Designing cable harness assemblies in virtual environments
Post on 14-Jul-2016
Designing cable harness assemblies in virtual environments
F.M. Ng, J.M. Ritchie*, J.E.L. Simmons, R.G. DewarDepartment of Mechanical and Chemical Engineering, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK
Cable harness assemblies are amongst the most costly items in any electro-mechanical product. The domain is not widely recognised as
an area for academic research. Internationally, some efforts have been made to automate or semi-automate the choice of cable harness path
through the use of artificial intelligence (AI) via CAD systems, but with little success. Common themes voiced are that the problem is too
open-ended and it is very difficult to capture the design intent of the activity. Human input is still very much required to guide the computer
systems to reach an optimum solution. Case study investigations were carried out at five advanced manufacturing organisations to
determine the current industrial practice. The investigations revealed that the cable harness design and planning (CHDP) process is
essentially sequential in nature and consists of lengthy activities carried out late in the overall product development cycle. It was also found
that there has been little attempt to integrate any of the core activities involved. This paper describes work undertaken at Heriot-Watt
University to research the effectiveness of immersive virtual reality for designing and routing cable harnesses by enhancing the expertise of
the cable harness designer rather than by replacing the individual via an automated system. The new virtual cable design system developed
in the course of this work has now undergone some pilot trials to test its usability. The system will subsequently be used to carry out full
industrial trials in conjunction with a number of high technology equipment manufacturers. These pilot trials, combined with the case
studies of current practice carried out at the companies, have highlighted a number of issues regarding cable design, particularly that
immersive VR has a potentially unique role to play in the integration of cable harness electrical and mechanical design activities.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Immersive virtual reality; Cable harness design
Cable harnesses are a vital part of all electro-mechanical
systems from aircraft and automobiles to personal compu-
ters and domestic appliances. In many instances the cable
harness is one of the most costly items in the overall
engineered system. In spite of this the detail design and
planning of cable harnesses are often only addressed almost
as afterthoughts at the end of the product design process.
Cable harness design and planning (CHDP) in fact cover a
set of manually intensive, time-consuming and costly activi-
ties. There is the obvious problem of determining satisfac-
tory routes for bundles of cables in crowded spaces. The
wires themselves will vary in size depending on their duties.
The stiffness and mass distribution of the bundle is deter-
mined by the size and type of cables involved. Acceptable
bend radii must be defined as well as the position and
distribution of the fasteners used to constrain the harness.
One important concern for harness designers is that of
voltage drop. Voltage drop is directly proportional to cable
length and inversely proportional to cable cross-sectional
area. Ideally, the designer must find a routing configuration
that maintains a suitable voltage drop for all cables in the
bundled harness. Fig. 1 shows an example of a completed
cable harness ready for assembly into a final product.
Current industrial practice, confirmed in case study inves-
tigations at five leading UK companies, often requires the
building of a physical prototype of a new design before
engineers are able to manually determine the correct cable
lengths and routes, as well as the numbers and positions of
fasteners. Once a set of suitable cable paths have been
chosen and the associated components selected, the results
are entered into a database that allows the production of two-
dimensional drawings and parts lists together with assembly
instructions. It is vital that this information is accurate and
well-proven since the actual manufacture of the harness
assembly is often carried out by an external specialist
The routing problem is further complicated by the vulne-
rability of the cable harness to decisions made upstream. The
cable harness may have to be reconfigured after only minor
changes that affect, say, the chassis and the individual
modules within a prototype product. The routing process
Journal of Materials Processing Technology 107 (2000) 3743
* Corresponding author.
E-mail address: firstname.lastname@example.org (J.M. Ritchie).
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can even result in the late and expensive re-design of the
machine chassis to allow the cables to reach their terminal
In spite of its industrial importance, cable harness design
is not widely recognised as an area for academic research.
Most investigators who have explored the subject have
attempted to semi-automate or automate the choice of
harness path through the use of artificial intelligence (AI)
in conjunction with CAD systems. Such systems are used as
a review tool for use after the equipment has been designed.
