Designing cable harness assemblies in virtual environments

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<ul><li><p>Designing cable harness assemblies in virtual environments</p><p>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</p><p>Abstract</p><p>Cable harness assemblies are amongst the most costly items in any electro-mechanical product. The domain is not widely recognised as</p><p>an area for academic research. Internationally, some efforts have been made to automate or semi-automate the choice of cable harness path</p><p>through the use of artificial intelligence (AI) via CAD systems, but with little success. Common themes voiced are that the problem is too</p><p>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</p><p>systems to reach an optimum solution. Case study investigations were carried out at five advanced manufacturing organisations to</p><p>determine the current industrial practice. The investigations revealed that the cable harness design and planning (CHDP) process is</p><p>essentially sequential in nature and consists of lengthy activities carried out late in the overall product development cycle. It was also found</p><p>that there has been little attempt to integrate any of the core activities involved. This paper describes work undertaken at Heriot-Watt</p><p>University to research the effectiveness of immersive virtual reality for designing and routing cable harnesses by enhancing the expertise of</p><p>the cable harness designer rather than by replacing the individual via an automated system. The new virtual cable design system developed</p><p>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</p><p>industrial trials in conjunction with a number of high technology equipment manufacturers. These pilot trials, combined with the case</p><p>studies of current practice carried out at the companies, have highlighted a number of issues regarding cable design, particularly that</p><p>immersive VR has a potentially unique role to play in the integration of cable harness electrical and mechanical design activities.</p><p># 2000 Elsevier Science B.V. All rights reserved.</p><p>Keywords: Immersive virtual reality; Cable harness design</p><p>1. Introduction</p><p>Cable harnesses are a vital part of all electro-mechanical</p><p>systems from aircraft and automobiles to personal compu-</p><p>ters and domestic appliances. In many instances the cable</p><p>harness is one of the most costly items in the overall</p><p>engineered system. In spite of this the detail design and</p><p>planning of cable harnesses are often only addressed almost</p><p>as afterthoughts at the end of the product design process.</p><p>Cable harness design and planning (CHDP) in fact cover a</p><p>set of manually intensive, time-consuming and costly activi-</p><p>ties. There is the obvious problem of determining satisfac-</p><p>tory routes for bundles of cables in crowded spaces. The</p><p>wires themselves will vary in size depending on their duties.</p><p>The stiffness and mass distribution of the bundle is deter-</p><p>mined by the size and type of cables involved. Acceptable</p><p>bend radii must be defined as well as the position and</p><p>distribution of the fasteners used to constrain the harness.</p><p>One important concern for harness designers is that of</p><p>voltage drop. Voltage drop is directly proportional to cable</p><p>length and inversely proportional to cable cross-sectional</p><p>area. Ideally, the designer must find a routing configuration</p><p>that maintains a suitable voltage drop for all cables in the</p><p>bundled harness. Fig. 1 shows an example of a completed</p><p>cable harness ready for assembly into a final product.</p><p>Current industrial practice, confirmed in case study inves-</p><p>tigations at five leading UK companies, often requires the</p><p>building of a physical prototype of a new design before</p><p>engineers are able to manually determine the correct cable</p><p>lengths and routes, as well as the numbers and positions of</p><p>fasteners. Once a set of suitable cable paths have been</p><p>chosen and the associated components selected, the results</p><p>are entered into a database that allows the production of two-</p><p>dimensional drawings and parts lists together with assembly</p><p>instructions. It is vital that this information is accurate and</p><p>well-proven since the actual manufacture of the harness</p><p>assembly is often carried out by an external specialist</p><p>supplier.</p><p>The routing problem is further complicated by the vulne-</p><p>rability of the cable harness to decisions made upstream. The</p><p>cable harness may have to be reconfigured after only minor</p><p>changes that affect, say, the chassis and the individual</p><p>modules within a prototype product. The routing process</p><p>Journal of Materials Processing Technology 107 (2000) 3743</p><p>* Corresponding author.</p><p>E-mail address: (J.M. Ritchie).</p><p>0924-0136/00/$ see front matter # 2000 Elsevier Science B.V. All rights reserved.PII: S 0 9 2 4 - 0 1 3 6 ( 0 0 ) 0 0 7 2 5 - 1</p></li><li><p>can even result in the late and expensive re-design of the</p><p>machine chassis to allow the cables to reach their terminal</p><p>points.</p><p>2. Background</p><p>In spite of its industrial importance, cable harness design</p><p>is not widely recognised as an area for academic research.