 1087