Park et al.  recognised that cable harness design
requires in depth three-dimensional spatial reasoning. They
proposed the use of agents to produce different cable
configurations that satisfy the pin-to-pin connections of a
typical harness circuit layout and automate routine opera-
tions such as moving a section of bundles from one position
to another. Conru and Cutkosky [2,3] report that they have
incorporated into Park et al.s system a set of algorithms that
attempt to automate cable routing in a 3D environment. Two
genetic algorithms were developed to route cable harnesses
in a 3D environment. Finally, Petrie et al.  report the
development of a harness design system called Next-Link
that allows different designers to create different harness
layout concurrently. Next-Link is essentially a manage-
ment tool that uses a software agent to co-ordinate, update
and keep track of the work of individual designers, evaluat-
ing all the routings developed by each designer based on
satisfying global constraints.
Much more recently, Cerezuela et al.  carried out a case
study on cable harness design at a helicopter manufacturing
company. From the case study they found that harness
design is an iterative process involving schematic, routing
and component design. It is postulated that harness design is
a dynamic process and it is not feasible to automate the
entire activity by computers. Thus, Cerezuela et al. propose
a conceptual knowledge based decision support system to
assist in the design of cable harnesses.
In summary, the review of published academic literature
in the design and planning of cable harnesses shows that
much of the limited amount of research in the area has been
concerned with developing automated or semi-automated
systems for determining cable routings. The algorithms
developed tend to be demonstrated in simple geometric
layouts of components and little evidence is provided that
the work has been applied in industry.
3. Industrial case studies
As part of the present research, case study investigations
were carried out carried out at five UK advanced electro-
mechanical technology businesses. These were carried
through extensive visits, discussions and meetings with
practitioners and managers. The results were documented
and returned to the companies involved for their verification.
Taken together, the five case studies show that the CHDP
process is essentially sequential in nature and consists of
lengthy activities carried out late in the overall product
development cycle. The investigations revealed that there
has been little attempt to integrate any of the core activities
involved. It was also found that companies are increasingly
using CAD based systems to support the design of harnesses.
There was also no evidence to suggest the use of automated
or semi-automated harness design tools in use by the
companies, confirming prior impressions obtained from
the literature survey.
The case studies results were used to create a generic
model shown by Fig. 2 for the CHDP process; this provides
Fig. 1. Complete cable harness prior to assembly.
Fig. 2. General stages in the harness design and planning process.
38 F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743
an outline picture of how manufacturing companies in the
electro-mechanical sector address the cable harness design
problem. The model is of course subject to detail change in
particular cases dependent on the types of product manu-
factured and the required electrical specifications.
The contention of the work described in this paper is that
companies prefer to have cable harness design as an inter-
active technique under the control of the designer. The
remaining sections of the paper describe a prototype immer-
sive virtual reality demonstrator system, developed to assist
designers in producing feasible virtual prototype harness
assemblies, and the corresponding pilot trial results.
4. Cable layout using immersive virtual reality
The virtual design and planning cable routing system at
Heriot-Watt University is implemented on a Hewlett-Pack-
ard workstation with additional VR hardware and software
from Division Ltd. CAD models of a prototype assembly can
be imported directly into the system which negates the need
for any extra component modelling. As illustrated in Fig. 3,
the user interacts with the system by means of a head
mounted display (HMD). This provides a stereo image of
the virtual environment. A three-dimensional mouse (3D) is
used as an input device.
The ability to touch and feel objects in the real world is
one that is taken for granted. However, the development of
viable systems to provide this haptic feedback in virtual
environments is still the subject of much research . For
this reason, the system described here makes use of alter-
native visual and audio cues to highlight collisions. A full
polygonal collision detection algorithm is available in the
software. Thus, when a collision occurs, the system utilises
messages sent from the algorithm to make images of objects
in the virtual world turn to wire-frame representations. This,
along with a simple audio cue, informs the user that some-
thing is amiss (Fig. 4).
