Wiring is a major deliverable in just about all electromechanical equipment. From airplanes to semiconductor capital equipment, the key component tying together all of the technological innovations in these machines is the wiring. Until recently wiring system design has merely been an afterthought, the last task accomplished after everything else has been completed. But as the level of complexity of these machines increases, so does the complexity of the wiring. Shrinking market windows and increased competition are causing a re-evaluation of all product development processes, and as a result, old manual methods for wire harness design are being replaced by new automated data-centric systems such as Linius Technologies' EMbassy software.

Figure 1. Fully defining a Wiring System requires reconciliation of a variety of electrical, mechanical, and manufacturing inputs.

A complex wiring system can contain hundreds to thousands of connections, miles of wire, and thousands of related parts such as splices, terminals, seals, plugs, tie wraps, shielding, and overbraid. Coordinating such large amounts of manually entered data is a daunting task. Incorrectly terminated wires, poorly estimated lengths, or misrouted wire bundles can cause weeks of production delays, or worse, a field failure.

Software packages that automate the design of wiring systems need to provide a mechanism to pull together electrical, mechanical, and manufacturing data and display it in a wiring-centric manner. The maturity of today's mechanical and electrical CAD tools has created an opportunity to combine their data and complement their existing automation capabilities with new tools focused on wire harness design.

Figure 2. A Wiring-Centric Database facilitates the accumulation and manipulation of all the necessary data.

A thorough review of the outputs generated to manufacture a wiring system yields a list of the input requirements. Typical harness and cable documentation includes a parts list, a wire-by-wire connectivity list, wire lengths, and wire bundle descriptions. This output data represents a merger of electrical, mechanical, and manufacturing inputs as shown in Figure1.

The most basic electrical input is the wire-by-wire connectivity list. It is typically generated from a schematic or wiring diagram, or can be created in a tabular format. This represents only a fraction of the electrical input, however, as there are many other factors to consider. For example, connectors and associated wire terminating hardware must be chosen, current and voltage requirements must be considered as wire size is selected, and signal compatibility and maximum length constraints are evaluated to ensure proper insulation and shielding are added when needed.

The key mechanical input is the assembly geometry, and this must be merged with the electrical input. Since connectors must be properly located within the housing, connector selection will have an impact on the mechanical space. Sufficient space must be allocated in the assembly for the wire bundles, as the diameter of all the wires and cables must also be accounted for. Wire and bundle lengths are created by considering the point-to-point wire connections in conjunction with the available space for the wire paths.

Finally, manufacturing constraints must be considered in order to minimize cost, maximize quality, and create an easy-to-manufacture harness. Component availability and tooling requirements must be considered. The ease with which the wiring can be manufactured and assembled into the housing also affects the final delivery schedule.

Figure 3. A Virtual Prototype of the wiring system is created and verified in the context of the 3D model.

Without software to correlate all these dependencies and centralize the harness data, the process is extremely tedious and error-prone. As a result, the only way to check consistency is through manual methods, and any design changes must be made in multiple locations. The entire process can be automated by using the EMbassy database, which was created specifically to store wiring-system data coupled with focused applications to enter and manipulate this data.

A wiring design system must provide both accumulation and storage methods for the multidisciplined data as well as access or manipulation of it through applications targeted at specific tasks in the process (see Figure 2). During the accumulation step, the designer loads all relevant inputs into the database, using specially designed interfaces and applications that facilitate gathering the data that is important to the wiring system design. This includes the 3D mechanical structure, the electrical connectivity, initial parts data, and any design constraints that have been identified thus far.

Once the initial inputs have been gathered, the data can be used to design and specify the entire wiring system. Specific applications can be developed for each task: design, evaluation, verification, manufacturing, and documentation. Wiring designers use the applications to create a virtual prototype of the wiring system by drawing the wire bundles in the context of the 3D structure (Figure 3). This virtual prototype eliminates the need to manually measure a hardware prototype. Since all the data is centrally located, options can easily be evaluated. Design constraints such as maximum wire length or bundle diameter can be defined as the design progresses, and then the design can be verified to ensure that all guidelines have been met.

Figure 4. Associative Manufacturing Documentation is created automatically.

After the wiring system has been fully specified, the data can also be manipulated for the downstream functions of manufacturing and documentation (Figure 4). A 2D representation of the harness is used for incoming inspection, field service, and the creation of harness manufacturing fixtures. Because all of the data is stored centrally, these output documents will update automatically when the design changes. All views of the completed system will remain in sync when the design changes. The same is true for reports such as bills of materials, wire lists, and weight and cost estimates.

The centralization of all the data associated with the wiring system keeps all aspects of the design process in sync. The environment is associative, so a design change only needs to made in one location and it will propagate to all appropriate areas. Furthermore, it also enables enhanced automation of the development process and additional automated verification capabilities using data from multiple disciplines.

Centralized data storage also promotes design reuse and enhanced automation. An intelligent reusable library can be built that stores relationships between objects. When a component is added, all of the associated components are automatically assigned. For example, when a connector is chosen, a list of appropriate wire-terminating hardware is provided, and wires can be automatically terminated.

Calculations requiring input from multiple disciplines are also easily enabled. Resistance or impedance calculations can use material-specification and wire-length data to determine if the initial specifications for the electrical signal the wire is carrying have been met. All the data required to calculate total weight and cost is now centrally located, making the calculation a simple byproduct of the design process.

By automating the wire harness process through EMbassy's centralized data storage and specialized applications, the design cycle is shortened, quality is improved, and engineering and product costs are reduced. More specifically, to summarize, the benefits are these:

  • The reliance on a hardware prototype is eliminated by the combination of the mechanical assembly with the electrical connectivity;
  • Detailed electromechanical calculations that require the combination of electrical, mechanical, and manufacturing data are easily performed;
  • Additional time can be spent evaluating options and verifying design rules, rather than gathering and reconciling data;
  • Efficient and consistent process control can be attained, since data is entered and managed on a computer; and
  • Communication among departments is improved, since all groups have access to the same common data repository.

For more information, contact Amy Bunszel, the author of this brief and manager of technical applications at Linius Technologies, 276 Turnpike Road, Westborough, MA 01581; (508) 616-9360; fax (508) 616-9362; e-mail : This email address is being protected from spambots. You need JavaScript enabled to view it.; www.linius.com.

Electronics Tech Briefs Magazine

This article first appeared in the August, 1999 issue of Electronics Tech Briefs Magazine.

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