Traditional automatic assembly planningstudies the disassembly process based on
the assumption that “if you can disassemble a part, you
can assemble it, and vice versa.” In a real-world physical
situation, this may not be true due to irreversible fas-
tening processes. Also, for a given product, the number
of feasible assembly sequences explodes exponentially
as the number of components increases. In addition, the
optimal plan for disassembly may not represent the best
one for assembly. As Dewar et al.1 explain,
Attempts to accelerate the
process through the develop-
ment of computer-aided assem-
bly planning systems have not, in
general, been successful even
when the design has been carried
out using a modern CAD [com-
puter-aided design] system. One
of the main reasons for this lack
of success is that assembly is
dependent on a great deal of
expert knowledge that has
proven very difficult to formalize.
The development of virtual reality
(VR) applications in engineering has opened up an array
of tools to solve this problem. Instead of abstract algo-
rithmic assembly planning, an engineer can perform the
assembly intuitively in the virtual environment (VE)
using VR hardware and software. The information gen-
erated by this process can be used for assembly planning
and verification.
Virtual Assembly Design Environment (VADE)2,3
resulted from a research and development project start-
ed in 1995, sponsored by the National Institute of Stan-
dards and Technology (NIST). The main purpose of this
project was to explore the potential and the technical
challenges in using VR technologies for design and
manufacturing by creating a VE for assembly planning
and evaluation. Currently, we’re evaluating VADE using
test cases from industry.
In this article, we describe the overall system, the
important features, and examples of using VADE. We
also discuss the benefits and limitations of virtual assem-
bly systems. In addition, we compare virtual assembly
and automated assembly planning systems.
Assembly planning
Assembly planning for complex systems has always
been a difficult task for engineers. Although CAD sys-
tems allow configuration evaluation by letting engineers
visualize the final assembly, these systems don’t support
the visualization or planning of the assembly process.
Expert assemblers (in most cases still using the draw-
ing board) typically create process plans. Although
many systems (such as the one described by Kaufman
et al.4) are attempting to automate the planning process,
it’s very difficult to formalize the assembly planners’
knowledge. Moreover, assembly planning isn’t limited
to figuring out a set of feasible sequences of the parts.
Physical limitations of the workspace, tools, people, and
so on must be considered. Industry-accepted methods,
such as the system presented by Boothroyd and
Dewhurst,5 build on some of these factors (size, num-
ber of operations required, fasteners, and so on). This
system primarily targets cost analysis for the design and
not the assembly process planning. Thus, physical pro-
totypes (sometimes at a cost of several hundred thou-
sand dollars) are still the primary mode of evaluating
and planning the assembly process.
Related work
Several virtual assembly and virtual prototyping sys-
tems have been developed in the past.1,6-8 Some of these
systems6 interact with CAD systems. The system Ang-
ster6 described allows limited design modifications in
the VE through a CAD system (Pro/Engineer). However,
the level of interactivity limits the application. In Europe,
several activities in virtual prototyping and virtual assem-
0272-1716/99/$10.00 © 1999 IEEE
Virtual Reality
44 November/December 1999
The Virtual Assembly Design
Environment (VADE) is a
VR-based engineering
application that allows
engineers to plan, evaluate,
and verify the assembly of
mechanical systems.
Sankar Jayaram, Uma Jayaram, Yong Wang, and
Hrishikesh Tirumali
Washington State University
Kevin Lyons and Peter Hart
National Institute of Standards and Technology
VADE: A Virtual
Assembly Design
Environment