The virtual cable router has five key design tools in its
operation namely, point-to-point, continuous path,
way-point routing, rubber banding and size manage-
ment. Collision detection is inherent within the first three
features. Point-to-point and continuous path are creation
functions, whereas way-point routing allows the creation of
cable bundle assemblies along existing routes. Rubber
banding is normally used during editing and size manage-
ment enables the user to amend the size of the model relative
to the system user. All the features are activated through a
virtual toolbox as shown in Fig. 5.
The point-to-point technique of routing cables provides
the capability to generate outline cable routes rapidly by
picking positions or nodes in the virtual environment. The
user simply probes ports located on cable connectors, or a
point in space, and a section of cable appears between this
and the last node created as shown in Fig. 6. Once an existing
node has been picked in an operation it can be moved around
in three dimensions, stretching or contracting the associated
cables as required. This editing facility within point-to-point
is called rubber banding and is described later. The picking
Fig. 3. A user interacting in the virtual environment.
Fig. 4. Wire-frame collision warning of a clash with a cable.
Fig. 5. A virtual toolbox.
F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743 39
of another node makes that node active and any subsequent
point chosen in space will create a section of cable
between it and the active node. By choosing existing nodes,
multiple spliced or breakaway cable branches can emanate
from a single node. Some examples of these are shown in
4.2. Continuous path
Continuous path generates a cable route by extruding a
new section from a user-selected node. Thus, by picking an
existing node, or a port on a connector, a new node is created
and attached to the virtual hand until the node is released.
This method has rubber banding implicit within it also; the
new section changes in length and position as the virtual
hand moves. In a fashion similar to point-to-point, multiple
spliced or breakaway cable branches can be produced.
The user can observe collisions and immediately take
action to move the section and so as to avoid a clash. Again,
this method allows for creating nodes with multiple
4.3. Way-point routing
Having laid one cable, it is possible quickly to lay bundles
of cables along the same route by using way-points. This is
achieved by simply choosing the relevant beginning and end
nodes along the common length of an existing cable between
which a new cable is to run.
4.4. Rubber banding
Once the entire cable layout is produced some modifica-
tions may be required. The rubber banding facility allows
the user to re-position either entire sections of cable or
bundles that are knitted together simply by holding on to and
subsequently moving a node. Although this editing facility
stands alone, it has already been mentioned that it is avail-
able in the point-to-point and, to some extent, the continuous
4.5. Size management
The final VR cable layout tool developed and defined as
part of this research is size management. This provides the
user with the ability to enlarge or shrink the virtual prototype
to enable human-scale ergonomic access to either fine
geometry details or large-scale geometric features within
the virtual environment as well as deal with any scale of
5. System architecture
The set of nodes and cable sections created by the user are
stored in a multi-linked graph structure containing a linked
list of nodes and a further linked list of joins for each node
 (Fig. 8).
At the end of the routing session, the system generates a
text file by traversing the graph structure and extracting
useful information which details the bills-of-materials and
process planning information associated with the physical
cable harness. These outputs include the types of end
connectors and cable configurations selected as well as
the positions and liaisons that exist between the virtual
nodes as shown in Fig. 8. The connector type and liai-
sons/cable configurations indicated in the text file are spe-
cified by the user during the immersive routing session. The
numbers highlighted on the connector type list describe the
physical configuration of the connector, i.e. actual size,
number of crimps found on the connector. The liaisons/
cable configurations, on the other hand, describe the types of
bundles of wires that are specified for use within certain
sections of the cable harness layout. A post-processor has
been developed to convert the data within the text file into a
two-dimensional layout of the cable harness in AutoCAD
DXF format. This drawing can be used in the manufacture of
the physical cable harness.
Fig. 6. Cables leaving a connector via ports.
Fig. 7. A cable harness laid out on an assembly in the virtual world.