</p><p>Most investigators who have explored the subject have</p><p>attempted to semi-automate or automate the choice of</p><p>harness path through the use of artificial intelligence (AI)</p><p>in conjunction with CAD systems. Such systems are used as</p><p>a review tool for use after the equipment has been designed.</p><p>Park et al. [1] recognised that cable harness design</p><p>requires in depth three-dimensional spatial reasoning. They</p><p>proposed the use of agents to produce different cable</p><p>configurations that satisfy the pin-to-pin connections of a</p><p>typical harness circuit layout and automate routine opera-</p><p>tions such as moving a section of bundles from one position</p><p>to another. Conru and Cutkosky [2,3] report that they have</p><p>incorporated into Park et al.s system a set of algorithms that</p><p>attempt to automate cable routing in a 3D environment. Two</p><p>genetic algorithms were developed to route cable harnesses</p><p>in a 3D environment. Finally, Petrie et al. [4] report the</p><p>development of a harness design system called Next-Link</p><p>that allows different designers to create different harness</p><p>layout concurrently. Next-Link is essentially a manage-</p><p>ment tool that uses a software agent to co-ordinate, update</p><p>and keep track of the work of individual designers, evaluat-</p><p>ing all the routings developed by each designer based on</p><p>satisfying global constraints.</p><p>Much more recently, Cerezuela et al. [5] carried out a case</p><p>study on cable harness design at a helicopter manufacturing</p><p>company. From the case study they found that harness</p><p>design is an iterative process involving schematic, routing</p><p>and component design. It is postulated that harness design is</p><p>a dynamic process and it is not feasible to automate the</p><p>entire activity by computers. Thus, Cerezuela et al. propose</p><p>a conceptual knowledge based decision support system to</p><p>assist in the design of cable harnesses.</p><p>In summary, the review of published academic literature</p><p>in the design and planning of cable harnesses shows that</p><p>much of the limited amount of research in the area has been</p><p>concerned with developing automated or semi-automated</p><p>systems for determining cable routings. The algorithms</p><p>developed tend to be demonstrated in simple geometric</p><p>layouts of components and little evidence is provided that</p><p>the work has been applied in industry.</p><p>3. Industrial case studies</p><p>As part of the present research, case study investigations</p><p>were carried out carried out at five UK advanced electro-</p><p>mechanical technology businesses. These were carried</p><p>through extensive visits, discussions and meetings with</p><p>practitioners and managers. The results were documented</p><p>and returned to the companies involved for their verification.</p><p>Taken together, the five case studies show that the CHDP</p><p>process is essentially sequential in nature and consists of</p><p>lengthy activities carried out late in the overall product</p><p>development cycle. The investigations revealed that there</p><p>has been little attempt to integrate any of the core activities</p><p>involved. It was also found that companies are increasingly</p><p>using CAD based systems to support the design of harnesses.</p><p>There was also no evidence to suggest the use of automated</p><p>or semi-automated harness design tools in use by the</p><p>companies, confirming prior impressions obtained from</p><p>the literature survey.</p><p>The case studies results were used to create a generic</p><p>model shown by Fig. 2 for the CHDP process; this provides</p><p>Fig. 1. Complete cable harness prior to assembly.</p><p>Fig. 2. General stages in the harness design and planning process.</p><p>38 F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743</p></li><li><p>an outline picture of how manufacturing companies in the</p><p>electro-mechanical sector address the cable harness design</p><p>problem. The model is of course subject to detail change in</p><p>particular cases dependent on the types of product manu-</p><p>factured and the required electrical specifications.</p><p>The contention of the work described in this paper is that</p><p>companies prefer to have cable harness design as an inter-</p><p>active technique under the control of the designer. The</p><p>remaining sections of the paper describe a prototype immer-</p><p>sive virtual reality demonstrator system, developed to assist</p><p>designers in producing feasible virtual prototype harness</p><p>assemblies, and the corresponding pilot trial results.</p><p>4. Cable layout using immersive virtual reality</p><p>The virtual design and planning cable routing system at</p><p>Heriot-Watt University is implemented on a Hewlett-Pack-</p><p>ard workstation with additional VR hardware and software</p><p>from Division Ltd. CAD models of a prototype assembly can</p><p>be imported directly into the system which negates the need</p><p>for any extra component modelling. As illustrated in Fig. 3,</p><p>the user interacts with the system by means of a head</p><p>mounted display (HMD). This provides a stereo image of</p><p>the virtual environment. A three-dimensional mouse (3D) is</p><p>used as an input device.