40 F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743
6. Pilot study
A pilot study was carried out to evaluate:
1. the usability and robustness of the VR routing tools
2. the effects of learning by comparing repetitions for each
methods and the key differences between the two cable
Six participants took part in the pilot study, aged between
23 and 30, all were male post-graduate students from the
Department of Mechanical and Chemical Engineering at
Heriot-Watt University. None of them had used an immer-
sive virtual reality system before. A description of the
experiment and the results now follows.
6.1. Experimental procedure
The participants task was to produce a cable route from
one side of the wall of a virtual component to the other side
while immersed in the virtual environment as shown in
Figs. 9 and 10. They were asked to develop a route by
following the contours of the component. The six partici-
pants were divided into two groups of three denoted as PTP
and CP group. The first group used point-to-point and the
other group used continuous path to develop the cable paths.
Each participant performed the task for 10 consecutive trials
and the time to complete the task was measured for each one.
In order to detect improvement in performance for all
trials, one-way analysis of variance (ANOVA) was carried
out for both PTP and CP participants. The one-way ANOVA
tests were applied to the task completion time (TCT) scores
of both groups. The TCT defines the total time required for
completing a trial in an experiment. The analysis revealed
significant differences between the trials within the PTP
group based on the scores, F9; 20 7:19; p 0:0001,suggesting that there is overall improvement in performance
between the trials. Statistical differences were not detected
between the trials for the CP group, F9; 20 0:89; p 0:55, confirming that the CP method of routing cable path ismuch more difficult to learn.
Subsequently, student t-tests were applied to identify
improvement in performance from the later trials when
compared with trial 1 for scores from TCTs both PTP
and CP groups. The results from the t-tests on TCT data
are tabulated in Tables 1 and 2. The t-tests revealed sig-
nificant differences within the PTP group for trials 35, 710
Fig. 8. An example of the output from the system.
Fig. 9. Layout of the assembly. Fig. 10. An example of a laid cable in place for the experiment.
F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743 41
when compared with trial 1, suggesting that participants
were learning quickly. On the other hand, no significant
differences were detected between trial 2 and 6 when
compared with trial 1. The trial 2 finding indicates
that participants are still learning to use the method.
From the video recordings, it was found that participants
tend to explore alternative routes in trial 6, thus statistical
significance was not detected as participants were spending
more time planning the routes. Direct observations also
indicated that the participants were looking for alternative
The t-tests revealed no significant differences between
trial 1 when compared with successive trials for the CP
group, suggesting that there were no obvious improvements
over all subsequent trials. This finding suggests that the CP
method is much more difficult to master and takes longer to
6.3. Participants feedback
Participants were asked about the functionality of the
CHIVE system after performing the trials. In general the
participants from the CP group found that the CP method for
cabling is tiring to operate as the constant holding of the
cable node is necessary when laying the cable sections.
Participants from the PTP group using the PTP technique
felt that the method was easy to use. Participants from
both group felt that the two-dimensional virtual toolbox
was blocking their routing operations thus hampering their
To summarise, the pilot study found that:
It is easier to learn PTP than CP. As the number of trials performed increases the TCT
There is a significant difference between the 10 trials inPTP indicating that the participants have learned the
There is no significance difference detected for CP groupsuggesting that participants are still learning the opera-
tions of the CP method and that more trials are required
before operators become fully proficient.
It has been observed that participants in both groups tendto require more guidance in the operation of the VR
cabling tools and also navigating in the VE during the
Direct observations and feedback from participants alsofound that the CP group was having considerably more
difficulties in routing than the PTP group.
All subjects experienced fatigue whilst conducting thevirtual experiments. Fatigue was experienced more
quickly in the CP group than the PTP group.
The pilot tests fulfilled their purpose of testing systemsoperation and usability.
It was possible to develop feasible cable routes using bothPTP and CP methods.
The pilot tests and the industrial case studies together also
pointed out a number of issues related to both the industrial
trials and future system development, namely:
Future industrial trials will have to be restricted to pre-defined routing paths in order to compare the efficiency of
different designers and alternative cable harness design
solutions, e.g. CAD.
A generic assembly will be used which incorporatesfeatures that can be designed on both the virtual cable
designer and the companies CAD systems.
Longer training times are required to allow users tobecome proficient with the virtual cable design tools.
A new paradigm can now be researched whereby adesigner could design feasible cable routes connections,
using PTP or CP, for electrical connectivity on the virtual
table top (in, say, 212D). In parallel with this, these con-
nections would be automatically mapped using straight
line connections onto the 3D model in the same virtual
space. Rubber banding would be used to tailor the routes
around obstacles. This means that, potentially, cable
harness electrical and mechanical design can be carried
out concurrently instead of sequentially as is the case at
present. Thus the potential for reduction in design lead-
time is substantial.
Comparing subsequent PTP task completion times (TCTs) with trial 1: t-
tests t- and p-values
Trial No. t p
2 2.24 0.09
3 3.54* 0.02
4 3.8* 0.02
5 3.63* 0.02
6 2.46 0.07
7 3.33* 0.03
8 3.20* 0.03
9 3.85* 0.02
10 4.07* 0.02
* Significantly different if p < 0:05.
Comparing subsequent CP task completion times (TCTs) with trial 1: t-
tests t- and p-values
Trial No. t p
2 0.79 0.47
3 0.53 0.62
4 0.87 0.44
5 1.03 0.36
6 1.18 0.30
7 0.87 0.43
8 1.25 0.28
9 1.01 0.37
10 1.39 0.24
42 F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743
This paper has described a novel software tool to assist
users to perform cable routing in a virtual environment. The
system here has been successfully tested in pilot trials. The
recommendations made by the participants during the pilot
study were noted and changes had been incorporated into
virtual cable routing system. Firstly to enable easier user
selection of the cabling tools, the dimension of the virtual
toolbox for choosing cable routing methods has been
enlarged to the size of a billboard within the virtual
environment and the virtual buttons in the toolbox were
also spaced widely to facilitate easier user selection. To
overcome obstruction caused by the virtual toolbox that was
blocking the routing operations, the user is now transported
to another position within the virtual environment with only
the toolbox in view so that they can select the required
cabling tools for subsequent cable layout routing. Once the
required tool or tools are selected, the user can return to their
original position by hitting the return option on the toolbox
in the original location of the user inside the assembly before
the toolbox was invoked and continue the cabling operation
as per normal.
The pilot study also indicated that the CP method is more
difficult to learn since statistical analysis were unable to
detect obvious improvements in performance for all trials.
More repetitions would have to be carried out in order to
bring participants to a level where they are confident in using
the tool for laying cables. Direct observation and feedback
from participants also indicated that it was tiring to use the
CP method when performing the routing experiment. Unlike
the PTP method, the CP cable creation method does not have
the editing facility rubber-banding available to it. To alter
the cable layout, users were required to select the rubber-
banding function by invoking the virtual toolbox. Once the
modification was completed, users were required to invoke
the toolbox again so as to select the CP method and carry on
laying the cable as per normal. Thus from a user-friendly
interface point of view CP has two extra redundant steps
when modifications are required to be performed to the cable
path. The feedback from participants and the results from the
pilot trials have suggested that training on the general usage
of the 3D mouse for navigating and interacting with the VE
might be useful prior to the actual industrial trials. This
exercise may make it easier for the participants to concen-
trate on learning the VR cabling tools since the basic
methods of navigation will have been learnt through the
In the future full scale industrial trials will be carried out
to investigate the viability of this approach to complete the
cable harness routing task as compared to current commer-
cial CAD systems. However, this work did show conclu-
sively that CHDP will be possible in an immersive VR
Combined with the industrial case study investigations, a
new and novel concurrent electrical and mechanical design
paradigm has been recognised. The technology and applica-
tion of immersive VR in this environment provides a new
solution to a traditionally difficult, costly and tail-end part of
the overall product design process.
The authors are grateful to the five companies that
collaborated in this research, for their support of this
work and for access to their expertise and knowledge.
The support of the EPSRC, through access to the equipment
provided under grant GR/K41823, is also very gratefully
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