</p><p>The ability to touch and feel objects in the real world is</p><p>one that is taken for granted. However, the development of</p><p>viable systems to provide this haptic feedback in virtual</p><p>environments is still the subject of much research [68]. For</p><p>this reason, the system described here makes use of alter-</p><p>native visual and audio cues to highlight collisions. A full</p><p>polygonal collision detection algorithm is available in the</p><p>software. Thus, when a collision occurs, the system utilises</p><p>messages sent from the algorithm to make images of objects</p><p>in the virtual world turn to wire-frame representations. This,</p><p>along with a simple audio cue, informs the user that some-</p><p>thing is amiss (Fig. 4).</p><p>The virtual cable router has five key design tools in its</p><p>operation namely, point-to-point, continuous path,</p><p>way-point routing, rubber banding and size manage-</p><p>ment. Collision detection is inherent within the first three</p><p>features. Point-to-point and continuous path are creation</p><p>functions, whereas way-point routing allows the creation of</p><p>cable bundle assemblies along existing routes. Rubber</p><p>banding is normally used during editing and size manage-</p><p>ment enables the user to amend the size of the model relative</p><p>to the system user. All the features are activated through a</p><p>virtual toolbox as shown in Fig. 5.</p><p>4.1. Point-to-point</p><p>The point-to-point technique of routing cables provides</p><p>the capability to generate outline cable routes rapidly by</p><p>picking positions or nodes in the virtual environment. The</p><p>user simply probes ports located on cable connectors, or a</p><p>point in space, and a section of cable appears between this</p><p>and the last node created as shown in Fig. 6. Once an existing</p><p>node has been picked in an operation it can be moved around</p><p>in three dimensions, stretching or contracting the associated</p><p>cables as required. This editing facility within point-to-point</p><p>is called rubber banding and is described later. The picking</p><p>Fig. 3. A user interacting in the virtual environment.</p><p>Fig. 4. Wire-frame collision warning of a clash with a cable.</p><p>Fig. 5. A virtual toolbox.</p><p>F.M. Ng et al. / Journal of Materials Processing Technology 107 (2000) 3743 39</p></li><li><p>of another node makes that node active and any subsequent</p><p>point chosen in space will create a section of cable</p><p>between it and the active node. By choosing existing nodes,</p><p>multiple spliced or breakaway cable branches can emanate</p><p>from a single node. Some examples of these are shown in</p><p>Fig. 7.</p><p>4.2. Continuous path</p><p>Continuous path generates a cable route by extruding a</p><p>new section from a user-selected node. Thus, by picking an</p><p>existing node, or a port on a connector, a new node is created</p><p>and attached to the virtual hand until the node is released.</p><p>This method has rubber banding implicit within it also; the</p><p>new section changes in length and position as the virtual</p><p>hand moves. In a fashion similar to point-to-point, multiple</p><p>spliced or breakaway cable branches can be produced.</p><p>The user can observe collisions and immediately take</p><p>action to move the section and so as to avoid a clash. Again,</p><p>this method allows for creating nodes with multiple</p><p>branches.</p><p>4.3. Way-point routing</p><p>Having laid one cable, it is possible quickly to lay bundles</p><p>of cables along the same route by using way-points. This is</p><p>achieved by simply choosing the relevant beginning and end</p><p>nodes along the common length of an existing cable between</p><p>which a new cable is to run.</p><p>4.4. Rubber banding</p><p>Once the entire cable layout is produced some modifica-</p><p>tions may be required. The rubber banding facility allows</p><p>the user to re-position either entire sections of cable or</p><p>bundles that are knitted together simply by holding on to and</p><p>subsequently moving a node. Although this editing facility</p><p>stands alone, it has already been mentioned that it is avail-</p><p>able in the point-to-point and, to some extent, the continuous</p><p>path tools.</p><p>4.5. Size management</p><p>The final VR cable layout tool developed and defined as</p><p>part of this research is size management. This provides the</p><p>user with the ability to enlarge or shrink the virtual prototype</p><p>to enable human-scale ergonomic access to either fine</p><p>geometry details or large-scale geometric features within</p><p>the virtual environment as well as deal with any scale of</p><p>product.</p><p>5. System architecture</p><p>The set of nodes and cable sections created by the user are</p><p>stored in a multi-linked graph structure containing a linked</p><p>list of nodes and a further linked list of joins for each node</p><p>[9] (Fig. 8).</p><p>At the end of the routing session, the system generates a</p><p>text file by traversing the graph structure and extracting</p><p>useful information which details the bills-of-materials and</p><p>process planning information associated with the physical</p><p>cable harness. These outputs include the types of end</p><p>connectors and cable configurations selected as well as</p><p>the positions and liaisons that exist between the virtual</p><p>nodes as shown in Fig. 8. The connector type and liai-</p><p>sons/cable configurations indicated in the text file are spe-</p><p>cified by the user during the immersive routing session...</p></li></ul>